diff --git a/README.md b/README.md
index 222208d..f852b06 100644
--- a/README.md
+++ b/README.md
@@ -26,7 +26,7 @@ After provisioning Supabase/Upstash/Vercel and `npm run db:push`:
    ```sql
    INSERT INTO bsk.admin_allowlist (email) VALUES ('you@example.com');
    ```
-2. **Seed Vietnamese geo data** (province/ward address dropdowns): `npm run db:seed-geo` (see `scripts/seed-geo.ts`).
+2. **Seed Vietnamese geo data** (province/ward address dropdowns): `npm run db:seed-geo` (see `scripts/seed-geo.mjs`).
 3. **Enable Supabase Realtime** on `bsk.checkups` (Database → Replication) for the live queue.
 4. **Set `CRON_SECRET`** in Vercel so the nightly media-retention sweep (`/api/cron/nightly`, scheduled in `vercel.json`) can authenticate.
 
@@ -34,7 +34,7 @@ See [docs/supabase-shared-config.md](./docs/supabase-shared-config.md) for the s
 
 ## Stack
 
-- **npm** + **Next.js 16** (App Router) + **TypeScript**
+- **npm** + **Next.js 16** (App Router) + **JavaScript with JSDoc types** (checked by tsc)
 - **Supabase** (Postgres + Auth + Storage) — shared across personal projects via schema-per-app
 - **Upstash** Redis + QStash — shared across personal projects via key prefixes
 - **Vercel** for hosting
@@ -48,7 +48,7 @@ See [docs/supabase-shared-config.md](./docs/supabase-shared-config.md) for the s
 
 ## Database
 
-After `npm run db:push`, run `npm run db:gen-types` to refresh `types/supabase-bsk.ts`.
+After `npm run db:push`, run `npm run db:gen-types` to refresh `types/supabase-bsk.d.ts`.
 
 ## License
 
diff --git a/app/[locale]/(app)/admin/doctors/actions.ts b/app/[locale]/(app)/admin/doctors/actions.js
similarity index 84%
rename from app/[locale]/(app)/admin/doctors/actions.ts
rename to app/[locale]/(app)/admin/doctors/actions.js
index f86a571..956e200 100644
--- a/app/[locale]/(app)/admin/doctors/actions.ts
+++ b/app/[locale]/(app)/admin/doctors/actions.js
@@ -15,7 +15,9 @@ import { revalidatePath } from "next/cache";
 
 import { getServerSession } from "@/lib/auth/get-server-session";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
-import { DoctorSchema, type DoctorFormState } from "@/lib/doctors/doctor-schema";
+import { DoctorSchema } from "@/lib/doctors/doctor-schema";
+
+/** @typedef {import('@/lib/doctors/doctor-schema').DoctorFormState} DoctorFormState */
 
 async function revalidateDoctors() {
   const locale = await getLocale();
@@ -23,10 +25,12 @@ async function revalidateDoctors() {
 }
 
 // ── Create (useActionState-compatible) ───────────────────────────────────────
-export async function createDoctorAction(
-  _prev: DoctorFormState,
-  formData: FormData,
-): Promise<DoctorFormState> {
+/**
+ * @param {DoctorFormState} _prev
+ * @param {FormData} formData
+ * @returns {Promise<DoctorFormState>}
+ */
+export async function createDoctorAction(_prev, formData) {
   const t = await getTranslations("admin.doctors");
 
   const session = await getServerSession();
@@ -41,7 +45,7 @@ export async function createDoctorAction(
   if (!parsed.success) {
     return {
       status: "error",
-      fieldErrors: parsed.error.flatten().fieldErrors as Record<string, string[]>,
+      fieldErrors: /** @type {Record<string, string[]>} */ (parsed.error.flatten().fieldErrors),
       formError: null,
     };
   }
@@ -70,7 +74,11 @@ export async function createDoctorAction(
 }
 
 // ── Update ───────────────────────────────────────────────────────────────────
-export async function updateDoctorAction(formData: FormData): Promise<void> {
+/**
+ * @param {FormData} formData
+ * @returns {Promise<void>}
+ */
+export async function updateDoctorAction(formData) {
   const session = await getServerSession();
   if (session?.role !== "admin") return;
 
@@ -98,7 +106,11 @@ export async function updateDoctorAction(formData: FormData): Promise<void> {
 }
 
 // ── Soft-delete (deactivate) ─────────────────────────────────────────────────
-export async function deactivateDoctorAction(formData: FormData): Promise<void> {
+/**
+ * @param {FormData} formData
+ * @returns {Promise<void>}
+ */
+export async function deactivateDoctorAction(formData) {
   const session = await getServerSession();
   if (session?.role !== "admin") return;
 
diff --git a/app/[locale]/(app)/admin/doctors/add-doctor-form.tsx b/app/[locale]/(app)/admin/doctors/add-doctor-form.jsx
similarity index 87%
rename from app/[locale]/(app)/admin/doctors/add-doctor-form.tsx
rename to app/[locale]/(app)/admin/doctors/add-doctor-form.jsx
index d551a53..e39aceb 100644
--- a/app/[locale]/(app)/admin/doctors/add-doctor-form.tsx
+++ b/app/[locale]/(app)/admin/doctors/add-doctor-form.jsx
@@ -14,18 +14,21 @@ import { useTranslations } from "next-intl";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
-import { DoctorSchema, type DoctorInput, type DoctorFormState } from "@/lib/doctors/doctor-schema";
+import { DoctorSchema } from "@/lib/doctors/doctor-schema";
 import { createDoctorAction } from "./actions";
 
+/** @typedef {import('@/lib/doctors/doctor-schema').DoctorInput} DoctorInput */
+/** @typedef {import('@/lib/doctors/doctor-schema').DoctorFormState} DoctorFormState */
+
+/** Admin form to add a doctor row. @returns {import("react").JSX.Element} */
 export function AddDoctorForm() {
   const t = useTranslations("admin.doctors");
 
-  const [state, dispatchAction, isPending] = useActionState<DoctorFormState, FormData>(
-    createDoctorAction,
-    { status: "idle" },
-  );
+  const [state, dispatchAction, isPending] = useActionState(createDoctorAction, {
+    status: "idle",
+  });
 
-  const form = useForm<DoctorInput>({
+  const form = useForm({
     resolver: zodResolver(DoctorSchema),
     mode: "onBlur",
     defaultValues: { firstName: "", lastName: "" },
diff --git a/app/[locale]/(app)/admin/doctors/page.tsx b/app/[locale]/(app)/admin/doctors/page.jsx
similarity index 94%
rename from app/[locale]/(app)/admin/doctors/page.tsx
rename to app/[locale]/(app)/admin/doctors/page.jsx
index 7499438..317308e 100644
--- a/app/[locale]/(app)/admin/doctors/page.tsx
+++ b/app/[locale]/(app)/admin/doctors/page.jsx
@@ -14,7 +14,11 @@ import { Input } from "@/components/ui/input";
 import { AddDoctorForm } from "./add-doctor-form";
 import { updateDoctorAction, deactivateDoctorAction } from "./actions";
 
-export default async function DoctorsPage({ params }: { params: Promise<{ locale: string }> }) {
+/**
+ * @param {{ params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function DoctorsPage({ params }) {
   await params; // Next.js 16: params is async.
   const t = await getTranslations("admin.doctors");
 
diff --git a/app/[locale]/(app)/admin/invite/actions.ts b/app/[locale]/(app)/admin/invite/actions.js
similarity index 90%
rename from app/[locale]/(app)/admin/invite/actions.ts
rename to app/[locale]/(app)/admin/invite/actions.js
index c1f2ed8..e23c3e9 100644
--- a/app/[locale]/(app)/admin/invite/actions.ts
+++ b/app/[locale]/(app)/admin/invite/actions.js
@@ -24,15 +24,19 @@ import { getTranslations } from "next-intl/server";
 import { getServerSession } from "@/lib/auth/get-server-session";
 import { createSupabaseAdminClient } from "@/lib/supabase/admin";
 import { createRateLimiter } from "@/lib/upstash";
-import { InviteUserSchema, type InviteUserState } from "@/lib/auth/invite-schema";
+import { InviteUserSchema } from "@/lib/auth/invite-schema";
+
+/** @typedef {import('@/lib/auth/invite-schema').InviteUserState} InviteUserState */
 
 // Bound SMTP spend on the SHARED project: cap invites per admin. 20 / hour.
 const inviteLimiter = createRateLimiter("invite", 20, 3600);
 
-export async function inviteUserAction(
-  _prevState: InviteUserState,
-  formData: FormData,
-): Promise<InviteUserState> {
+/**
+ * @param {InviteUserState} _prevState
+ * @param {FormData} formData
+ * @returns {Promise<InviteUserState>}
+ */
+export async function inviteUserAction(_prevState, formData) {
   const t = await getTranslations("admin.invite");
 
   // ── Caller-role check (defense-in-depth) ──────────────────────────────────
@@ -59,7 +63,7 @@ export async function inviteUserAction(
     const flat = parsed.error.flatten();
     return {
       status: "error",
-      fieldErrors: flat.fieldErrors as Record<string, string[]>,
+      fieldErrors: /** @type {Record<string, string[]>} */ (flat.fieldErrors),
       formError: null,
     };
   }
@@ -75,7 +79,7 @@ export async function inviteUserAction(
     // An existing email (often a sibling-app user on the shared auth pool)
     // makes inviteUserByEmail fail — report it as "already enrolled/known"
     // rather than a generic error so the admin understands what happened.
-    const code = (inviteError as { code?: string } | null)?.code;
+    const code = /** @type {{ code?: string } | null} */ (inviteError)?.code;
     const msg = inviteError?.message?.toLowerCase() ?? "";
     const emailExists =
       code === "email_exists" ||
diff --git a/app/[locale]/(app)/admin/invite/invite-user-form.tsx b/app/[locale]/(app)/admin/invite/invite-user-form.jsx
similarity index 89%
rename from app/[locale]/(app)/admin/invite/invite-user-form.tsx
rename to app/[locale]/(app)/admin/invite/invite-user-form.jsx
index 820052f..59d0c5d 100644
--- a/app/[locale]/(app)/admin/invite/invite-user-form.tsx
+++ b/app/[locale]/(app)/admin/invite/invite-user-form.jsx
@@ -23,30 +23,29 @@ import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
 import { appRoles } from "@/lib/db/roles";
-import {
-  InviteUserSchema,
-  type InviteUserInput,
-  type InviteUserState,
-} from "@/lib/auth/invite-schema";
+import { InviteUserSchema } from "@/lib/auth/invite-schema";
 import { inviteUserAction } from "./actions";
 
+/** @typedef {import('@/lib/auth/invite-schema').InviteUserInput} InviteUserInput */
+/** @typedef {import('@/lib/auth/invite-schema').InviteUserState} InviteUserState */
+
 // ---------------------------------------------------------------------------
 // Component
 // ---------------------------------------------------------------------------
 
+/** Admin form that invites a user by email with a role. @returns {import("react").JSX.Element} */
 export function InviteUserForm() {
   const t = useTranslations("admin.invite");
   const tRoles = useTranslations("roles");
 
-  const [state, dispatchAction, isPending] = useActionState<InviteUserState, FormData>(
-    inviteUserAction,
-    { status: "idle" },
-  );
+  const [state, dispatchAction, isPending] = useActionState(inviteUserAction, {
+    status: "idle",
+  });
 
-  const form = useForm<InviteUserInput>({
+  const form = useForm({
     resolver: zodResolver(InviteUserSchema),
     mode: "onBlur",
-    defaultValues: { email: "", role: "patient" },
+    defaultValues: { email: "", role: /** @type {InviteUserInput["role"]} */ ("patient") },
   });
 
   const { errors: fieldErrors } = form.formState;
diff --git a/app/[locale]/(app)/admin/invite/page.tsx b/app/[locale]/(app)/admin/invite/page.jsx
similarity index 93%
rename from app/[locale]/(app)/admin/invite/page.tsx
rename to app/[locale]/(app)/admin/invite/page.jsx
index 9563921..2cc0040 100644
--- a/app/[locale]/(app)/admin/invite/page.tsx
+++ b/app/[locale]/(app)/admin/invite/page.jsx
@@ -12,6 +12,7 @@
 import { getTranslations } from "next-intl/server";
 import { InviteUserForm } from "./invite-user-form";
 
+/** @returns {Promise<import("react").JSX.Element>} */
 export default async function AdminInvitePage() {
   const t = await getTranslations("admin.invite");
 
diff --git a/app/[locale]/(app)/admin/layout.tsx b/app/[locale]/(app)/admin/layout.jsx
similarity index 75%
rename from app/[locale]/(app)/admin/layout.tsx
rename to app/[locale]/(app)/admin/layout.jsx
index e326549..7d36713 100644
--- a/app/[locale]/(app)/admin/layout.tsx
+++ b/app/[locale]/(app)/admin/layout.jsx
@@ -11,16 +11,13 @@
  * receiving a 404, which would confirm that restricted admin routes exist.
  */
 
-import type { ReactNode } from "react";
 import { requireRole } from "@/lib/auth/require-role";
 
-export default async function AdminLayout({
-  children,
-  params,
-}: {
-  children: ReactNode;
-  params: Promise<{ locale: string }>;
-}) {
+/**
+ * @param {{ children: import("react").ReactNode, params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function AdminLayout({ children, params }) {
   const { locale } = await params;
 
   // Redirects to /dashboard if role !== 'admin'.
diff --git a/app/[locale]/(app)/admin/medicines/[id]/edit/page.tsx b/app/[locale]/(app)/admin/medicines/[id]/edit/page.jsx
similarity index 87%
rename from app/[locale]/(app)/admin/medicines/[id]/edit/page.tsx
rename to app/[locale]/(app)/admin/medicines/[id]/edit/page.jsx
index 894c2f6..e3372d0 100644
--- a/app/[locale]/(app)/admin/medicines/[id]/edit/page.tsx
+++ b/app/[locale]/(app)/admin/medicines/[id]/edit/page.jsx
@@ -4,11 +4,11 @@ import { createSupabaseServerClient } from "@/lib/supabase/server";
 import { MedicineForm } from "../../medicine-form";
 import { updateMedicineAction } from "../../actions";
 
-export default async function EditMedicinePage({
-  params,
-}: {
-  params: Promise<{ locale: string; id: string }>;
-}) {
+/**
+ * @param {{ params: Promise<{ locale: string, id: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function EditMedicinePage({ params }) {
   const { id } = await params;
   const t = await getTranslations("admin.medicines");
   const medId = Number(id);
diff --git a/app/[locale]/(app)/admin/medicines/actions.ts b/app/[locale]/(app)/admin/medicines/actions.js
similarity index 74%
rename from app/[locale]/(app)/admin/medicines/actions.ts
rename to app/[locale]/(app)/admin/medicines/actions.js
index 3a5fa77..2063405 100644
--- a/app/[locale]/(app)/admin/medicines/actions.ts
+++ b/app/[locale]/(app)/admin/medicines/actions.js
@@ -8,14 +8,15 @@ import { revalidatePath } from "next/cache";
 import { redirect } from "@/i18n/navigation";
 import { getServerSession } from "@/lib/auth/get-server-session";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
-import {
-  MedicineSchema,
-  type MedicineFormState,
-  type MedicineInput,
-} from "@/lib/catalog/medicine-schema";
+import { MedicineSchema } from "@/lib/catalog/medicine-schema";
 
-function readForm(formData: FormData) {
-  const get = (k: string) => String(formData.get(k) ?? "");
+/** @typedef {import('@/lib/catalog/medicine-schema').MedicineFormState} MedicineFormState */
+/** @typedef {import('@/lib/catalog/medicine-schema').MedicineInput} MedicineInput */
+
+/** @param {FormData} formData */
+function readForm(formData) {
+  /** @param {string} k */
+  const get = (k) => String(formData.get(k) ?? "");
   return {
     name: get("name"),
     unit: get("unit"),
@@ -26,7 +27,8 @@ function readForm(formData: FormData) {
   };
 }
 
-function toRow(d: MedicineInput) {
+/** @param {MedicineInput} d */
+function toRow(d) {
   const cost = d.costPrice.trim() ? Number(d.costPrice) : null;
   return {
     name: d.name,
@@ -38,16 +40,19 @@ function toRow(d: MedicineInput) {
   };
 }
 
-async function finish(): Promise<never> {
+/** @returns {Promise<never>} */
+async function finish() {
   const locale = await getLocale();
   revalidatePath(`/${locale}/admin/medicines`);
   return redirect({ href: `/${locale}/admin/medicines`, locale });
 }
 
-export async function createMedicineAction(
-  _prev: MedicineFormState,
-  formData: FormData,
-): Promise<MedicineFormState> {
+/**
+ * @param {MedicineFormState} _prev
+ * @param {FormData} formData
+ * @returns {Promise<MedicineFormState>}
+ */
+export async function createMedicineAction(_prev, formData) {
   const t = await getTranslations("admin.medicines");
   const session = await getServerSession();
   if (session?.role !== "admin")
@@ -57,7 +62,7 @@ export async function createMedicineAction(
   if (!parsed.success) {
     return {
       status: "error",
-      fieldErrors: parsed.error.flatten().fieldErrors as Record<string, string[]>,
+      fieldErrors: /** @type {Record<string, string[]>} */ (parsed.error.flatten().fieldErrors),
       formError: null,
     };
   }
@@ -78,10 +83,12 @@ export async function createMedicineAction(
   return finish();
 }
 
-export async function updateMedicineAction(
-  _prev: MedicineFormState,
-  formData: FormData,
-): Promise<MedicineFormState> {
+/**
+ * @param {MedicineFormState} _prev
+ * @param {FormData} formData
+ * @returns {Promise<MedicineFormState>}
+ */
+export async function updateMedicineAction(_prev, formData) {
   const t = await getTranslations("admin.medicines");
   const session = await getServerSession();
   if (session?.role !== "admin")
@@ -94,7 +101,7 @@ export async function updateMedicineAction(
       status: "error",
       fieldErrors: parsed.success
         ? {}
-        : (parsed.error.flatten().fieldErrors as Record<string, string[]>),
+        : /** @type {Record<string, string[]>} */ (parsed.error.flatten().fieldErrors),
       formError: parsed.success ? t("errorGeneric") : null,
     };
   }
@@ -111,7 +118,11 @@ export async function updateMedicineAction(
   return finish();
 }
 
-export async function deactivateMedicineAction(formData: FormData): Promise<void> {
+/**
+ * @param {FormData} formData
+ * @returns {Promise<void>}
+ */
+export async function deactivateMedicineAction(formData) {
   const session = await getServerSession();
   if (session?.role !== "admin") return;
 
diff --git a/app/[locale]/(app)/admin/medicines/medicine-form.tsx b/app/[locale]/(app)/admin/medicines/medicine-form.jsx
similarity index 68%
rename from app/[locale]/(app)/admin/medicines/medicine-form.tsx
rename to app/[locale]/(app)/admin/medicines/medicine-form.jsx
index 87fc0fe..0ff25f7 100644
--- a/app/[locale]/(app)/admin/medicines/medicine-form.tsx
+++ b/app/[locale]/(app)/admin/medicines/medicine-form.jsx
@@ -8,35 +8,41 @@ import { useTranslations } from "next-intl";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
-import type { MedicineFormState } from "@/lib/catalog/medicine-schema";
 
-export type MedicineDefaults = {
-  id?: number;
-  name: string;
-  unit: string;
-  salePrice: string;
-  costPrice: string;
-  company: string;
-  route: string;
-};
+/** @typedef {import('@/lib/catalog/medicine-schema').MedicineFormState} MedicineFormState */
 
-export function MedicineForm({
-  mode,
-  action,
-  defaults,
-}: {
-  mode: "create" | "edit";
-  action: (prev: MedicineFormState, formData: FormData) => Promise<MedicineFormState>;
-  defaults: MedicineDefaults;
-}) {
+/**
+ * @typedef {Object} MedicineDefaults
+ * @property {number} [id]
+ * @property {string} name
+ * @property {string} unit
+ * @property {string} salePrice
+ * @property {string} costPrice
+ * @property {string} company
+ * @property {string} route
+ */
+
+/**
+ * @param {{
+ *   mode: "create" | "edit",
+ *   action: (prev: MedicineFormState, formData: FormData) => Promise<MedicineFormState>,
+ *   defaults: MedicineDefaults,
+ * }} props
+ */
+export function MedicineForm({ mode, action, defaults }) {
   const t = useTranslations("admin.medicines");
-  const [state, dispatch, isPending] = useActionState<MedicineFormState, FormData>(action, {
+  const [state, dispatch, isPending] = useActionState(action, {
     status: "idle",
   });
   const fe = state.status === "error" ? state.fieldErrors : {};
   const formError = state.status === "error" ? state.formError : null;
 
-  const field = (name: keyof MedicineDefaults, label: string, type = "text") => (
+  /**
+   * @param {keyof MedicineDefaults} name
+   * @param {string} label
+   * @param {string} [type]
+   */
+  const field = (name, label, type = "text") => (
     <div className="space-y-1.5">
       <Label htmlFor={name}>{label}</Label>
       <Input
diff --git a/app/[locale]/(app)/admin/medicines/new/page.tsx b/app/[locale]/(app)/admin/medicines/new/page.jsx
similarity index 76%
rename from app/[locale]/(app)/admin/medicines/new/page.tsx
rename to app/[locale]/(app)/admin/medicines/new/page.jsx
index f7d9f71..61f7a98 100644
--- a/app/[locale]/(app)/admin/medicines/new/page.tsx
+++ b/app/[locale]/(app)/admin/medicines/new/page.jsx
@@ -2,7 +2,11 @@ import { getTranslations } from "next-intl/server";
 import { MedicineForm } from "../medicine-form";
 import { createMedicineAction } from "../actions";
 
-export default async function NewMedicinePage({ params }: { params: Promise<{ locale: string }> }) {
+/**
+ * @param {{ params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function NewMedicinePage({ params }) {
   await params;
   const t = await getTranslations("admin.medicines");
   return (
diff --git a/app/[locale]/(app)/admin/medicines/page.tsx b/app/[locale]/(app)/admin/medicines/page.jsx
similarity index 80%
rename from app/[locale]/(app)/admin/medicines/page.tsx
rename to app/[locale]/(app)/admin/medicines/page.jsx
index 7ad849e..f51bb45 100644
--- a/app/[locale]/(app)/admin/medicines/page.tsx
+++ b/app/[locale]/(app)/admin/medicines/page.jsx
@@ -6,9 +6,14 @@ import { createSupabaseServerClient } from "@/lib/supabase/server";
 import { Button } from "@/components/ui/button";
 import { deactivateMedicineAction } from "./actions";
 
-const vnd = (n: number) => `${new Intl.NumberFormat("vi-VN").format(n)} ₫`;
+/** @param {number} n */
+const vnd = (n) => `${new Intl.NumberFormat("vi-VN").format(n)} ₫`;
 
-export default async function MedicinesPage({ params }: { params: Promise<{ locale: string }> }) {
+/**
+ * @param {{ params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function MedicinesPage({ params }) {
   const { locale } = await params;
   const t = await getTranslations("admin.medicines");
 
@@ -25,7 +30,7 @@ export default async function MedicinesPage({ params }: { params: Promise<{ loca
       <div className="mb-6 flex items-center justify-between gap-4">
         <h1 className="text-foreground text-xl font-semibold">{t("title")}</h1>
         <Button asChild size="lg">
-          <Link href="/admin/medicines/new" locale={locale as "vi" | "en"}>
+          <Link href="/admin/medicines/new" locale={/** @type {"vi" | "en"} */ (locale)}>
             {t("new")}
           </Link>
         </Button>
@@ -45,7 +50,10 @@ export default async function MedicinesPage({ params }: { params: Promise<{ loca
               </div>
               <div className="flex shrink-0 items-center gap-1">
                 <Button asChild variant="outline">
-                  <Link href={`/admin/medicines/${m.id}/edit`} locale={locale as "vi" | "en"}>
+                  <Link
+                    href={`/admin/medicines/${m.id}/edit`}
+                    locale={/** @type {"vi" | "en"} */ (locale)}
+                  >
                     {t("edit")}
                   </Link>
                 </Button>
diff --git a/app/[locale]/(app)/admin/reports/page.tsx b/app/[locale]/(app)/admin/reports/page.jsx
similarity index 94%
rename from app/[locale]/(app)/admin/reports/page.tsx
rename to app/[locale]/(app)/admin/reports/page.jsx
index 2456196..9c24d7b 100644
--- a/app/[locale]/(app)/admin/reports/page.tsx
+++ b/app/[locale]/(app)/admin/reports/page.jsx
@@ -8,7 +8,11 @@ import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
 import { routing } from "@/i18n/routing";
 
-export default async function ReportsPage({ params }: { params: Promise<{ locale: string }> }) {
+/**
+ * @param {{ params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function ReportsPage({ params }) {
   const { locale } = await params;
   const t = await getTranslations("reports");
 
diff --git a/app/[locale]/(app)/admin/services/actions.ts b/app/[locale]/(app)/admin/services/actions.js
similarity index 79%
rename from app/[locale]/(app)/admin/services/actions.ts
rename to app/[locale]/(app)/admin/services/actions.js
index d5e26b4..a74e17a 100644
--- a/app/[locale]/(app)/admin/services/actions.ts
+++ b/app/[locale]/(app)/admin/services/actions.js
@@ -7,17 +7,21 @@ import { revalidatePath } from "next/cache";
 
 import { getServerSession } from "@/lib/auth/get-server-session";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
-import { ServiceSchema, type ServiceFormState } from "@/lib/catalog/service-schema";
+import { ServiceSchema } from "@/lib/catalog/service-schema";
+
+/** @typedef {import('@/lib/catalog/service-schema').ServiceFormState} ServiceFormState */
 
 async function revalidateServices() {
   const locale = await getLocale();
   revalidatePath(`/${locale}/admin/services`);
 }
 
-export async function createServiceAction(
-  _prev: ServiceFormState,
-  formData: FormData,
-): Promise<ServiceFormState> {
+/**
+ * @param {ServiceFormState} _prev
+ * @param {FormData} formData
+ * @returns {Promise<ServiceFormState>}
+ */
+export async function createServiceAction(_prev, formData) {
   const t = await getTranslations("admin.services");
   const session = await getServerSession();
   if (session?.role !== "admin")
@@ -30,7 +34,7 @@ export async function createServiceAction(
   if (!parsed.success) {
     return {
       status: "error",
-      fieldErrors: parsed.error.flatten().fieldErrors as Record<string, string[]>,
+      fieldErrors: /** @type {Record<string, string[]>} */ (parsed.error.flatten().fieldErrors),
       formError: null,
     };
   }
@@ -52,7 +56,11 @@ export async function createServiceAction(
   return { status: "success", serviceName: parsed.data.name };
 }
 
-export async function updateServiceAction(formData: FormData): Promise<void> {
+/**
+ * @param {FormData} formData
+ * @returns {Promise<void>}
+ */
+export async function updateServiceAction(formData) {
   const session = await getServerSession();
   if (session?.role !== "admin") return;
 
@@ -78,7 +86,11 @@ export async function updateServiceAction(formData: FormData): Promise<void> {
   }
 }
 
-export async function deactivateServiceAction(formData: FormData): Promise<void> {
+/**
+ * @param {FormData} formData
+ * @returns {Promise<void>}
+ */
+export async function deactivateServiceAction(formData) {
   const session = await getServerSession();
   if (session?.role !== "admin") return;
 
diff --git a/app/[locale]/(app)/admin/services/add-service-form.tsx b/app/[locale]/(app)/admin/services/add-service-form.jsx
similarity index 85%
rename from app/[locale]/(app)/admin/services/add-service-form.tsx
rename to app/[locale]/(app)/admin/services/add-service-form.jsx
index 417e4a4..dfd467d 100644
--- a/app/[locale]/(app)/admin/services/add-service-form.tsx
+++ b/app/[locale]/(app)/admin/services/add-service-form.jsx
@@ -12,18 +12,17 @@ import { useTranslations } from "next-intl";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
-import type { ServiceFormState } from "@/lib/catalog/service-schema";
 import { createServiceAction } from "./actions";
 
+/** @typedef {import('@/lib/catalog/service-schema').ServiceFormState} ServiceFormState */
+
+/** Admin form to add a service row. @returns {import("react").JSX.Element} */
 export function AddServiceForm() {
   const t = useTranslations("admin.services");
-  const formRef = useRef<HTMLFormElement>(null);
-  const [state, dispatch, isPending] = useActionState<ServiceFormState, FormData>(
-    createServiceAction,
-    {
-      status: "idle",
-    },
-  );
+  const formRef = useRef(/** @type {HTMLFormElement | null} */ (null));
+  const [state, dispatch, isPending] = useActionState(createServiceAction, {
+    status: "idle",
+  });
 
   useEffect(() => {
     if (state.status === "success") formRef.current?.reset();
diff --git a/app/[locale]/(app)/admin/services/page.tsx b/app/[locale]/(app)/admin/services/page.jsx
similarity index 94%
rename from app/[locale]/(app)/admin/services/page.tsx
rename to app/[locale]/(app)/admin/services/page.jsx
index 0cf9e4e..5ca5799 100644
--- a/app/[locale]/(app)/admin/services/page.tsx
+++ b/app/[locale]/(app)/admin/services/page.jsx
@@ -7,7 +7,11 @@ import { Input } from "@/components/ui/input";
 import { AddServiceForm } from "./add-service-form";
 import { updateServiceAction, deactivateServiceAction } from "./actions";
 
-export default async function ServicesPage({ params }: { params: Promise<{ locale: string }> }) {
+/**
+ * @param {{ params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function ServicesPage({ params }) {
   await params;
   const t = await getTranslations("admin.services");
 
diff --git a/app/[locale]/(app)/admin/settings/actions.ts b/app/[locale]/(app)/admin/settings/actions.js
similarity index 76%
rename from app/[locale]/(app)/admin/settings/actions.ts
rename to app/[locale]/(app)/admin/settings/actions.js
index 6698aa5..02267e8 100644
--- a/app/[locale]/(app)/admin/settings/actions.ts
+++ b/app/[locale]/(app)/admin/settings/actions.js
@@ -11,17 +11,19 @@ import { revalidatePath } from "next/cache";
 
 import { getServerSession } from "@/lib/auth/get-server-session";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
-import {
-  ClinicSettingsSchema,
-  type ClinicSettingsState,
-} from "@/lib/clinic/clinic-settings-schema";
+import { ClinicSettingsSchema } from "@/lib/clinic/clinic-settings-schema";
 
-const emptyToNull = (s: string) => (s.length > 0 ? s : null);
+/** @typedef {import('@/lib/clinic/clinic-settings-schema').ClinicSettingsState} ClinicSettingsState */
 
-export async function updateClinicSettingsAction(
-  _prev: ClinicSettingsState,
-  formData: FormData,
-): Promise<ClinicSettingsState> {
+/** @param {string} s */
+const emptyToNull = (s) => (s.length > 0 ? s : null);
+
+/**
+ * @param {ClinicSettingsState} _prev
+ * @param {FormData} formData
+ * @returns {Promise<ClinicSettingsState>}
+ */
+export async function updateClinicSettingsAction(_prev, formData) {
   const t = await getTranslations("admin.settings");
 
   const session = await getServerSession();
@@ -38,7 +40,7 @@ export async function updateClinicSettingsAction(
   if (!parsed.success) {
     return {
       status: "error",
-      fieldErrors: parsed.error.flatten().fieldErrors as Record<string, string[]>,
+      fieldErrors: /** @type {Record<string, string[]>} */ (parsed.error.flatten().fieldErrors),
       formError: null,
     };
   }
diff --git a/app/[locale]/(app)/admin/settings/clinic-settings-form.tsx b/app/[locale]/(app)/admin/settings/clinic-settings-form.jsx
similarity index 77%
rename from app/[locale]/(app)/admin/settings/clinic-settings-form.tsx
rename to app/[locale]/(app)/admin/settings/clinic-settings-form.jsx
index 117443d..16d6274 100644
--- a/app/[locale]/(app)/admin/settings/clinic-settings-form.tsx
+++ b/app/[locale]/(app)/admin/settings/clinic-settings-form.jsx
@@ -13,24 +13,23 @@ import { useTranslations } from "next-intl";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
-import {
-  ClinicSettingsSchema,
-  type ClinicSettingsInput,
-  type ClinicSettingsState,
-} from "@/lib/clinic/clinic-settings-schema";
+import { ClinicSettingsSchema } from "@/lib/clinic/clinic-settings-schema";
 import { updateClinicSettingsAction } from "./actions";
 
-const FIELDS = ["name", "address", "phone", "prefix"] as const;
+/** @typedef {import('@/lib/clinic/clinic-settings-schema').ClinicSettingsInput} ClinicSettingsInput */
+/** @typedef {import('@/lib/clinic/clinic-settings-schema').ClinicSettingsState} ClinicSettingsState */
 
-export function ClinicSettingsForm({ defaults }: { defaults: ClinicSettingsInput }) {
+const FIELDS = /** @type {const} */ (["name", "address", "phone", "prefix"]);
+
+/** @param {{ defaults: ClinicSettingsInput }} props */
+export function ClinicSettingsForm({ defaults }) {
   const t = useTranslations("admin.settings");
 
-  const [state, dispatchAction, isPending] = useActionState<ClinicSettingsState, FormData>(
-    updateClinicSettingsAction,
-    { status: "idle" },
-  );
+  const [state, dispatchAction, isPending] = useActionState(updateClinicSettingsAction, {
+    status: "idle",
+  });
 
-  const form = useForm<ClinicSettingsInput>({
+  const form = useForm({
     resolver: zodResolver(ClinicSettingsSchema),
     mode: "onBlur",
     defaultValues: defaults,
diff --git a/app/[locale]/(app)/admin/settings/page.tsx b/app/[locale]/(app)/admin/settings/page.jsx
similarity index 85%
rename from app/[locale]/(app)/admin/settings/page.tsx
rename to app/[locale]/(app)/admin/settings/page.jsx
index 08fb609..0efbc64 100644
--- a/app/[locale]/(app)/admin/settings/page.tsx
+++ b/app/[locale]/(app)/admin/settings/page.jsx
@@ -9,11 +9,11 @@ import { getTranslations } from "next-intl/server";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
 import { ClinicSettingsForm } from "./clinic-settings-form";
 
-export default async function ClinicSettingsPage({
-  params,
-}: {
-  params: Promise<{ locale: string }>;
-}) {
+/**
+ * @param {{ params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function ClinicSettingsPage({ params }) {
   await params; // Next.js 16: params is async.
   const t = await getTranslations("admin.settings");
 
diff --git a/app/[locale]/(app)/admin/staff/actions.ts b/app/[locale]/(app)/admin/staff/actions.js
similarity index 89%
rename from app/[locale]/(app)/admin/staff/actions.ts
rename to app/[locale]/(app)/admin/staff/actions.js
index 92474bf..8cedb37 100644
--- a/app/[locale]/(app)/admin/staff/actions.ts
+++ b/app/[locale]/(app)/admin/staff/actions.js
@@ -22,7 +22,11 @@ async function revalidateStaff() {
   revalidatePath(`/${locale}/admin/staff`);
 }
 
-export async function updateStaffRoleAction(formData: FormData): Promise<void> {
+/**
+ * @param {FormData} formData
+ * @returns {Promise<void>}
+ */
+export async function updateStaffRoleAction(formData) {
   const session = await getServerSession();
   if (session?.role !== "admin") return;
 
@@ -43,7 +47,11 @@ export async function updateStaffRoleAction(formData: FormData): Promise<void> {
   }
 }
 
-export async function removeStaffAction(formData: FormData): Promise<void> {
+/**
+ * @param {FormData} formData
+ * @returns {Promise<void>}
+ */
+export async function removeStaffAction(formData) {
   const session = await getServerSession();
   if (session?.role !== "admin") return;
 
diff --git a/app/[locale]/(app)/admin/staff/page.tsx b/app/[locale]/(app)/admin/staff/page.jsx
similarity index 95%
rename from app/[locale]/(app)/admin/staff/page.tsx
rename to app/[locale]/(app)/admin/staff/page.jsx
index 5baec94..6599eab 100644
--- a/app/[locale]/(app)/admin/staff/page.tsx
+++ b/app/[locale]/(app)/admin/staff/page.jsx
@@ -13,7 +13,11 @@ import { appRoles } from "@/lib/db/roles";
 import { Button } from "@/components/ui/button";
 import { updateStaffRoleAction, removeStaffAction } from "./actions";
 
-export default async function StaffPage({ params }: { params: Promise<{ locale: string }> }) {
+/**
+ * @param {{ params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function StaffPage({ params }) {
   await params;
   const t = await getTranslations("admin.staff");
   const tRoles = await getTranslations("roles");
diff --git a/app/[locale]/(app)/admin/templates/[id]/edit/page.tsx b/app/[locale]/(app)/admin/templates/[id]/edit/page.jsx
similarity index 87%
rename from app/[locale]/(app)/admin/templates/[id]/edit/page.tsx
rename to app/[locale]/(app)/admin/templates/[id]/edit/page.jsx
index a2a526b..db923f6 100644
--- a/app/[locale]/(app)/admin/templates/[id]/edit/page.tsx
+++ b/app/[locale]/(app)/admin/templates/[id]/edit/page.jsx
@@ -7,11 +7,11 @@ import { fieldsJsonToText } from "@/lib/templates/template-schema";
 import { TemplateForm } from "../../template-form";
 import { updateTemplateAction } from "../../actions";
 
-export default async function EditTemplatePage({
-  params,
-}: {
-  params: Promise<{ locale: string; id: string }>;
-}) {
+/**
+ * @param {{ params: Promise<{ locale: string, id: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function EditTemplatePage({ params }) {
   const { id } = await params;
   const t = await getTranslations("admin.templates");
   const templateId = Number(id);
diff --git a/app/[locale]/(app)/admin/templates/actions.ts b/app/[locale]/(app)/admin/templates/actions.js
similarity index 74%
rename from app/[locale]/(app)/admin/templates/actions.ts
rename to app/[locale]/(app)/admin/templates/actions.js
index 70fac41..da514ee 100644
--- a/app/[locale]/(app)/admin/templates/actions.ts
+++ b/app/[locale]/(app)/admin/templates/actions.js
@@ -12,15 +12,15 @@ import { revalidatePath } from "next/cache";
 import { redirect } from "@/i18n/navigation";
 import { getServerSession } from "@/lib/auth/get-server-session";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
-import {
-  TemplateSchema,
-  fieldsTextToJson,
-  type TemplateFormState,
-  type TemplateInput,
-} from "@/lib/templates/template-schema";
+import { TemplateSchema, fieldsTextToJson } from "@/lib/templates/template-schema";
 
-function readForm(formData: FormData) {
-  const get = (k: string) => String(formData.get(k) ?? "");
+/** @typedef {import('@/lib/templates/template-schema').TemplateFormState} TemplateFormState */
+/** @typedef {import('@/lib/templates/template-schema').TemplateInput} TemplateInput */
+
+/** @param {FormData} formData */
+function readForm(formData) {
+  /** @param {string} k */
+  const get = (k) => String(formData.get(k) ?? "");
   return {
     name: get("name"),
     title: get("title"),
@@ -30,7 +30,8 @@ function readForm(formData: FormData) {
   };
 }
 
-function toRow(d: TemplateInput) {
+/** @param {TemplateInput} d */
+function toRow(d) {
   return {
     name: d.name,
     title: d.title.trim().length ? d.title.trim() : null,
@@ -40,16 +41,19 @@ function toRow(d: TemplateInput) {
   };
 }
 
-async function finish(): Promise<never> {
+/** @returns {Promise<never>} */
+async function finish() {
   const locale = await getLocale();
   revalidatePath(`/${locale}/admin/templates`);
   return redirect({ href: `/${locale}/admin/templates`, locale });
 }
 
-export async function createTemplateAction(
-  _prev: TemplateFormState,
-  formData: FormData,
-): Promise<TemplateFormState> {
+/**
+ * @param {TemplateFormState} _prev
+ * @param {FormData} formData
+ * @returns {Promise<TemplateFormState>}
+ */
+export async function createTemplateAction(_prev, formData) {
   const t = await getTranslations("admin.templates");
 
   const session = await getServerSession();
@@ -61,7 +65,7 @@ export async function createTemplateAction(
   if (!parsed.success) {
     return {
       status: "error",
-      fieldErrors: parsed.error.flatten().fieldErrors as Record<string, string[]>,
+      fieldErrors: /** @type {Record<string, string[]>} */ (parsed.error.flatten().fieldErrors),
       formError: null,
     };
   }
@@ -84,10 +88,12 @@ export async function createTemplateAction(
   return finish();
 }
 
-export async function updateTemplateAction(
-  _prev: TemplateFormState,
-  formData: FormData,
-): Promise<TemplateFormState> {
+/**
+ * @param {TemplateFormState} _prev
+ * @param {FormData} formData
+ * @returns {Promise<TemplateFormState>}
+ */
+export async function updateTemplateAction(_prev, formData) {
   const t = await getTranslations("admin.templates");
 
   const session = await getServerSession();
@@ -102,7 +108,7 @@ export async function updateTemplateAction(
       status: "error",
       fieldErrors: parsed.success
         ? {}
-        : (parsed.error.flatten().fieldErrors as Record<string, string[]>),
+        : /** @type {Record<string, string[]>} */ (parsed.error.flatten().fieldErrors),
       formError: parsed.success ? t("errorGeneric") : null,
     };
   }
@@ -124,7 +130,11 @@ export async function updateTemplateAction(
   return finish();
 }
 
-export async function deactivateTemplateAction(formData: FormData): Promise<void> {
+/**
+ * @param {FormData} formData
+ * @returns {Promise<void>}
+ */
+export async function deactivateTemplateAction(formData) {
   const session = await getServerSession();
   if (session?.role !== "admin") return;
 
diff --git a/app/[locale]/(app)/admin/templates/new/page.tsx b/app/[locale]/(app)/admin/templates/new/page.jsx
similarity index 78%
rename from app/[locale]/(app)/admin/templates/new/page.tsx
rename to app/[locale]/(app)/admin/templates/new/page.jsx
index 1cc5066..854bda4 100644
--- a/app/[locale]/(app)/admin/templates/new/page.tsx
+++ b/app/[locale]/(app)/admin/templates/new/page.jsx
@@ -4,7 +4,11 @@ import { getTranslations } from "next-intl/server";
 import { TemplateForm } from "../template-form";
 import { createTemplateAction } from "../actions";
 
-export default async function NewTemplatePage({ params }: { params: Promise<{ locale: string }> }) {
+/**
+ * @param {{ params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function NewTemplatePage({ params }) {
   await params;
   const t = await getTranslations("admin.templates");
 
diff --git a/app/[locale]/(app)/admin/templates/page.tsx b/app/[locale]/(app)/admin/templates/page.jsx
similarity index 83%
rename from app/[locale]/(app)/admin/templates/page.tsx
rename to app/[locale]/(app)/admin/templates/page.jsx
index 3eb7346..7c5a862 100644
--- a/app/[locale]/(app)/admin/templates/page.tsx
+++ b/app/[locale]/(app)/admin/templates/page.jsx
@@ -10,7 +10,11 @@ import { createSupabaseServerClient } from "@/lib/supabase/server";
 import { Button } from "@/components/ui/button";
 import { deactivateTemplateAction } from "./actions";
 
-export default async function TemplatesPage({ params }: { params: Promise<{ locale: string }> }) {
+/**
+ * @param {{ params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function TemplatesPage({ params }) {
   const { locale } = await params;
   const t = await getTranslations("admin.templates");
 
@@ -27,7 +31,7 @@ export default async function TemplatesPage({ params }: { params: Promise<{ loca
       <div className="mb-6 flex items-center justify-between gap-4">
         <h1 className="text-foreground text-xl font-semibold">{t("title")}</h1>
         <Button asChild size="lg">
-          <Link href="/admin/templates/new" locale={locale as "vi" | "en"}>
+          <Link href="/admin/templates/new" locale={/** @type {"vi" | "en"} */ (locale)}>
             {t("new")}
           </Link>
         </Button>
@@ -45,7 +49,10 @@ export default async function TemplatesPage({ params }: { params: Promise<{ loca
               </div>
               <div className="flex shrink-0 items-center gap-1">
                 <Button asChild variant="outline">
-                  <Link href={`/admin/templates/${tpl.id}/edit`} locale={locale as "vi" | "en"}>
+                  <Link
+                    href={`/admin/templates/${tpl.id}/edit`}
+                    locale={/** @type {"vi" | "en"} */ (locale)}
+                  >
                     {t("edit")}
                   </Link>
                 </Button>
diff --git a/app/[locale]/(app)/admin/templates/template-form.tsx b/app/[locale]/(app)/admin/templates/template-form.jsx
similarity index 81%
rename from app/[locale]/(app)/admin/templates/template-form.tsx
rename to app/[locale]/(app)/admin/templates/template-form.jsx
index f6ae6d2..73598a0 100644
--- a/app/[locale]/(app)/admin/templates/template-form.tsx
+++ b/app/[locale]/(app)/admin/templates/template-form.jsx
@@ -12,37 +12,40 @@ import { useTranslations } from "next-intl";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
-import { templateGenders, type TemplateFormState } from "@/lib/templates/template-schema";
+import { templateGenders } from "@/lib/templates/template-schema";
 
-export type TemplateDefaults = {
-  id?: number;
-  name: string;
-  title: string;
-  gender: string;
-  photoNum: number;
-  fieldsText: string;
-};
+/** @typedef {import('@/lib/templates/template-schema').TemplateFormState} TemplateFormState */
+
+/**
+ * @typedef {Object} TemplateDefaults
+ * @property {number} [id]
+ * @property {string} name
+ * @property {string} title
+ * @property {string} gender
+ * @property {number} photoNum
+ * @property {string} fieldsText
+ */
 
 const CONTROL =
   "border-input bg-background text-foreground focus-visible:ring-ring w-full rounded-md border px-3 text-sm focus:outline-none focus-visible:ring-2 disabled:opacity-50";
 
-export function TemplateForm({
-  mode,
-  action,
-  defaults,
-}: {
-  mode: "create" | "edit";
-  action: (prev: TemplateFormState, formData: FormData) => Promise<TemplateFormState>;
-  defaults: TemplateDefaults;
-}) {
+/**
+ * @param {{
+ *   mode: "create" | "edit",
+ *   action: (prev: TemplateFormState, formData: FormData) => Promise<TemplateFormState>,
+ *   defaults: TemplateDefaults,
+ * }} props
+ */
+export function TemplateForm({ mode, action, defaults }) {
   const t = useTranslations("admin.templates");
-  const [state, dispatch, isPending] = useActionState<TemplateFormState, FormData>(action, {
+  const [state, dispatch, isPending] = useActionState(action, {
     status: "idle",
   });
 
   const fe = state.status === "error" ? state.fieldErrors : {};
   const formError = state.status === "error" ? state.formError : null;
-  const err = (f: string) =>
+  /** @param {string} f */
+  const err = (f) =>
     fe[f]?.length ? (
       <p className="text-destructive text-sm" role="alert">
         {fe[f][0]}
diff --git a/app/[locale]/(app)/checkups/[id]/imaging/actions.ts b/app/[locale]/(app)/checkups/[id]/imaging/actions.js
similarity index 84%
rename from app/[locale]/(app)/checkups/[id]/imaging/actions.ts
rename to app/[locale]/(app)/checkups/[id]/imaging/actions.js
index 948da1a..beb538a 100644
--- a/app/[locale]/(app)/checkups/[id]/imaging/actions.ts
+++ b/app/[locale]/(app)/checkups/[id]/imaging/actions.js
@@ -18,22 +18,27 @@ import { revalidatePath } from "next/cache";
 
 import { getServerSession } from "@/lib/auth/get-server-session";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
-import type { AppRole } from "@/lib/db/roles";
 import {
   CHECKUP_MEDIA_BUCKET,
   DeleteImageSchema,
   RecordImageSchema,
   isValidStoragePath,
-  type ImageActionState,
 } from "@/lib/imaging/image-schema";
 
-const CLINICAL: AppRole[] = ["admin", "receptionist", "doctor", "nurse"];
-const isClinical = (r: AppRole | null | undefined) => !!r && CLINICAL.includes(r);
+/** @typedef {import('@/lib/db/roles').AppRole} AppRole */
+/** @typedef {import('@/lib/imaging/image-schema').ImageActionState} ImageActionState */
 
-export async function recordImageAction(
-  checkupId: number,
-  storagePath: string,
-): Promise<ImageActionState> {
+/** @type {AppRole[]} */
+const CLINICAL = ["admin", "receptionist", "doctor", "nurse"];
+/** @param {AppRole | null | undefined} r */
+const isClinical = (r) => !!r && CLINICAL.includes(r);
+
+/**
+ * @param {number} checkupId
+ * @param {string} storagePath
+ * @returns {Promise<ImageActionState>}
+ */
+export async function recordImageAction(checkupId, storagePath) {
   const t = await getTranslations("imaging");
 
   const session = await getServerSession();
@@ -65,11 +70,13 @@ export async function recordImageAction(
   return { status: "success" };
 }
 
-export async function deleteImageAction(
-  checkupId: number,
-  imageId: number,
-  storagePath: string,
-): Promise<ImageActionState> {
+/**
+ * @param {number} checkupId
+ * @param {number} imageId
+ * @param {string} storagePath
+ * @returns {Promise<ImageActionState>}
+ */
+export async function deleteImageAction(checkupId, imageId, storagePath) {
   const t = await getTranslations("imaging");
 
   const session = await getServerSession();
diff --git a/app/[locale]/(app)/checkups/[id]/imaging/checkup-barcode.tsx b/app/[locale]/(app)/checkups/[id]/imaging/checkup-barcode.jsx
similarity index 92%
rename from app/[locale]/(app)/checkups/[id]/imaging/checkup-barcode.tsx
rename to app/[locale]/(app)/checkups/[id]/imaging/checkup-barcode.jsx
index e7cdb0e..7a0fc1f 100644
--- a/app/[locale]/(app)/checkups/[id]/imaging/checkup-barcode.tsx
+++ b/app/[locale]/(app)/checkups/[id]/imaging/checkup-barcode.jsx
@@ -14,9 +14,12 @@ import bwipjs from "bwip-js/browser";
 
 import { Button } from "@/components/ui/button";
 
-export function CheckupBarcode({ checkupId }: { checkupId: number }) {
+/**
+ * @param {{ checkupId: number }} props
+ */
+export function CheckupBarcode({ checkupId }) {
   const t = useTranslations("imaging");
-  const canvasRef = useRef<HTMLCanvasElement | null>(null);
+  const canvasRef = useRef(/** @type {HTMLCanvasElement | null} */ (null));
   const [error, setError] = useState(false);
 
   useEffect(() => {
diff --git a/app/[locale]/(app)/checkups/[id]/imaging/image-capture.tsx b/app/[locale]/(app)/checkups/[id]/imaging/image-capture.jsx
similarity index 86%
rename from app/[locale]/(app)/checkups/[id]/imaging/image-capture.tsx
rename to app/[locale]/(app)/checkups/[id]/imaging/image-capture.jsx
index 0478d4c..04b96ec 100644
--- a/app/[locale]/(app)/checkups/[id]/imaging/image-capture.tsx
+++ b/app/[locale]/(app)/checkups/[id]/imaging/image-capture.jsx
@@ -28,18 +28,21 @@ import {
 } from "@/lib/imaging/image-schema";
 import { recordImageAction } from "./actions";
 
-const QUALITY_STEPS = [0.9, 0.8, 0.7, 0.6, 0.5, 0.4] as const;
+/** @type {readonly [0.9, 0.8, 0.7, 0.6, 0.5, 0.4]} */
+const QUALITY_STEPS = [0.9, 0.8, 0.7, 0.6, 0.5, 0.4];
 // Downscale the longest side to this before quality-stepping — a full-res phone
 // photo (e.g. 4000×3000) never fits 200KB on JPEG quality alone, so we must
 // reduce resolution first. 1280px keeps ultrasound/clinic detail legible.
 const MAX_DIMENSION = 1280;
 
-/** Draw a source (video frame or image) onto a canvas scaled to fit MAX_DIMENSION. */
-function makeScaledCanvas(
-  source: CanvasImageSource,
-  w: number,
-  h: number,
-): HTMLCanvasElement | null {
+/**
+ * Draw a source (video frame or image) onto a canvas scaled to fit MAX_DIMENSION.
+ * @param {CanvasImageSource} source
+ * @param {number} w
+ * @param {number} h
+ * @returns {HTMLCanvasElement | null}
+ */
+function makeScaledCanvas(source, w, h) {
   const scale = Math.min(1, MAX_DIMENSION / Math.max(w, h));
   const canvas = document.createElement("canvas");
   canvas.width = Math.max(1, Math.round(w * scale));
@@ -58,13 +61,23 @@ const getCameraSupportSnapshot = () =>
   typeof navigator !== "undefined" && !!navigator.mediaDevices?.getUserMedia;
 const getCameraSupportServerSnapshot = () => false;
 
-function canvasToBlob(canvas: HTMLCanvasElement, quality: number): Promise<Blob | null> {
+/**
+ * @param {HTMLCanvasElement} canvas
+ * @param {number} quality
+ * @returns {Promise<Blob | null>}
+ */
+function canvasToBlob(canvas, quality) {
   return new Promise((resolve) => canvas.toBlob((b) => resolve(b), "image/jpeg", quality));
 }
 
-/** Steps JPEG quality down from 0.9 to 0.4 until the blob fits MAX_IMAGE_BYTES. */
-async function compressToJpeg(canvas: HTMLCanvasElement): Promise<Blob | null> {
-  let smallest: Blob | null = null;
+/**
+ * Steps JPEG quality down from 0.9 to 0.4 until the blob fits MAX_IMAGE_BYTES.
+ * @param {HTMLCanvasElement} canvas
+ * @returns {Promise<Blob | null>}
+ */
+async function compressToJpeg(canvas) {
+  /** @type {Blob | null} */
+  let smallest = null;
   for (const q of QUALITY_STEPS) {
     const blob = await canvasToBlob(canvas, q);
     if (!blob) continue;
@@ -74,12 +87,15 @@ async function compressToJpeg(canvas: HTMLCanvasElement): Promise<Blob | null> {
   return smallest && smallest.size <= MAX_IMAGE_BYTES ? smallest : null;
 }
 
-export function ImageCapture({ checkupId }: { checkupId: number }) {
+/**
+ * @param {{ checkupId: number }} props
+ */
+export function ImageCapture({ checkupId }) {
   const t = useTranslations("imaging");
   const router = useRouter();
 
-  const videoRef = useRef<HTMLVideoElement | null>(null);
-  const streamRef = useRef<MediaStream | null>(null);
+  const videoRef = useRef(/** @type {HTMLVideoElement | null} */ (null));
+  const streamRef = useRef(/** @type {MediaStream | null} */ (null));
 
   // Browser-only feature detection without an Effect: getServerSnapshot
   // returns false so SSR/hydration render the same (no-camera) markup, then
@@ -91,7 +107,7 @@ export function ImageCapture({ checkupId }: { checkupId: number }) {
   );
   const [streaming, setStreaming] = useState(false);
   const [uploading, setUploading] = useState(false);
-  const [error, setError] = useState<string | null>(null);
+  const [error, setError] = useState(/** @type {string | null} */ (null));
 
   // Stop any open camera stream on unmount.
   useEffect(() => {
@@ -122,7 +138,8 @@ export function ImageCapture({ checkupId }: { checkupId: number }) {
     setStreaming(false);
   }
 
-  async function uploadFromCanvas(canvas: HTMLCanvasElement) {
+  /** @param {HTMLCanvasElement} canvas */
+  async function uploadFromCanvas(canvas) {
     setUploading(true);
     setError(null);
     try {
@@ -169,7 +186,8 @@ export function ImageCapture({ checkupId }: { checkupId: number }) {
     void uploadFromCanvas(canvas);
   }
 
-  function handleFileChange(e: React.ChangeEvent<HTMLInputElement>) {
+  /** @param {import("react").ChangeEvent<HTMLInputElement>} e */
+  function handleFileChange(e) {
     const file = e.target.files?.[0];
     e.target.value = ""; // allow re-selecting the same file
     if (!file) return;
diff --git a/app/[locale]/(app)/checkups/[id]/imaging/image-gallery.tsx b/app/[locale]/(app)/checkups/[id]/imaging/image-gallery.jsx
similarity index 84%
rename from app/[locale]/(app)/checkups/[id]/imaging/image-gallery.tsx
rename to app/[locale]/(app)/checkups/[id]/imaging/image-gallery.jsx
index 39503f0..d1ec714 100644
--- a/app/[locale]/(app)/checkups/[id]/imaging/image-gallery.tsx
+++ b/app/[locale]/(app)/checkups/[id]/imaging/image-gallery.jsx
@@ -15,16 +15,20 @@ import { useTranslations } from "next-intl";
 import { Button } from "@/components/ui/button";
 import { deleteImageAction } from "./actions";
 
-type GalleryImage = { id: number; storagePath: string; url: string | null };
+/** @typedef {{ id: number, storagePath: string, url: string | null }} GalleryImage */
 
-export function ImageGallery({ checkupId, images }: { checkupId: number; images: GalleryImage[] }) {
+/**
+ * @param {{ checkupId: number, images: GalleryImage[] }} props
+ */
+export function ImageGallery({ checkupId, images }) {
   const t = useTranslations("imaging");
   const router = useRouter();
   const [isPending, startTransition] = useTransition();
-  const [pendingId, setPendingId] = useState<number | null>(null);
-  const [error, setError] = useState<string | null>(null);
+  const [pendingId, setPendingId] = useState(/** @type {number | null} */ (null));
+  const [error, setError] = useState(/** @type {string | null} */ (null));
 
-  function handleDelete(image: GalleryImage) {
+  /** @param {GalleryImage} image */
+  function handleDelete(image) {
     setError(null);
     setPendingId(image.id);
     startTransition(async () => {
diff --git a/app/[locale]/(app)/checkups/[id]/imaging/page.tsx b/app/[locale]/(app)/checkups/[id]/imaging/page.jsx
similarity index 94%
rename from app/[locale]/(app)/checkups/[id]/imaging/page.tsx
rename to app/[locale]/(app)/checkups/[id]/imaging/page.jsx
index 4a37792..fd18756 100644
--- a/app/[locale]/(app)/checkups/[id]/imaging/page.tsx
+++ b/app/[locale]/(app)/checkups/[id]/imaging/page.jsx
@@ -18,11 +18,11 @@ import { ImageCapture } from "./image-capture";
 import { ImageGallery } from "./image-gallery";
 import { CheckupBarcode } from "./checkup-barcode";
 
-export default async function ImagingPage({
-  params,
-}: {
-  params: Promise<{ locale: string; id: string }>;
-}) {
+/**
+ * @param {{ params: Promise<{ locale: string, id: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function ImagingPage({ params }) {
   const { locale, id } = await params;
   const t = await getTranslations("imaging");
   const tReports = await getTranslations("reports");
diff --git a/app/[locale]/(app)/checkups/[id]/invoice/route.ts b/app/[locale]/(app)/checkups/[id]/invoice/route.js
similarity index 89%
rename from app/[locale]/(app)/checkups/[id]/invoice/route.ts
rename to app/[locale]/(app)/checkups/[id]/invoice/route.js
index ff9343f..61f0ee1 100644
--- a/app/[locale]/(app)/checkups/[id]/invoice/route.ts
+++ b/app/[locale]/(app)/checkups/[id]/invoice/route.js
@@ -7,16 +7,19 @@
 import { getTranslations } from "next-intl/server";
 import { getServerSession } from "@/lib/auth/get-server-session";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
-import { renderInvoicePdf, type InvoiceLine } from "@/lib/pdf/invoice-document";
+import { renderInvoicePdf } from "@/lib/pdf/invoice-document";
 import { sumLineTotals } from "@/lib/billing/totals";
 
+/** @typedef {import('@/lib/pdf/invoice-document').InvoiceLine} InvoiceLine */
+
 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
 
-export async function GET(
-  _req: Request,
-  { params }: { params: Promise<{ locale: string; id: string }> },
-) {
+/**
+ * @param {Request} _req
+ * @param {{ params: Promise<{ locale: string, id: string }> }} context
+ */
+export async function GET(_req, { params }) {
   const { id } = await params;
   const checkupId = Number(id);
   if (!Number.isFinite(checkupId)) return new Response("Not found", { status: 404 });
@@ -69,13 +72,15 @@ export async function GET(
   const medName = new Map((meds ?? []).map((m) => [m.id, m.name]));
   const svcName = new Map((services ?? []).map((x) => [x.id, x.name]));
 
-  const medicines: InvoiceLine[] = (items ?? []).map((i) => ({
+  /** @type {InvoiceLine[]} */
+  const medicines = (items ?? []).map((i) => ({
     name: medName.get(i.medicine_id) ?? "—",
     quantity: i.quantity,
     unitPrice: i.unit_price,
     lineTotal: i.line_total,
   }));
-  const serviceLines: InvoiceLine[] = (svcs ?? []).map((x) => ({
+  /** @type {InvoiceLine[]} */
+  const serviceLines = (svcs ?? []).map((x) => ({
     name: svcName.get(x.service_id) ?? "—",
     quantity: x.quantity,
     unitPrice: x.unit_price,
diff --git a/app/[locale]/(app)/checkups/[id]/page.tsx b/app/[locale]/(app)/checkups/[id]/page.jsx
similarity index 84%
rename from app/[locale]/(app)/checkups/[id]/page.tsx
rename to app/[locale]/(app)/checkups/[id]/page.jsx
index 9e2659b..61344b2 100644
--- a/app/[locale]/(app)/checkups/[id]/page.tsx
+++ b/app/[locale]/(app)/checkups/[id]/page.jsx
@@ -9,13 +9,14 @@ import { Button } from "@/components/ui/button";
 import { CheckupForm } from "../checkup-form";
 import { DeleteCheckupButton } from "../delete-checkup-button";
 
-const str = (v: string | number | null) => (v == null ? "" : String(v));
+/** @param {string | number | null} v */
+const str = (v) => (v == null ? "" : String(v));
 
-export default async function CheckupPage({
-  params,
-}: {
-  params: Promise<{ locale: string; id: string }>;
-}) {
+/**
+ * @param {{ params: Promise<{ locale: string, id: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function CheckupPage({ params }) {
   const { locale, id } = await params;
   const t = await getTranslations("checkups");
   const tBilling = await getTranslations("billing");
@@ -58,7 +59,9 @@ export default async function CheckupPage({
   // De-dupe + trim recent diagnoses for the quick-pick, capped at 50 entries.
   const diagnosisSuggestions = [
     ...new Set(
-      (recentDiagnoses ?? []).map((r) => r.diagnosis?.trim()).filter((d): d is string => !!d),
+      (recentDiagnoses ?? [])
+        .map((r) => r.diagnosis?.trim())
+        .filter(/** @returns {d is string} */ (d) => !!d),
     ),
   ].slice(0, 50);
 
@@ -71,8 +74,11 @@ export default async function CheckupPage({
     : (templates ?? []);
 
   const templateValues = Array.isArray(c.template_values)
-    ? (c.template_values as unknown[])
-        .filter((v): v is { label: unknown; value: unknown } => !!v && typeof v === "object")
+    ? /** @type {unknown[]} */ (c.template_values)
+        .filter(
+          /** @returns {v is { label: unknown, value: unknown }} */
+          (v) => !!v && typeof v === "object",
+        )
         .map((v) => ({ label: String(v.label ?? ""), value: String(v.value ?? "") }))
     : [];
 
@@ -102,12 +108,15 @@ export default async function CheckupPage({
         </div>
         <div className="flex gap-2">
           <Button asChild variant="outline">
-            <Link href={`/checkups/${c.id}/prescription`} locale={locale as "vi" | "en"}>
+            <Link
+              href={`/checkups/${c.id}/prescription`}
+              locale={/** @type {"vi" | "en"} */ (locale)}
+            >
               {tBilling("title")}
             </Link>
           </Button>
           <Button asChild variant="outline">
-            <Link href={`/checkups/${c.id}/imaging`} locale={locale as "vi" | "en"}>
+            <Link href={`/checkups/${c.id}/imaging`} locale={/** @type {"vi" | "en"} */ (locale)}>
               {tImaging("title")}
             </Link>
           </Button>
diff --git a/app/[locale]/(app)/checkups/[id]/prescription/actions.ts b/app/[locale]/(app)/checkups/[id]/prescription/actions.js
similarity index 76%
rename from app/[locale]/(app)/checkups/[id]/prescription/actions.ts
rename to app/[locale]/(app)/checkups/[id]/prescription/actions.js
index 7e74f36..0a808ad 100644
--- a/app/[locale]/(app)/checkups/[id]/prescription/actions.ts
+++ b/app/[locale]/(app)/checkups/[id]/prescription/actions.js
@@ -16,35 +16,47 @@ import { revalidatePath } from "next/cache";
 import { redirect } from "@/i18n/navigation";
 import { getServerSession } from "@/lib/auth/get-server-session";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
-import type { AppRole } from "@/lib/db/roles";
 import {
   MedicineLinesSchema,
   ServiceLinesSchema,
   MarkPaidSchema,
-  type PrescriptionSaveState,
-  type MarkPaidState,
 } from "@/lib/billing/prescription-schema";
 
-const CLINICAL: AppRole[] = ["admin", "receptionist", "doctor", "nurse"];
-const BILLING: AppRole[] = ["admin", "cashier"];
-const isClinical = (r: AppRole | null | undefined) => !!r && CLINICAL.includes(r);
-const isBilling = (r: AppRole | null | undefined) => !!r && BILLING.includes(r);
+/** @typedef {import('@/lib/db/roles').AppRole} AppRole */
+/** @typedef {import('@/lib/billing/prescription-schema').PrescriptionSaveState} PrescriptionSaveState */
+/** @typedef {import('@/lib/billing/prescription-schema').MarkPaidState} MarkPaidState */
 
-/** Parses a JSON-array form field; returns [] on any malformed input. */
-function parseJsonArray(raw: FormDataEntryValue | null): unknown[] {
+/** @type {AppRole[]} */
+const CLINICAL = ["admin", "receptionist", "doctor", "nurse"];
+/** @type {AppRole[]} */
+const BILLING = ["admin", "cashier"];
+/** @param {AppRole | null | undefined} r */
+const isClinical = (r) => !!r && CLINICAL.includes(r);
+/** @param {AppRole | null | undefined} r */
+const isBilling = (r) => !!r && BILLING.includes(r);
+
+/**
+ * Parses a JSON-array form field; returns [] on any malformed input.
+ * @param {FormDataEntryValue | null} raw
+ * @returns {unknown[]}
+ */
+function parseJsonArray(raw) {
   if (typeof raw !== "string") return [];
   try {
-    const v: unknown = JSON.parse(raw);
+    /** @type {unknown} */
+    const v = JSON.parse(raw);
     return Array.isArray(v) ? v : [];
   } catch {
     return [];
   }
 }
 
-export async function savePrescriptionAction(
-  _prev: PrescriptionSaveState,
-  formData: FormData,
-): Promise<PrescriptionSaveState> {
+/**
+ * @param {PrescriptionSaveState} _prev
+ * @param {FormData} formData
+ * @returns {Promise<PrescriptionSaveState>}
+ */
+export async function savePrescriptionAction(_prev, formData) {
   const t = await getTranslations("billing");
 
   const session = await getServerSession();
@@ -95,10 +107,12 @@ export async function savePrescriptionAction(
   return redirect({ href: `/${locale}/checkups/${checkupId}`, locale });
 }
 
-export async function markPaidAction(
-  _prev: MarkPaidState,
-  formData: FormData,
-): Promise<MarkPaidState> {
+/**
+ * @param {MarkPaidState} _prev
+ * @param {FormData} formData
+ * @returns {Promise<MarkPaidState>}
+ */
+export async function markPaidAction(_prev, formData) {
   const t = await getTranslations("billing");
 
   const session = await getServerSession();
diff --git a/app/[locale]/(app)/checkups/[id]/prescription/page.tsx b/app/[locale]/(app)/checkups/[id]/prescription/page.jsx
similarity index 95%
rename from app/[locale]/(app)/checkups/[id]/prescription/page.tsx
rename to app/[locale]/(app)/checkups/[id]/prescription/page.jsx
index 45f40e5..8bde153 100644
--- a/app/[locale]/(app)/checkups/[id]/prescription/page.tsx
+++ b/app/[locale]/(app)/checkups/[id]/prescription/page.jsx
@@ -16,11 +16,11 @@ import { Button } from "@/components/ui/button";
 import { routing } from "@/i18n/routing";
 import { PrescriptionComposer } from "./prescription-composer";
 
-export default async function PrescriptionPage({
-  params,
-}: {
-  params: Promise<{ locale: string; id: string }>;
-}) {
+/**
+ * @param {{ params: Promise<{ locale: string, id: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function PrescriptionPage({ params }) {
   const { locale, id } = await params;
   const t = await getTranslations("billing");
   const tReports = await getTranslations("reports");
diff --git a/app/[locale]/(app)/checkups/[id]/prescription/pdf/route.ts b/app/[locale]/(app)/checkups/[id]/prescription/pdf/route.js
similarity index 90%
rename from app/[locale]/(app)/checkups/[id]/prescription/pdf/route.ts
rename to app/[locale]/(app)/checkups/[id]/prescription/pdf/route.js
index 48ebac5..649aa5f 100644
--- a/app/[locale]/(app)/checkups/[id]/prescription/pdf/route.ts
+++ b/app/[locale]/(app)/checkups/[id]/prescription/pdf/route.js
@@ -9,18 +9,18 @@ import { getTranslations } from "next-intl/server";
 import { getServerSession } from "@/lib/auth/get-server-session";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
 import { computeAge } from "@/lib/pdf/patient-info";
-import {
-  renderPrescriptionPdf,
-  type PrescriptionMedicineLine,
-} from "@/lib/pdf/prescription-document";
+import { renderPrescriptionPdf } from "@/lib/pdf/prescription-document";
+
+/** @typedef {import('@/lib/pdf/prescription-document').PrescriptionMedicineLine} PrescriptionMedicineLine */
 
 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
 
-export async function GET(
-  _req: Request,
-  { params }: { params: Promise<{ locale: string; id: string }> },
-) {
+/**
+ * @param {Request} _req
+ * @param {{ params: Promise<{ locale: string, id: string }> }} context
+ */
+export async function GET(_req, { params }) {
   const { id } = await params;
   const checkupId = Number(id);
   if (!Number.isFinite(checkupId)) return new Response("Not found", { status: 404 });
@@ -71,7 +71,8 @@ export async function GET(
     : { data: [] };
   const medById = new Map((meds ?? []).map((m) => [m.id, m]));
 
-  const medicines: PrescriptionMedicineLine[] = (items ?? []).map((i) => {
+  /** @type {PrescriptionMedicineLine[]} */
+  const medicines = (items ?? []).map((i) => {
     const med = medById.get(i.medicine_id);
     return {
       name: med?.name ?? "—",
diff --git a/app/[locale]/(app)/checkups/[id]/prescription/prescription-composer.tsx b/app/[locale]/(app)/checkups/[id]/prescription/prescription-composer.jsx
similarity index 81%
rename from app/[locale]/(app)/checkups/[id]/prescription/prescription-composer.tsx
rename to app/[locale]/(app)/checkups/[id]/prescription/prescription-composer.jsx
index c1a7a71..1a9e68f 100644
--- a/app/[locale]/(app)/checkups/[id]/prescription/prescription-composer.tsx
+++ b/app/[locale]/(app)/checkups/[id]/prescription/prescription-composer.jsx
@@ -18,38 +18,51 @@ import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
 import { dosePresets } from "@/lib/billing/dose-presets";
-import {
-  paymentMethods,
-  type MarkPaidState,
-  type PrescriptionSaveState,
-} from "@/lib/billing/prescription-schema";
+import { paymentMethods } from "@/lib/billing/prescription-schema";
 import { markPaidAction, savePrescriptionAction } from "./actions";
 
+/** @typedef {import('@/lib/billing/prescription-schema').MarkPaidState} MarkPaidState */
+/** @typedef {import('@/lib/billing/prescription-schema').PrescriptionSaveState} PrescriptionSaveState */
+
 const DOSE_PRESETS_LIST_ID = "dose-presets";
 
-const vnd = (n: number) => `${new Intl.NumberFormat("vi-VN").format(n)} ₫`;
+/** @param {number} n */
+const vnd = (n) => `${new Intl.NumberFormat("vi-VN").format(n)} ₫`;
 
 const SELECT =
   "border-input bg-background text-foreground focus-visible:ring-ring h-10 w-full rounded-md border px-3 text-sm focus:outline-none focus-visible:ring-2 disabled:opacity-50";
 
-type Medicine = { id: number; name: string; unit: string | null; sale_price: number };
-type Service = { id: number; name: string; price: number };
+/** @typedef {{ id: number, name: string, unit: string | null, sale_price: number }} Medicine */
+/** @typedef {{ id: number, name: string, price: number }} Service */
 
-type MedicineRow = {
-  key: string;
-  medicineId: number;
-  quantity: number;
-  dosage: string;
-  notes: string;
-};
-type ServiceRow = { key: string; serviceId: number; quantity: number };
+/**
+ * @typedef {object} MedicineRow
+ * @property {string} key
+ * @property {number} medicineId
+ * @property {number} quantity
+ * @property {string} dosage
+ * @property {string} notes
+ */
+/** @typedef {{ key: string, serviceId: number, quantity: number }} ServiceRow */
 
-type Payment = {
-  status: "unpaid" | "paid";
-  method: string | null;
-  paidAt: string | null;
-};
+/**
+ * @typedef {object} Payment
+ * @property {"unpaid" | "paid"} status
+ * @property {string | null} method
+ * @property {string | null} paidAt
+ */
 
+/**
+ * @param {{
+ *   checkupId: number,
+ *   medicines: Medicine[],
+ *   services: Service[],
+ *   initialMedicineLines: { medicineId: number, quantity: number, dosage: string, notes: string }[],
+ *   initialServiceLines: { serviceId: number, quantity: number }[],
+ *   payment: Payment,
+ *   canMarkPaid: boolean,
+ * }} props
+ */
 export function PrescriptionComposer({
   checkupId,
   medicines,
@@ -58,34 +71,24 @@ export function PrescriptionComposer({
   initialServiceLines,
   payment,
   canMarkPaid,
-}: {
-  checkupId: number;
-  medicines: Medicine[];
-  services: Service[];
-  initialMedicineLines: { medicineId: number; quantity: number; dosage: string; notes: string }[];
-  initialServiceLines: { serviceId: number; quantity: number }[];
-  payment: Payment;
-  canMarkPaid: boolean;
 }) {
   const t = useTranslations("billing");
 
-  const [medicineRows, setMedicineRows] = useState<MedicineRow[]>(() =>
-    initialMedicineLines.map((l, i) => ({ ...l, key: `m-init-${i}` })),
+  const [medicineRows, setMedicineRows] = useState(
+    /** @type {MedicineRow[]} */ (
+      initialMedicineLines.map((l, i) => ({ ...l, key: `m-init-${i}` }))
+    ),
   );
-  const [serviceRows, setServiceRows] = useState<ServiceRow[]>(() =>
-    initialServiceLines.map((l, i) => ({ ...l, key: `s-init-${i}` })),
+  const [serviceRows, setServiceRows] = useState(
+    /** @type {ServiceRow[]} */ (initialServiceLines.map((l, i) => ({ ...l, key: `s-init-${i}` }))),
   );
 
-  const [saveState, saveDispatch, isSaving] = useActionState<PrescriptionSaveState, FormData>(
-    savePrescriptionAction,
-    { status: "idle" },
-  );
-  const [payState, payDispatch, isPaying] = useActionState<MarkPaidState, FormData>(
-    markPaidAction,
-    {
-      status: "idle",
-    },
-  );
+  const [saveState, saveDispatch, isSaving] = useActionState(savePrescriptionAction, {
+    status: "idle",
+  });
+  const [payState, payDispatch, isPaying] = useActionState(markPaidAction, {
+    status: "idle",
+  });
 
   const medMap = new Map(medicines.map((m) => [m.id, m.sale_price]));
   const svcMap = new Map(services.map((s) => [s.id, s.price]));
@@ -101,26 +104,32 @@ export function PrescriptionComposer({
         notes: "",
       },
     ]);
-  const removeMedicineRow = (key: string) =>
-    setMedicineRows((rows) => rows.filter((r) => r.key !== key));
-  const updateMedicineRow = <K extends keyof MedicineRow>(
-    key: string,
-    field: K,
-    value: MedicineRow[K],
-  ) => setMedicineRows((rows) => rows.map((r) => (r.key === key ? { ...r, [field]: value } : r)));
+  /** @param {string} key */
+  const removeMedicineRow = (key) => setMedicineRows((rows) => rows.filter((r) => r.key !== key));
+  /**
+   * @template {keyof MedicineRow} K
+   * @param {string} key
+   * @param {K} field
+   * @param {MedicineRow[K]} value
+   */
+  const updateMedicineRow = (key, field, value) =>
+    setMedicineRows((rows) => rows.map((r) => (r.key === key ? { ...r, [field]: value } : r)));
 
   const addServiceRow = () =>
     setServiceRows((rows) => [
       ...rows,
       { key: `s-${crypto.randomUUID()}`, serviceId: services[0]?.id ?? 0, quantity: 1 },
     ]);
-  const removeServiceRow = (key: string) =>
-    setServiceRows((rows) => rows.filter((r) => r.key !== key));
-  const updateServiceRow = <K extends keyof ServiceRow>(
-    key: string,
-    field: K,
-    value: ServiceRow[K],
-  ) => setServiceRows((rows) => rows.map((r) => (r.key === key ? { ...r, [field]: value } : r)));
+  /** @param {string} key */
+  const removeServiceRow = (key) => setServiceRows((rows) => rows.filter((r) => r.key !== key));
+  /**
+   * @template {keyof ServiceRow} K
+   * @param {string} key
+   * @param {K} field
+   * @param {ServiceRow[K]} value
+   */
+  const updateServiceRow = (key, field, value) =>
+    setServiceRows((rows) => rows.map((r) => (r.key === key ? { ...r, [field]: value } : r)));
 
   const medicineTotal = medicineRows.reduce(
     (sum, r) => sum + (medMap.get(r.medicineId) ?? 0) * (r.quantity || 0),
diff --git a/app/[locale]/(app)/checkups/[id]/report/route.ts b/app/[locale]/(app)/checkups/[id]/report/route.js
similarity index 78%
rename from app/[locale]/(app)/checkups/[id]/report/route.ts
rename to app/[locale]/(app)/checkups/[id]/report/route.js
index f6dcc6a..3d944b8 100644
--- a/app/[locale]/(app)/checkups/[id]/report/route.ts
+++ b/app/[locale]/(app)/checkups/[id]/report/route.js
@@ -14,17 +14,20 @@ import { getServerSession } from "@/lib/auth/get-server-session";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
 import { CHECKUP_MEDIA_BUCKET, SIGNED_URL_TTL_SECONDS } from "@/lib/imaging/image-schema";
 import { computeAge } from "@/lib/pdf/patient-info";
-import { renderUltrasoundPdf, type UltrasoundImage } from "@/lib/pdf/ultrasound-document";
+import { renderUltrasoundPdf } from "@/lib/pdf/ultrasound-document";
+
+/** @typedef {import('@/lib/pdf/ultrasound-document').UltrasoundImage} UltrasoundImage */
 
 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
 
 const MAX_REPORT_IMAGES = 4;
 
-export async function GET(
-  _req: Request,
-  { params }: { params: Promise<{ locale: string; id: string }> },
-) {
+/**
+ * @param {Request} _req
+ * @param {{ params: Promise<{ locale: string, id: string }> }} context
+ */
+export async function GET(_req, { params }) {
   const { id } = await params;
   const checkupId = Number(id);
   if (!Number.isFinite(checkupId)) return new Response("Not found", { status: 404 });
@@ -75,23 +78,27 @@ export async function GET(
   const tPatients = await getTranslations("patients");
 
   const downloaded = await Promise.all(
-    (images ?? []).map(async (img): Promise<UltrasoundImage | null> => {
-      const { data: signed } = await supabase.storage
-        .from(CHECKUP_MEDIA_BUCKET)
-        .createSignedUrl(img.storage_path, SIGNED_URL_TTL_SECONDS);
-      if (!signed?.signedUrl) return null;
-      try {
-        const res = await fetch(signed.signedUrl);
-        if (!res.ok) return null;
-        const arrayBuffer = await res.arrayBuffer();
-        return { data: Buffer.from(arrayBuffer), format: "jpg" };
-      } catch {
-        return null;
-      }
-    }),
+    (images ?? []).map(
+      /** @returns {Promise<UltrasoundImage | null>} */
+      async (img) => {
+        const { data: signed } = await supabase.storage
+          .from(CHECKUP_MEDIA_BUCKET)
+          .createSignedUrl(img.storage_path, SIGNED_URL_TTL_SECONDS);
+        if (!signed?.signedUrl) return null;
+        try {
+          const res = await fetch(signed.signedUrl);
+          if (!res.ok) return null;
+          const arrayBuffer = await res.arrayBuffer();
+          return { data: Buffer.from(arrayBuffer), format: "jpg" };
+        } catch {
+          return null;
+        }
+      },
+    ),
   );
-  const reportImages: UltrasoundImage[] = downloaded.filter(
-    (img): img is UltrasoundImage => img != null,
+  /** @type {UltrasoundImage[]} */
+  const reportImages = downloaded.filter(
+    /** @returns {img is UltrasoundImage} */ (img) => img != null,
   );
 
   const buffer = await renderUltrasoundPdf({
diff --git a/app/[locale]/(app)/checkups/actions.ts b/app/[locale]/(app)/checkups/actions.js
similarity index 77%
rename from app/[locale]/(app)/checkups/actions.ts
rename to app/[locale]/(app)/checkups/actions.js
index 6cd6def..b345c1b 100644
--- a/app/[locale]/(app)/checkups/actions.ts
+++ b/app/[locale]/(app)/checkups/actions.js
@@ -12,22 +12,24 @@ import { revalidatePath } from "next/cache";
 import { redirect } from "@/i18n/navigation";
 import { getServerSession } from "@/lib/auth/get-server-session";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
-import type { AppRole } from "@/lib/db/roles";
-import {
-  CheckupSaveSchema,
-  parseNum,
-  parseTemplateValues,
-  type CheckupSaveState,
-} from "@/lib/checkups/checkup-schema";
+import { CheckupSaveSchema, parseNum, parseTemplateValues } from "@/lib/checkups/checkup-schema";
 
-const CLINICAL: AppRole[] = ["admin", "receptionist", "doctor", "nurse"];
-const isClinical = (r: AppRole | null | undefined) => !!r && CLINICAL.includes(r);
-const nullIfBlank = (s: string) => (s.trim().length ? s.trim() : null);
+/** @typedef {import('@/lib/db/roles').AppRole} AppRole */
+/** @typedef {import('@/lib/checkups/checkup-schema').CheckupSaveState} CheckupSaveState */
 
-export async function saveCheckupAction(
-  _prev: CheckupSaveState,
-  formData: FormData,
-): Promise<CheckupSaveState> {
+/** @type {AppRole[]} */
+const CLINICAL = ["admin", "receptionist", "doctor", "nurse"];
+/** @param {AppRole | null | undefined} r */
+const isClinical = (r) => !!r && CLINICAL.includes(r);
+/** @param {string} s */
+const nullIfBlank = (s) => (s.trim().length ? s.trim() : null);
+
+/**
+ * @param {CheckupSaveState} _prev
+ * @param {FormData} formData
+ * @returns {Promise<CheckupSaveState>}
+ */
+export async function saveCheckupAction(_prev, formData) {
   const t = await getTranslations("checkups");
 
   const session = await getServerSession();
@@ -36,7 +38,8 @@ export async function saveCheckupAction(
   }
 
   const id = Number(formData.get("id"));
-  const get = (k: string) => String(formData.get(k) ?? "");
+  /** @param {string} k */
+  const get = (k) => String(formData.get(k) ?? "");
   const parsed = CheckupSaveSchema.safeParse({
     heartBeat: get("heartBeat"),
     bloodPressure: get("bloodPressure"),
@@ -56,7 +59,7 @@ export async function saveCheckupAction(
       status: "error",
       fieldErrors: parsed.success
         ? {}
-        : (parsed.error.flatten().fieldErrors as Record<string, string[]>),
+        : /** @type {Record<string, string[]>} */ (parsed.error.flatten().fieldErrors),
       formError: parsed.success ? t("errorGeneric") : null,
     };
   }
@@ -104,7 +107,11 @@ export async function saveCheckupAction(
 }
 
 // ── Soft-delete ───────────────────────────────────────────────────────────────
-export async function deleteCheckupAction(formData: FormData): Promise<void> {
+/**
+ * @param {FormData} formData
+ * @returns {Promise<void>}
+ */
+export async function deleteCheckupAction(formData) {
   const session = await getServerSession();
   if (!isClinical(session?.role)) return;
 
diff --git a/app/[locale]/(app)/checkups/checkup-form.tsx b/app/[locale]/(app)/checkups/checkup-form.jsx
similarity index 81%
rename from app/[locale]/(app)/checkups/checkup-form.tsx
rename to app/[locale]/(app)/checkups/checkup-form.jsx
index 770ce98..36c119b 100644
--- a/app/[locale]/(app)/checkups/checkup-form.tsx
+++ b/app/[locale]/(app)/checkups/checkup-form.jsx
@@ -6,56 +6,59 @@
  * (redirects to the queue on success).
  */
 
-import { useActionState, useEffect, useRef, useState, type RefObject } from "react";
+import { useActionState, useEffect, useRef, useState } from "react";
 import { useTranslations } from "next-intl";
 
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
-import { checkupStatuses, type CheckupSaveState } from "@/lib/checkups/checkup-schema";
+import { checkupStatuses } from "@/lib/checkups/checkup-schema";
 import { saveCheckupAction } from "./actions";
 
+/** @typedef {import('@/lib/checkups/checkup-schema').CheckupSaveState} CheckupSaveState */
+
 const CONTROL =
   "border-input bg-background text-foreground focus-visible:ring-ring w-full rounded-md border px-3 text-sm focus:outline-none focus-visible:ring-2 disabled:opacity-50";
 
-export type CheckupDefaults = {
-  id: number;
-  heartBeat: string;
-  bloodPressure: string;
-  temperature: string;
-  weight: string;
-  height: string;
-  symptoms: string;
-  diagnosis: string;
-  conclusion: string;
-  notes: string;
-  recheckDate: string;
-  status: string;
-};
+/**
+ * @typedef {object} CheckupDefaults
+ * @property {number} id
+ * @property {string} heartBeat
+ * @property {string} bloodPressure
+ * @property {string} temperature
+ * @property {string} weight
+ * @property {string} height
+ * @property {string} symptoms
+ * @property {string} diagnosis
+ * @property {string} conclusion
+ * @property {string} notes
+ * @property {string} recheckDate
+ * @property {string} status
+ */
 
-export type CheckupTemplateOption = { id: number; name: string; labels: string[] };
-type TemplateValue = { label: string; value: string };
+/** @typedef {{ id: number, name: string, labels: string[] }} CheckupTemplateOption */
+/** @typedef {{ label: string, value: string }} TemplateValue */
 
+/**
+ * @param {{
+ *   defaults: CheckupDefaults,
+ *   templates: CheckupTemplateOption[],
+ *   initialTemplateId: number | null,
+ *   initialTemplateValues: TemplateValue[],
+ *   diagnosisSuggestions?: string[],
+ * }} props
+ */
 export function CheckupForm({
   defaults,
   templates,
   initialTemplateId,
   initialTemplateValues,
   diagnosisSuggestions = [],
-}: {
-  defaults: CheckupDefaults;
-  templates: CheckupTemplateOption[];
-  initialTemplateId: number | null;
-  initialTemplateValues: TemplateValue[];
-  diagnosisSuggestions?: string[];
 }) {
   const t = useTranslations("checkups");
-  const [state, dispatch, isPending] = useActionState<CheckupSaveState, FormData>(
-    saveCheckupAction,
-    {
-      status: "idle",
-    },
-  );
+  const [state, dispatch, isPending] = useActionState(saveCheckupAction, {
+    status: "idle",
+  });
   const formError = state.status === "error" ? state.formError : null;
 
   // Unsaved-changes guard: any edit flips `dirty`; saving clears it so a
@@ -63,11 +66,12 @@ export function CheckupForm({
   // beforeunload doesn't fire for client-side route changes, so we also show
   // an in-app marker near the Save button.
   const [dirty, setDirty] = useState(false);
-  const diagnosisRef = useRef<HTMLTextAreaElement>(null);
+  const diagnosisRef = useRef(/** @type {HTMLTextAreaElement | null} */ (null));
 
   useEffect(() => {
     if (!dirty || isPending) return;
-    function onBeforeUnload(e: BeforeUnloadEvent) {
+    /** @param {BeforeUnloadEvent} e */
+    function onBeforeUnload(e) {
       e.preventDefault();
       e.returnValue = "";
     }
@@ -80,7 +84,8 @@ export function CheckupForm({
   // appends the chosen text into the (uncontrolled) textarea via ref — the
   // least disruptive option since it doesn't require converting the field to
   // controlled state.
-  function applyDiagnosisSuggestion(text: string) {
+  /** @param {string} text */
+  function applyDiagnosisSuggestion(text) {
     if (!text) return;
     const el = diagnosisRef.current;
     if (!el) return;
@@ -95,8 +100,10 @@ export function CheckupForm({
   const [templateId, setTemplateId] = useState(
     initialTemplateId != null ? String(initialTemplateId) : "",
   );
-  const [templateFieldValues, setTemplateFieldValues] = useState<Record<string, string>>(() =>
-    Object.fromEntries(initialTemplateValues.map((v) => [v.label, v.value])),
+  const [templateFieldValues, setTemplateFieldValues] = useState(
+    /** @type {Record<string, string>} */ (
+      Object.fromEntries(initialTemplateValues.map((v) => [v.label, v.value]))
+    ),
   );
 
   const selectedTemplate = templates.find((tpl) => String(tpl.id) === templateId) ?? null;
@@ -107,18 +114,23 @@ export function CheckupForm({
     })),
   );
 
-  const textField = (name: keyof CheckupDefaults, label: string) => (
+  /**
+   * @param {keyof CheckupDefaults} name
+   * @param {string} label
+   */
+  const textField = (name, label) => (
     <div className="space-y-1.5">
       <Label htmlFor={name}>{label}</Label>
       <Input id={name} name={name} defaultValue={defaults[name]} disabled={isPending} />
     </div>
   );
 
-  const area = (
-    name: keyof CheckupDefaults,
-    label: string,
-    ref?: RefObject<HTMLTextAreaElement | null>,
-  ) => (
+  /**
+   * @param {keyof CheckupDefaults} name
+   * @param {string} label
+   * @param {import("react").RefObject<HTMLTextAreaElement | null>} [ref]
+   */
+  const area = (name, label, ref) => (
     <div className="space-y-1.5">
       <Label htmlFor={name}>{label}</Label>
       <textarea
diff --git a/app/[locale]/(app)/checkups/delete-checkup-button.tsx b/app/[locale]/(app)/checkups/delete-checkup-button.jsx
similarity index 80%
rename from app/[locale]/(app)/checkups/delete-checkup-button.tsx
rename to app/[locale]/(app)/checkups/delete-checkup-button.jsx
index bdbd02c..777eae8 100644
--- a/app/[locale]/(app)/checkups/delete-checkup-button.tsx
+++ b/app/[locale]/(app)/checkups/delete-checkup-button.jsx
@@ -6,16 +6,19 @@
  * window.confirm(), and cancels (preventDefault) if the user declines.
  */
 
-import type { FormEvent } from "react";
 import { useTranslations } from "next-intl";
 
 import { Button } from "@/components/ui/button";
 import { deleteCheckupAction } from "./actions";
 
-export function DeleteCheckupButton({ checkupId }: { checkupId: number }) {
+/**
+ * @param {{ checkupId: number }} props
+ */
+export function DeleteCheckupButton({ checkupId }) {
   const t = useTranslations("checkups");
 
-  function onSubmit(e: FormEvent<HTMLFormElement>) {
+  /** @param {import("react").FormEvent<HTMLFormElement>} e */
+  function onSubmit(e) {
     if (!window.confirm(t("confirmDelete"))) {
       e.preventDefault();
     }
diff --git a/app/[locale]/(app)/reminders/layout.tsx b/app/[locale]/(app)/checkups/layout.jsx
similarity index 55%
rename from app/[locale]/(app)/reminders/layout.tsx
rename to app/[locale]/(app)/checkups/layout.jsx
index 8c09de6..1cc4c50 100644
--- a/app/[locale]/(app)/reminders/layout.tsx
+++ b/app/[locale]/(app)/checkups/layout.jsx
@@ -1,15 +1,12 @@
 // WARNING: Do NOT add `'use cache'` — requireRole() reads cookies().
 
-import type { ReactNode } from "react";
 import { requireRole } from "@/lib/auth/require-role";
 
-export default async function RemindersLayout({
-  children,
-  params,
-}: {
-  children: ReactNode;
-  params: Promise<{ locale: string }>;
-}) {
+/**
+ * @param {{ children: import("react").ReactNode, params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function CheckupsLayout({ children, params }) {
   const { locale } = await params;
   await requireRole(["admin", "receptionist", "doctor", "nurse"], locale);
   return <>{children}</>;
diff --git a/app/[locale]/(app)/dashboard/page.tsx b/app/[locale]/(app)/dashboard/page.jsx
similarity index 93%
rename from app/[locale]/(app)/dashboard/page.tsx
rename to app/[locale]/(app)/dashboard/page.jsx
index adcdf18..1eeb199 100644
--- a/app/[locale]/(app)/dashboard/page.tsx
+++ b/app/[locale]/(app)/dashboard/page.jsx
@@ -13,7 +13,11 @@ import { formatVnd, sumLineTotals } from "@/lib/billing/totals";
 
 const vnd = formatVnd;
 
-export default async function DashboardPage({ params }: { params: Promise<{ locale: string }> }) {
+/**
+ * @param {{ params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function DashboardPage({ params }) {
   await params;
 
   const t = await getTranslations("dashboard");
@@ -56,7 +60,9 @@ export default async function DashboardPage({ params }: { params: Promise<{ loca
           .gte("checkup_date", days[0])
           .lte("checkup_date", today)
           .eq("deleted", false)
-      : Promise.resolve({ data: [] as { id: number; checkup_date: string }[] }),
+      : Promise.resolve({
+          data: /** @type {{ id: number, checkup_date: string }[]} */ ([]),
+        }),
   ]);
 
   let revenue7d = days.map((d) => ({ day: d.slice(5), amount: 0 }));
@@ -74,7 +80,7 @@ export default async function DashboardPage({ params }: { params: Promise<{ loca
     ]);
     const paid = new Set((paidOrders ?? []).map((o) => o.checkup_id));
     const dateOf = new Map(weekCheckups.map((c) => [c.id, c.checkup_date]));
-    const totalByCheckup = new Map<number, number>();
+    const totalByCheckup = /** @type {Map<number, number>} */ (new Map());
     for (const r of [...(oi ?? []), ...(cs ?? [])]) {
       totalByCheckup.set(r.checkup_id, (totalByCheckup.get(r.checkup_id) ?? 0) + r.line_total);
     }
diff --git a/app/[locale]/(app)/dashboard/revenue-chart.tsx b/app/[locale]/(app)/dashboard/revenue-chart.jsx
similarity index 91%
rename from app/[locale]/(app)/dashboard/revenue-chart.tsx
rename to app/[locale]/(app)/dashboard/revenue-chart.jsx
index 3fc98a7..94ae871 100644
--- a/app/[locale]/(app)/dashboard/revenue-chart.tsx
+++ b/app/[locale]/(app)/dashboard/revenue-chart.jsx
@@ -8,7 +8,8 @@ import { formatVnd, formatVndCompact } from "@/lib/billing/totals";
 const vnd = formatVnd;
 const compact = formatVndCompact;
 
-export function RevenueChart({ data }: { data: { day: string; amount: number }[] }) {
+/** @param {{ data: { day: string, amount: number }[] }} props */
+export function RevenueChart({ data }) {
   return (
     <div className="h-56 w-full text-current">
       <ResponsiveContainer width="100%" height="100%">
diff --git a/app/[locale]/(app)/layout.tsx b/app/[locale]/(app)/layout.jsx
similarity index 89%
rename from app/[locale]/(app)/layout.tsx
rename to app/[locale]/(app)/layout.jsx
index 55b0824..736dcf7 100644
--- a/app/[locale]/(app)/layout.tsx
+++ b/app/[locale]/(app)/layout.jsx
@@ -16,19 +16,16 @@
  * "authed but unenrolled" edge case the proxy cannot detect.
  */
 
-import type { ReactNode } from "react";
 import { redirect } from "@/i18n/navigation";
 import { getServerSession } from "@/lib/auth/get-server-session";
 import { signOutAction } from "@/app/[locale]/(auth)/sign-in/actions";
 import { AppShell } from "@/components/app-shell/app-shell";
 
-export default async function AppLayout({
-  children,
-  params,
-}: {
-  children: ReactNode;
-  params: Promise<{ locale: string }>;
-}) {
+/**
+ * @param {{ children: import("react").ReactNode, params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element | null>}
+ */
+export default async function AppLayout({ children, params }) {
   const { locale } = await params;
 
   const session = await getServerSession();
diff --git a/app/[locale]/(app)/loading.tsx b/app/[locale]/(app)/loading.jsx
similarity index 85%
rename from app/[locale]/(app)/loading.tsx
rename to app/[locale]/(app)/loading.jsx
index 1da20a1..ead7e50 100644
--- a/app/[locale]/(app)/loading.tsx
+++ b/app/[locale]/(app)/loading.jsx
@@ -3,6 +3,7 @@
  * (respects prefers-reduced-motion via the global rule in globals.css).
  */
 
+/** App route-segment loading skeleton. @returns {import("react").JSX.Element} */
 export default function AppLoading() {
   return (
     <div className="flex min-h-[50vh] items-center justify-center" role="status" aria-live="polite">
diff --git a/app/[locale]/(app)/patients/[id]/edit/page.tsx b/app/[locale]/(app)/patients/[id]/edit/page.jsx
similarity index 91%
rename from app/[locale]/(app)/patients/[id]/edit/page.tsx
rename to app/[locale]/(app)/patients/[id]/edit/page.jsx
index 1c5a427..7637c11 100644
--- a/app/[locale]/(app)/patients/[id]/edit/page.tsx
+++ b/app/[locale]/(app)/patients/[id]/edit/page.jsx
@@ -6,11 +6,11 @@ import { createSupabaseServerClient } from "@/lib/supabase/server";
 import { PatientForm } from "../../patient-form";
 import { updateCustomerAction } from "../../actions";
 
-export default async function EditPatientPage({
-  params,
-}: {
-  params: Promise<{ locale: string; id: string }>;
-}) {
+/**
+ * @param {{ params: Promise<{ locale: string, id: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function EditPatientPage({ params }) {
   const { id } = await params;
   const t = await getTranslations("patients");
   const customerId = Number(id);
diff --git a/app/[locale]/(app)/patients/[id]/page.tsx b/app/[locale]/(app)/patients/[id]/page.jsx
similarity index 90%
rename from app/[locale]/(app)/patients/[id]/page.tsx
rename to app/[locale]/(app)/patients/[id]/page.jsx
index 44f0672..b1b66ad 100644
--- a/app/[locale]/(app)/patients/[id]/page.tsx
+++ b/app/[locale]/(app)/patients/[id]/page.jsx
@@ -12,17 +12,18 @@ import { Link } from "@/i18n/navigation";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
 import { Button } from "@/components/ui/button";
 
-const STATUS_STYLE: Record<string, string> = {
+/** @type {Record<string, string>} */
+const STATUS_STYLE = {
   waiting: "bg-muted text-foreground",
   in_progress: "bg-blue-100 text-blue-800 dark:bg-blue-950 dark:text-blue-200",
   done: "bg-green-100 text-green-800 dark:bg-green-950 dark:text-green-200",
 };
 
-export default async function PatientDetailPage({
-  params,
-}: {
-  params: Promise<{ locale: string; id: string }>;
-}) {
+/**
+ * @param {{ params: Promise<{ locale: string, id: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function PatientDetailPage({ params }) {
   const { locale, id } = await params;
   const t = await getTranslations("patients");
   const tCheckups = await getTranslations("checkups");
@@ -61,7 +62,7 @@ export default async function PatientDetailPage({
 
   const rows = checkups ?? [];
   const doctorIds = [
-    ...new Set(rows.map((r) => r.doctor_id).filter((d): d is number => d != null)),
+    ...new Set(rows.map((r) => r.doctor_id).filter(/** @returns {d is number} */ (d) => d != null)),
   ];
   const { data: doctors } = doctorIds.length
     ? await supabase.from("doctors").select("id, last_name, first_name").in("id", doctorIds)
@@ -91,7 +92,7 @@ export default async function PatientDetailPage({
           </p>
         </div>
         <Button asChild variant="outline">
-          <Link href={`/patients/${customer.id}/edit`} locale={locale as "vi" | "en"}>
+          <Link href={`/patients/${customer.id}/edit`} locale={/** @type {"vi" | "en"} */ (locale)}>
             {t("edit")}
           </Link>
         </Button>
@@ -106,7 +107,7 @@ export default async function PatientDetailPage({
             <li key={c.id}>
               <Link
                 href={`/checkups/${c.id}`}
-                locale={locale as "vi" | "en"}
+                locale={/** @type {"vi" | "en"} */ (locale)}
                 className="hover:bg-accent -mx-2 flex items-center justify-between gap-3 rounded-md px-2 py-3"
               >
                 <div className="min-w-0">
diff --git a/app/[locale]/(app)/patients/actions.ts b/app/[locale]/(app)/patients/actions.js
similarity index 74%
rename from app/[locale]/(app)/patients/actions.ts
rename to app/[locale]/(app)/patients/actions.js
index d505c0a..7fe1673 100644
--- a/app/[locale]/(app)/patients/actions.ts
+++ b/app/[locale]/(app)/patients/actions.js
@@ -13,19 +13,23 @@ import { revalidatePath } from "next/cache";
 import { redirect } from "@/i18n/navigation";
 import { getServerSession } from "@/lib/auth/get-server-session";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
-import type { AppRole } from "@/lib/db/roles";
-import {
-  CustomerSchema,
-  type CustomerFormState,
-  type CustomerInput,
-} from "@/lib/customers/customer-schema";
+import { CustomerSchema } from "@/lib/customers/customer-schema";
 
-const CLINICAL_ROLES: AppRole[] = ["admin", "receptionist", "doctor", "nurse"];
-const isClinical = (role: AppRole | null | undefined) => !!role && CLINICAL_ROLES.includes(role);
-const nullIfBlank = (s: string) => (s.trim().length ? s.trim() : null);
+/** @typedef {import('@/lib/db/roles').AppRole} AppRole */
+/** @typedef {import('@/lib/customers/customer-schema').CustomerFormState} CustomerFormState */
+/** @typedef {import('@/lib/customers/customer-schema').CustomerInput} CustomerInput */
 
-function readForm(formData: FormData) {
-  const get = (k: string) => String(formData.get(k) ?? "");
+/** @type {AppRole[]} */
+const CLINICAL_ROLES = ["admin", "receptionist", "doctor", "nurse"];
+/** @param {AppRole | null | undefined} role */
+const isClinical = (role) => !!role && CLINICAL_ROLES.includes(role);
+/** @param {string} s */
+const nullIfBlank = (s) => (s.trim().length ? s.trim() : null);
+
+/** @param {FormData} formData */
+function readForm(formData) {
+  /** @param {string} k */
+  const get = (k) => String(formData.get(k) ?? "");
   return {
     lastName: get("lastName"),
     firstName: get("firstName"),
@@ -39,7 +43,8 @@ function readForm(formData: FormData) {
   };
 }
 
-function toRow(d: CustomerInput) {
+/** @param {CustomerInput} d */
+function toRow(d) {
   return {
     first_name: d.firstName,
     last_name: d.lastName,
@@ -54,10 +59,12 @@ function toRow(d: CustomerInput) {
 }
 
 // ── Create (useActionState-compatible; redirects to the list on success) ─────
-export async function createCustomerAction(
-  _prev: CustomerFormState,
-  formData: FormData,
-): Promise<CustomerFormState> {
+/**
+ * @param {CustomerFormState} _prev
+ * @param {FormData} formData
+ * @returns {Promise<CustomerFormState>}
+ */
+export async function createCustomerAction(_prev, formData) {
   const t = await getTranslations("patients");
 
   const session = await getServerSession();
@@ -69,7 +76,7 @@ export async function createCustomerAction(
   if (!parsed.success) {
     return {
       status: "error",
-      fieldErrors: parsed.error.flatten().fieldErrors as Record<string, string[]>,
+      fieldErrors: /** @type {Record<string, string[]>} */ (parsed.error.flatten().fieldErrors),
       formError: null,
     };
   }
@@ -97,10 +104,12 @@ export async function createCustomerAction(
 }
 
 // ── Update ───────────────────────────────────────────────────────────────────
-export async function updateCustomerAction(
-  _prev: CustomerFormState,
-  formData: FormData,
-): Promise<CustomerFormState> {
+/**
+ * @param {CustomerFormState} _prev
+ * @param {FormData} formData
+ * @returns {Promise<CustomerFormState>}
+ */
+export async function updateCustomerAction(_prev, formData) {
   const t = await getTranslations("patients");
 
   const session = await getServerSession();
@@ -115,7 +124,7 @@ export async function updateCustomerAction(
       status: "error",
       fieldErrors: parsed.success
         ? {}
-        : (parsed.error.flatten().fieldErrors as Record<string, string[]>),
+        : /** @type {Record<string, string[]>} */ (parsed.error.flatten().fieldErrors),
       formError: parsed.success ? t("errorGeneric") : null,
     };
   }
@@ -138,7 +147,11 @@ export async function updateCustomerAction(
 }
 
 // ── Soft-delete (deactivate) ─────────────────────────────────────────────────
-export async function deactivateCustomerAction(formData: FormData): Promise<void> {
+/**
+ * @param {FormData} formData
+ * @returns {Promise<void>}
+ */
+export async function deactivateCustomerAction(formData) {
   const session = await getServerSession();
   if (!isClinical(session?.role)) return;
 
@@ -159,9 +172,11 @@ export async function deactivateCustomerAction(formData: FormData): Promise<void
 }
 
 // ── Wards for a province (cascading address dropdown) ─────────────────────────
-export async function getWardsAction(
-  provinceCode: string,
-): Promise<{ code: string; name: string }[]> {
+/**
+ * @param {string} provinceCode
+ * @returns {Promise<{ code: string, name: string }[]>}
+ */
+export async function getWardsAction(provinceCode) {
   const session = await getServerSession();
   if (!session?.role || !provinceCode) return [];
 
diff --git a/app/[locale]/(app)/patients/layout.tsx b/app/[locale]/(app)/patients/layout.jsx
similarity index 67%
rename from app/[locale]/(app)/patients/layout.tsx
rename to app/[locale]/(app)/patients/layout.jsx
index edd9e50..e25a638 100644
--- a/app/[locale]/(app)/patients/layout.tsx
+++ b/app/[locale]/(app)/patients/layout.jsx
@@ -6,16 +6,13 @@
  * /dashboard by requireRole.
  */
 
-import type { ReactNode } from "react";
 import { requireRole } from "@/lib/auth/require-role";
 
-export default async function PatientsLayout({
-  children,
-  params,
-}: {
-  children: ReactNode;
-  params: Promise<{ locale: string }>;
-}) {
+/**
+ * @param {{ children: import("react").ReactNode, params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function PatientsLayout({ children, params }) {
   const { locale } = await params;
   await requireRole(["admin", "receptionist", "doctor", "nurse"], locale);
   return <>{children}</>;
diff --git a/app/[locale]/(app)/patients/new/page.tsx b/app/[locale]/(app)/patients/new/page.jsx
similarity index 85%
rename from app/[locale]/(app)/patients/new/page.tsx
rename to app/[locale]/(app)/patients/new/page.jsx
index 1495309..58e2fc1 100644
--- a/app/[locale]/(app)/patients/new/page.tsx
+++ b/app/[locale]/(app)/patients/new/page.jsx
@@ -17,7 +17,11 @@ const BLANK = {
   addressDetail: "",
 };
 
-export default async function NewPatientPage({ params }: { params: Promise<{ locale: string }> }) {
+/**
+ * @param {{ params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function NewPatientPage({ params }) {
   await params;
   const t = await getTranslations("patients");
 
diff --git a/app/[locale]/(app)/patients/page.tsx b/app/[locale]/(app)/patients/page.jsx
similarity index 81%
rename from app/[locale]/(app)/patients/page.tsx
rename to app/[locale]/(app)/patients/page.jsx
index d44af9a..362ad35 100644
--- a/app/[locale]/(app)/patients/page.tsx
+++ b/app/[locale]/(app)/patients/page.jsx
@@ -13,27 +13,22 @@ import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { deactivateCustomerAction } from "./actions";
 
-export default async function PatientsPage({
-  params,
-  searchParams,
-}: {
-  params: Promise<{ locale: string }>;
-  searchParams: Promise<{ q?: string }>;
-}) {
+/**
+ * @typedef {{ id: number, first_name: string, last_name: string, phone: string | null, dob: string | null }} PatientRow
+ */
+
+/**
+ * @param {{ params: Promise<{ locale: string }>, searchParams: Promise<{ q?: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function PatientsPage({ params, searchParams }) {
   const { locale } = await params;
   const { q = "" } = await searchParams;
   const t = await getTranslations("patients");
 
   const supabase = await createSupabaseServerClient();
   const { data } = await supabase.rpc("search_customers", { q });
-  type PatientRow = {
-    id: number;
-    first_name: string;
-    last_name: string;
-    phone: string | null;
-    dob: string | null;
-  };
-  const patients = (data ?? []) as PatientRow[];
+  const patients = /** @type {PatientRow[]} */ (data ?? []);
 
   // Recently seen: most recent distinct customers by their latest checkup.
   const { data: recentCheckups } = await supabase
@@ -44,8 +39,10 @@ export default async function PatientsPage({
     .order("id", { ascending: false })
     .limit(50);
 
-  const seenIds = new Set<number>();
-  const recentIds: number[] = [];
+  /** @type {Set<number>} */
+  const seenIds = new Set();
+  /** @type {number[]} */
+  const recentIds = [];
   for (const row of recentCheckups ?? []) {
     if (!seenIds.has(row.customer_id)) {
       seenIds.add(row.customer_id);
@@ -67,14 +64,14 @@ export default async function PatientsPage({
   );
   const recentlySeen = recentIds
     .filter((cid) => recentNames.has(cid))
-    .map((cid) => ({ id: cid, name: recentNames.get(cid)! }));
+    .map((cid) => ({ id: cid, name: /** @type {string} */ (recentNames.get(cid)) }));
 
   return (
     <div className="mx-auto max-w-3xl px-4 py-10">
       <div className="mb-6 flex items-center justify-between gap-4">
         <h1 className="text-foreground text-xl font-semibold">{t("title")}</h1>
         <Button asChild size="lg">
-          <Link href="/patients/new" locale={locale as "vi" | "en"}>
+          <Link href="/patients/new" locale={/** @type {"vi" | "en"} */ (locale)}>
             {t("new")}
           </Link>
         </Button>
@@ -90,7 +87,7 @@ export default async function PatientsPage({
               <Link
                 key={p.id}
                 href={`/patients/${p.id}`}
-                locale={locale as "vi" | "en"}
+                locale={/** @type {"vi" | "en"} */ (locale)}
                 className="border-border bg-muted/50 hover:bg-accent rounded-full border px-3 py-1 text-sm"
               >
                 {p.name}
@@ -121,7 +118,7 @@ export default async function PatientsPage({
               <div className="min-w-0">
                 <Link
                   href={`/patients/${p.id}`}
-                  locale={locale as "vi" | "en"}
+                  locale={/** @type {"vi" | "en"} */ (locale)}
                   className="text-foreground block truncate font-medium hover:underline"
                 >
                   {p.last_name} {p.first_name}
@@ -132,7 +129,10 @@ export default async function PatientsPage({
               </div>
               <div className="flex shrink-0 items-center gap-1">
                 <Button asChild variant="outline">
-                  <Link href={`/patients/${p.id}/edit`} locale={locale as "vi" | "en"}>
+                  <Link
+                    href={`/patients/${p.id}/edit`}
+                    locale={/** @type {"vi" | "en"} */ (locale)}
+                  >
                     {t("edit")}
                   </Link>
                 </Button>
diff --git a/app/[locale]/(app)/patients/patient-form.tsx b/app/[locale]/(app)/patients/patient-form.jsx
similarity index 84%
rename from app/[locale]/(app)/patients/patient-form.tsx
rename to app/[locale]/(app)/patients/patient-form.jsx
index 9ae2e07..5bea0b6 100644
--- a/app/[locale]/(app)/patients/patient-form.tsx
+++ b/app/[locale]/(app)/patients/patient-form.jsx
@@ -14,50 +14,50 @@ import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
 import { getWardsAction } from "./actions";
-import type { CustomerFormState } from "@/lib/customers/customer-schema";
 
-type Option = { code: string; name: string };
+/** @typedef {import('@/lib/customers/customer-schema').CustomerFormState} CustomerFormState */
 
-export type PatientDefaults = {
-  id?: number;
-  lastName: string;
-  firstName: string;
-  dob: string;
-  gender: string;
-  phone: string;
-  cccd: string;
-  provinceCode: string;
-  wardCode: string;
-  addressDetail: string;
-};
+/** @typedef {{ code: string, name: string }} Option */
+
+/**
+ * @typedef {object} PatientDefaults
+ * @property {number} [id]
+ * @property {string} lastName
+ * @property {string} firstName
+ * @property {string} dob
+ * @property {string} gender
+ * @property {string} phone
+ * @property {string} cccd
+ * @property {string} provinceCode
+ * @property {string} wardCode
+ * @property {string} addressDetail
+ */
 
 const SELECT_CLASS =
   "border-input bg-background text-foreground focus-visible:ring-ring h-10 w-full rounded-md border px-3 text-sm focus:outline-none focus-visible:ring-2 disabled:opacity-50";
 
-export function PatientForm({
-  mode,
-  action,
-  provinces,
-  initialWards,
-  defaults,
-}: {
-  mode: "create" | "edit";
-  action: (prev: CustomerFormState, formData: FormData) => Promise<CustomerFormState>;
-  provinces: Option[];
-  initialWards: Option[];
-  defaults: PatientDefaults;
-}) {
+/**
+ * @param {{
+ *   mode: "create" | "edit",
+ *   action: (prev: CustomerFormState, formData: FormData) => Promise<CustomerFormState>,
+ *   provinces: Option[],
+ *   initialWards: Option[],
+ *   defaults: PatientDefaults,
+ * }} props
+ */
+export function PatientForm({ mode, action, provinces, initialWards, defaults }) {
   const t = useTranslations("patients");
-  const [state, dispatch, isPending] = useActionState<CustomerFormState, FormData>(action, {
+  const [state, dispatch, isPending] = useActionState(action, {
     status: "idle",
   });
 
   const [province, setProvince] = useState(defaults.provinceCode);
   const [ward, setWard] = useState(defaults.wardCode);
-  const [wards, setWards] = useState<Option[]>(initialWards);
+  const [wards, setWards] = useState(/** @type {Option[]} */ (initialWards));
   const [loadingWards, startWards] = useTransition();
 
-  function onProvinceChange(code: string) {
+  /** @param {string} code */
+  function onProvinceChange(code) {
     setProvince(code);
     setWard("");
     startWards(async () => setWards(await getWardsAction(code)));
@@ -66,7 +66,8 @@ export function PatientForm({
   const fe = state.status === "error" ? state.fieldErrors : {};
   const formError = state.status === "error" ? state.formError : null;
 
-  const err = (field: string) =>
+  /** @param {string} field */
+  const err = (field) =>
     fe[field]?.length ? (
       <p className="text-destructive text-sm" role="alert">
         {fe[field][0]}
diff --git a/app/[locale]/(app)/queue/actions.ts b/app/[locale]/(app)/queue/actions.js
similarity index 77%
rename from app/[locale]/(app)/queue/actions.ts
rename to app/[locale]/(app)/queue/actions.js
index 7db25da..418b70e 100644
--- a/app/[locale]/(app)/queue/actions.ts
+++ b/app/[locale]/(app)/queue/actions.js
@@ -13,24 +13,28 @@ import { revalidatePath } from "next/cache";
 import { redirect } from "@/i18n/navigation";
 import { getServerSession } from "@/lib/auth/get-server-session";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
-import type { AppRole } from "@/lib/db/roles";
-import {
-  RegisterCheckupSchema,
-  SetQueueCounterSchema,
-  type RegisterCheckupState,
-  type SetQueueCounterState,
-} from "@/lib/checkups/checkup-schema";
+import { RegisterCheckupSchema, SetQueueCounterSchema } from "@/lib/checkups/checkup-schema";
 
-const CLINICAL: AppRole[] = ["admin", "receptionist", "doctor", "nurse"];
-const isClinical = (r: AppRole | null | undefined) => !!r && CLINICAL.includes(r);
+/** @typedef {import('@/lib/db/roles').AppRole} AppRole */
+/** @typedef {import('@/lib/checkups/checkup-schema').RegisterCheckupState} RegisterCheckupState */
+/** @typedef {import('@/lib/checkups/checkup-schema').SetQueueCounterState} SetQueueCounterState */
 
-const COUNTER_MANAGERS: AppRole[] = ["admin", "receptionist"];
-const canManageCounter = (r: AppRole | null | undefined) => !!r && COUNTER_MANAGERS.includes(r);
+/** @type {AppRole[]} */
+const CLINICAL = ["admin", "receptionist", "doctor", "nurse"];
+/** @param {AppRole | null | undefined} r */
+const isClinical = (r) => !!r && CLINICAL.includes(r);
 
-export async function registerCheckupAction(
-  _prev: RegisterCheckupState,
-  formData: FormData,
-): Promise<RegisterCheckupState> {
+/** @type {AppRole[]} */
+const COUNTER_MANAGERS = ["admin", "receptionist"];
+/** @param {AppRole | null | undefined} r */
+const canManageCounter = (r) => !!r && COUNTER_MANAGERS.includes(r);
+
+/**
+ * @param {RegisterCheckupState} _prev
+ * @param {FormData} formData
+ * @returns {Promise<RegisterCheckupState>}
+ */
+export async function registerCheckupAction(_prev, formData) {
   const t = await getTranslations("queue");
 
   const session = await getServerSession();
@@ -47,7 +51,7 @@ export async function registerCheckupAction(
   if (!parsed.success) {
     return {
       status: "error",
-      fieldErrors: parsed.error.flatten().fieldErrors as Record<string, string[]>,
+      fieldErrors: /** @type {Record<string, string[]>} */ (parsed.error.flatten().fieldErrors),
       formError: null,
     };
   }
@@ -87,10 +91,12 @@ export async function registerCheckupAction(
  * resetting after a printer jam, etc). admin/receptionist only — RLS +
  * set_queue_counter's role check enforce it; this is defense-in-depth.
  */
-export async function setQueueCounterAction(
-  _prev: SetQueueCounterState,
-  formData: FormData,
-): Promise<SetQueueCounterState> {
+/**
+ * @param {SetQueueCounterState} _prev
+ * @param {FormData} formData
+ * @returns {Promise<SetQueueCounterState>}
+ */
+export async function setQueueCounterAction(_prev, formData) {
   const t = await getTranslations("queue");
 
   const session = await getServerSession();
@@ -135,7 +141,11 @@ export async function setQueueCounterAction(
  * and marks it in_progress. On success, redirects straight to the checkup
  * screen so the doctor never has to find the row in the list themselves.
  */
-export async function callNextPatientAction(formData: FormData): Promise<void> {
+/**
+ * @param {FormData} formData
+ * @returns {Promise<void>}
+ */
+export async function callNextPatientAction(formData) {
   const session = await getServerSession();
   if (!isClinical(session?.role)) return;
 
@@ -161,7 +171,11 @@ export async function callNextPatientAction(formData: FormData): Promise<void> {
   }
 }
 
-export async function callPatientAction(formData: FormData): Promise<void> {
+/**
+ * @param {FormData} formData
+ * @returns {Promise<void>}
+ */
+export async function callPatientAction(formData) {
   const session = await getServerSession();
   if (!isClinical(session?.role)) return;
 
diff --git a/app/[locale]/(app)/queue/call-next-button.tsx b/app/[locale]/(app)/queue/call-next-button.jsx
similarity index 80%
rename from app/[locale]/(app)/queue/call-next-button.tsx
rename to app/[locale]/(app)/queue/call-next-button.jsx
index 2dbda9b..a2f0e8b 100644
--- a/app/[locale]/(app)/queue/call-next-button.tsx
+++ b/app/[locale]/(app)/queue/call-next-button.jsx
@@ -16,28 +16,22 @@ import { callNextPatientAction } from "./actions";
 
 const TYPING_TAGS = new Set(["INPUT", "TEXTAREA", "SELECT"]);
 
-export function CallNextButton({
-  shiftId,
-  shiftLabel,
-  waitingCount,
-  enableShortcut,
-}: {
-  shiftId: number;
-  shiftLabel: string;
-  waitingCount: number;
-  enableShortcut: boolean;
-}) {
+/**
+ * @param {{ shiftId: number, shiftLabel: string, waitingCount: number, enableShortcut: boolean }} props
+ */
+export function CallNextButton({ shiftId, shiftLabel, waitingCount, enableShortcut }) {
   const t = useTranslations("queue");
-  const formRef = useRef<HTMLFormElement>(null);
+  const formRef = useRef(/** @type {HTMLFormElement | null} */ (null));
 
   useEffect(() => {
     if (!enableShortcut) return;
 
-    function onKeyDown(event: KeyboardEvent) {
+    /** @param {KeyboardEvent} event */
+    function onKeyDown(event) {
       if (!event.altKey || event.ctrlKey || event.metaKey || event.shiftKey) return;
       if (event.key.toLowerCase() !== "n") return;
 
-      const target = event.target as HTMLElement | null;
+      const target = /** @type {HTMLElement | null} */ (event.target);
       if (target && (TYPING_TAGS.has(target.tagName) || target.isContentEditable)) return;
 
       event.preventDefault();
diff --git a/app/[locale]/(app)/queue/counter-form.tsx b/app/[locale]/(app)/queue/counter-form.jsx
similarity index 80%
rename from app/[locale]/(app)/queue/counter-form.tsx
rename to app/[locale]/(app)/queue/counter-form.jsx
index 9562e4b..6abf383 100644
--- a/app/[locale]/(app)/queue/counter-form.tsx
+++ b/app/[locale]/(app)/queue/counter-form.jsx
@@ -11,15 +11,16 @@ import { useTranslations } from "next-intl";
 
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
-import type { SetQueueCounterState } from "@/lib/checkups/checkup-schema";
 import { setQueueCounterAction } from "./actions";
 
-export function CounterForm({ shiftId, currentValue }: { shiftId: number; currentValue: number }) {
+/** @typedef {import('@/lib/checkups/checkup-schema').SetQueueCounterState} SetQueueCounterState */
+
+/**
+ * @param {{ shiftId: number, currentValue: number }} props
+ */
+export function CounterForm({ shiftId, currentValue }) {
   const t = useTranslations("queue");
-  const [state, dispatch, isPending] = useActionState<SetQueueCounterState, FormData>(
-    setQueueCounterAction,
-    { status: "idle" },
-  );
+  const [state, dispatch, isPending] = useActionState(setQueueCounterAction, { status: "idle" });
 
   return (
     <form action={dispatch} className="flex items-center gap-2">
diff --git a/app/[locale]/(app)/queue/layout.tsx b/app/[locale]/(app)/queue/layout.jsx
similarity index 54%
rename from app/[locale]/(app)/queue/layout.tsx
rename to app/[locale]/(app)/queue/layout.jsx
index 5ccb663..7949c57 100644
--- a/app/[locale]/(app)/queue/layout.tsx
+++ b/app/[locale]/(app)/queue/layout.jsx
@@ -1,15 +1,12 @@
 // WARNING: Do NOT add `'use cache'` — requireRole() reads cookies().
 
-import type { ReactNode } from "react";
 import { requireRole } from "@/lib/auth/require-role";
 
-export default async function QueueLayout({
-  children,
-  params,
-}: {
-  children: ReactNode;
-  params: Promise<{ locale: string }>;
-}) {
+/**
+ * @param {{ children: import("react").ReactNode, params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function QueueLayout({ children, params }) {
   const { locale } = await params;
   await requireRole(["admin", "receptionist", "doctor", "nurse"], locale);
   return <>{children}</>;
diff --git a/app/[locale]/(app)/queue/page.tsx b/app/[locale]/(app)/queue/page.jsx
similarity index 92%
rename from app/[locale]/(app)/queue/page.tsx
rename to app/[locale]/(app)/queue/page.jsx
index 00640c3..0a05389 100644
--- a/app/[locale]/(app)/queue/page.tsx
+++ b/app/[locale]/(app)/queue/page.jsx
@@ -18,13 +18,18 @@ import { callPatientAction } from "./actions";
 
 const COUNTER_MANAGERS = new Set(["admin", "receptionist"]);
 
-const STATUS_STYLE: Record<string, string> = {
+/** @type {Record<string, string>} */
+const STATUS_STYLE = {
   waiting: "bg-muted text-foreground",
   in_progress: "bg-blue-100 text-blue-800 dark:bg-blue-950 dark:text-blue-200",
   done: "bg-green-100 text-green-800 dark:bg-green-950 dark:text-green-200",
 };
 
-export default async function QueuePage({ params }: { params: Promise<{ locale: string }> }) {
+/**
+ * @param {{ params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function QueuePage({ params }) {
   const { locale } = await params;
   const t = await getTranslations("queue");
   const tShift = await getTranslations("shifts");
@@ -71,7 +76,8 @@ export default async function QueuePage({ params }: { params: Promise<{ locale:
   const shiftCode = new Map((shifts ?? []).map((s) => [s.id, s.code]));
   const counterByShift = new Map((counters ?? []).map((c) => [c.shift_id, c.last_number]));
 
-  const waitingCountByShift = new Map<number, number>();
+  /** @type {Map<number, number>} */
+  const waitingCountByShift = new Map();
   for (const r of rows) {
     if (r.status === "waiting" && r.shift_id != null) {
       waitingCountByShift.set(r.shift_id, (waitingCountByShift.get(r.shift_id) ?? 0) + 1);
@@ -128,7 +134,8 @@ export default async function QueuePage({ params }: { params: Promise<{ locale:
         <h2 className="text-foreground mb-3 text-sm font-medium">{t("registerTitle")}</h2>
         <RegisterForm
           patients={(patients ?? []).map(
-            (p: { id: number; last_name: string; first_name: string }) => ({
+            /** @param {{ id: number, last_name: string, first_name: string }} p */
+            (p) => ({
               id: p.id,
               last_name: p.last_name,
               first_name: p.first_name,
@@ -158,7 +165,7 @@ export default async function QueuePage({ params }: { params: Promise<{ locale:
                   </p>
                   <p className="text-muted-foreground truncate text-xs">
                     {shiftCode.get(c.shift_id ?? -1)
-                      ? tShift(shiftCode.get(c.shift_id ?? -1)!)
+                      ? tShift(/** @type {string} */ (shiftCode.get(c.shift_id ?? -1)))
                       : "—"}
                     {c.doctor_id ? ` · ${docName.get(c.doctor_id) ?? "—"}` : ""}
                   </p>
@@ -179,7 +186,7 @@ export default async function QueuePage({ params }: { params: Promise<{ locale:
                   </form>
                 )}
                 <Button asChild variant="outline">
-                  <Link href={`/checkups/${c.id}`} locale={locale as "vi" | "en"}>
+                  <Link href={`/checkups/${c.id}`} locale={/** @type {"vi" | "en"} */ (locale)}>
                     {t("open")}
                   </Link>
                 </Button>
diff --git a/app/[locale]/(app)/queue/queue-realtime.tsx b/app/[locale]/(app)/queue/queue-realtime.jsx
similarity index 86%
rename from app/[locale]/(app)/queue/queue-realtime.tsx
rename to app/[locale]/(app)/queue/queue-realtime.jsx
index e1ec69a..e3f7895 100644
--- a/app/[locale]/(app)/queue/queue-realtime.tsx
+++ b/app/[locale]/(app)/queue/queue-realtime.jsx
@@ -20,7 +20,7 @@ import { useTranslations } from "next-intl";
 import { Wifi, WifiOff } from "lucide-react";
 import { createSupabaseBrowserClient } from "@/lib/supabase/client";
 
-type ConnectionStatus = "live" | "disconnected";
+/** @typedef {"live" | "disconnected"} ConnectionStatus */
 
 const timeFormatter = new Intl.DateTimeFormat("vi-VN", {
   hour: "2-digit",
@@ -29,11 +29,12 @@ const timeFormatter = new Intl.DateTimeFormat("vi-VN", {
   hour12: false,
 });
 
+/** Realtime connection badge: subscribes to queue changes and refreshes the route on updates. @returns {import("react").JSX.Element} */
 export function QueueRealtime() {
   const router = useRouter();
   const t = useTranslations("queue");
-  const [status, setStatus] = useState<ConnectionStatus>("disconnected");
-  const [lastUpdatedAt, setLastUpdatedAt] = useState<string | null>(null);
+  const [status, setStatus] = useState(/** @type {ConnectionStatus} */ ("disconnected"));
+  const [lastUpdatedAt, setLastUpdatedAt] = useState(/** @type {string | null} */ (null));
 
   useEffect(() => {
     const supabase = createSupabaseBrowserClient();
diff --git a/app/[locale]/(app)/queue/register-form.tsx b/app/[locale]/(app)/queue/register-form.jsx
similarity index 84%
rename from app/[locale]/(app)/queue/register-form.tsx
rename to app/[locale]/(app)/queue/register-form.jsx
index e3b8ac6..27930fa 100644
--- a/app/[locale]/(app)/queue/register-form.tsx
+++ b/app/[locale]/(app)/queue/register-form.jsx
@@ -12,33 +12,26 @@ import { useTranslations } from "next-intl";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
-import type { RegisterCheckupState } from "@/lib/checkups/checkup-schema";
 import { registerCheckupAction } from "./actions";
 
-type Patient = { id: number; last_name: string; first_name: string };
-type Shift = { id: number; code: string };
-type Doctor = { id: number; last_name: string; first_name: string };
+/** @typedef {import('@/lib/checkups/checkup-schema').RegisterCheckupState} RegisterCheckupState */
+
+/** @typedef {{ id: number, last_name: string, first_name: string }} Patient */
+/** @typedef {{ id: number, code: string }} Shift */
+/** @typedef {{ id: number, last_name: string, first_name: string }} Doctor */
 
 const SELECT =
   "border-input bg-background text-foreground focus-visible:ring-ring h-10 w-full rounded-md border px-3 text-sm focus:outline-none focus-visible:ring-2 disabled:opacity-50";
 
-export function RegisterForm({
-  patients,
-  shifts,
-  doctors,
-}: {
-  patients: Patient[];
-  shifts: Shift[];
-  doctors: Doctor[];
-}) {
+/**
+ * @param {{ patients: Patient[], shifts: Shift[], doctors: Doctor[] }} props
+ */
+export function RegisterForm({ patients, shifts, doctors }) {
   const t = useTranslations("queue");
   const tShift = useTranslations("shifts");
-  const formRef = useRef<HTMLFormElement>(null);
+  const formRef = useRef(/** @type {HTMLFormElement | null} */ (null));
 
-  const [state, dispatch, isPending] = useActionState<RegisterCheckupState, FormData>(
-    registerCheckupAction,
-    { status: "idle" },
-  );
+  const [state, dispatch, isPending] = useActionState(registerCheckupAction, { status: "idle" });
 
   useEffect(() => {
     if (state.status === "success") formRef.current?.reset();
diff --git a/app/[locale]/(app)/checkups/layout.tsx b/app/[locale]/(app)/reminders/layout.jsx
similarity index 54%
rename from app/[locale]/(app)/checkups/layout.tsx
rename to app/[locale]/(app)/reminders/layout.jsx
index de55f53..f7d5645 100644
--- a/app/[locale]/(app)/checkups/layout.tsx
+++ b/app/[locale]/(app)/reminders/layout.jsx
@@ -1,15 +1,12 @@
 // WARNING: Do NOT add `'use cache'` — requireRole() reads cookies().
 
-import type { ReactNode } from "react";
 import { requireRole } from "@/lib/auth/require-role";
 
-export default async function CheckupsLayout({
-  children,
-  params,
-}: {
-  children: ReactNode;
-  params: Promise<{ locale: string }>;
-}) {
+/**
+ * @param {{ children: import("react").ReactNode, params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function RemindersLayout({ children, params }) {
   const { locale } = await params;
   await requireRole(["admin", "receptionist", "doctor", "nurse"], locale);
   return <>{children}</>;
diff --git a/app/[locale]/(app)/reminders/page.tsx b/app/[locale]/(app)/reminders/page.jsx
similarity index 94%
rename from app/[locale]/(app)/reminders/page.tsx
rename to app/[locale]/(app)/reminders/page.jsx
index c1d9573..8696e3d 100644
--- a/app/[locale]/(app)/reminders/page.tsx
+++ b/app/[locale]/(app)/reminders/page.jsx
@@ -8,7 +8,11 @@
 import { getTranslations } from "next-intl/server";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
 
-export default async function RemindersPage({ params }: { params: Promise<{ locale: string }> }) {
+/**
+ * @param {{ params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function RemindersPage({ params }) {
   await params;
   const t = await getTranslations("reminders");
 
diff --git a/app/[locale]/(app)/reports/catalog/route.ts b/app/[locale]/(app)/reports/catalog/route.js
similarity index 93%
rename from app/[locale]/(app)/reports/catalog/route.ts
rename to app/[locale]/(app)/reports/catalog/route.js
index 64fece1..6992dc9 100644
--- a/app/[locale]/(app)/reports/catalog/route.ts
+++ b/app/[locale]/(app)/reports/catalog/route.js
@@ -13,6 +13,7 @@ import { createSupabaseServerClient } from "@/lib/supabase/server";
 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
 
+/** Streams the catalog report as an XLSX download. @returns {Promise<Response>} */
 export async function GET() {
   const session = await getServerSession();
   if (session?.role !== "admin" && session?.role !== "cashier") {
@@ -53,7 +54,7 @@ export async function GET() {
   const wb = XLSX.utils.book_new();
   XLSX.utils.book_append_sheet(wb, XLSX.utils.json_to_sheet(medicineRows), t("medicinesSheet"));
   XLSX.utils.book_append_sheet(wb, XLSX.utils.json_to_sheet(serviceRows), t("servicesSheet"));
-  const buffer: Buffer = XLSX.write(wb, { type: "buffer", bookType: "xlsx" });
+  const buffer = /** @type {Buffer} */ (XLSX.write(wb, { type: "buffer", bookType: "xlsx" }));
 
   const today = new Intl.DateTimeFormat("en-CA", { timeZone: "Asia/Ho_Chi_Minh" }).format(
     new Date(),
diff --git a/app/[locale]/(app)/reports/patients/route.ts b/app/[locale]/(app)/reports/patients/route.js
similarity index 81%
rename from app/[locale]/(app)/reports/patients/route.ts
rename to app/[locale]/(app)/reports/patients/route.js
index 69b8208..03fe3d6 100644
--- a/app/[locale]/(app)/reports/patients/route.ts
+++ b/app/[locale]/(app)/reports/patients/route.js
@@ -13,6 +13,7 @@ import { createSupabaseServerClient } from "@/lib/supabase/server";
 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
 
+/** Streams the patients report as an XLSX download. @returns {Promise<Response>} */
 export async function GET() {
   const session = await getServerSession();
   if (session?.role !== "admin" && session?.role !== "cashier") {
@@ -32,21 +33,21 @@ export async function GET() {
     .order("last_name", { ascending: true })
     .order("first_name", { ascending: true });
 
+  /** @param {string | null} v
+   *  @returns {v is string} */
+  const isString = (v) => v != null;
+
   const rows = customers ?? [];
-  const provinceCodes = [
-    ...new Set(rows.map((r) => r.province_code).filter((v): v is string => v != null)),
-  ];
-  const wardCodes = [
-    ...new Set(rows.map((r) => r.ward_code).filter((v): v is string => v != null)),
-  ];
+  const provinceCodes = [...new Set(rows.map((r) => r.province_code).filter(isString))];
+  const wardCodes = [...new Set(rows.map((r) => r.ward_code).filter(isString))];
 
   const [{ data: provinces }, { data: wards }] = await Promise.all([
     provinceCodes.length
       ? supabase.from("provinces").select("code, name").in("code", provinceCodes)
-      : Promise.resolve({ data: [] as { code: string; name: string }[] }),
+      : Promise.resolve({ data: /** @type {{ code: string, name: string }[]} */ ([]) }),
     wardCodes.length
       ? supabase.from("wards").select("code, name").in("code", wardCodes)
-      : Promise.resolve({ data: [] as { code: string; name: string }[] }),
+      : Promise.resolve({ data: /** @type {{ code: string, name: string }[]} */ ([]) }),
   ]);
 
   const provinceName = new Map((provinces ?? []).map((p) => [p.code, p.name]));
@@ -71,7 +72,7 @@ export async function GET() {
   const ws = XLSX.utils.json_to_sheet(sheetRows);
   const wb = XLSX.utils.book_new();
   XLSX.utils.book_append_sheet(wb, ws, "Patients");
-  const buffer: Buffer = XLSX.write(wb, { type: "buffer", bookType: "xlsx" });
+  const buffer = /** @type {Buffer} */ (XLSX.write(wb, { type: "buffer", bookType: "xlsx" }));
 
   const today = new Intl.DateTimeFormat("en-CA", { timeZone: "Asia/Ho_Chi_Minh" }).format(
     new Date(),
diff --git a/app/[locale]/(app)/reports/revenue/route.ts b/app/[locale]/(app)/reports/revenue/route.js
similarity index 78%
rename from app/[locale]/(app)/reports/revenue/route.ts
rename to app/[locale]/(app)/reports/revenue/route.js
index 03def4c..80a4adc 100644
--- a/app/[locale]/(app)/reports/revenue/route.ts
+++ b/app/[locale]/(app)/reports/revenue/route.js
@@ -16,7 +16,11 @@ export const dynamic = "force-dynamic";
 
 const MONTH_RE = /^\d{4}-\d{2}$/;
 
-function monthRange(month: string): { start: string; end: string } {
+/**
+ * @param {string} month
+ * @returns {{ start: string, end: string }}
+ */
+function monthRange(month) {
   const parts = month.split("-");
   const y = Number(parts[0] ?? 0);
   const m = Number(parts[1] ?? 1);
@@ -27,7 +31,8 @@ function monthRange(month: string): { start: string; end: string } {
   return { start, end };
 }
 
-export async function GET(req: Request) {
+/** @param {Request} req */
+export async function GET(req) {
   const session = await getServerSession();
   if (session?.role !== "admin" && session?.role !== "cashier") {
     return new Response("Forbidden", { status: 403 });
@@ -69,7 +74,7 @@ export async function GET(req: Request) {
         .in("checkup_id", ids)
         .eq("payment_status", "paid")
     : {
-        data: [] as { checkup_id: number; payment_status: string; payment_method: string | null }[],
+        data: /** @type {{ checkup_id: number, payment_status: string, payment_method: string | null }[]} */ ([]),
       };
 
   const paidIds = new Set((orders ?? []).map((o) => o.checkup_id));
@@ -81,43 +86,51 @@ export async function GET(req: Request) {
   const [{ data: custs }, { data: items }, { data: svcs }] = await Promise.all([
     custIds.length
       ? supabase.from("customers").select("id, last_name, first_name").in("id", custIds)
-      : Promise.resolve({ data: [] as { id: number; last_name: string; first_name: string }[] }),
+      : Promise.resolve({
+          data: /** @type {{ id: number, last_name: string, first_name: string }[]} */ ([]),
+        }),
     paidCheckupIds.length
       ? supabase
           .from("order_items")
           .select("checkup_id, line_total")
           .in("checkup_id", paidCheckupIds)
-      : Promise.resolve({ data: [] as { checkup_id: number; line_total: number }[] }),
+      : Promise.resolve({
+          data: /** @type {{ checkup_id: number, line_total: number }[]} */ ([]),
+        }),
     paidCheckupIds.length
       ? supabase
           .from("checkup_services")
           .select("checkup_id, line_total")
           .in("checkup_id", paidCheckupIds)
-      : Promise.resolve({ data: [] as { checkup_id: number; line_total: number }[] }),
+      : Promise.resolve({
+          data: /** @type {{ checkup_id: number, line_total: number }[]} */ ([]),
+        }),
   ]);
 
   const name = new Map((custs ?? []).map((c) => [c.id, `${c.last_name} ${c.first_name}`]));
-  const medSubtotalBy = new Map<number, number>();
+  const medSubtotalBy = /** @type {Map<number, number>} */ (new Map());
   for (const it of items ?? []) {
     medSubtotalBy.set(it.checkup_id, (medSubtotalBy.get(it.checkup_id) ?? 0) + it.line_total);
   }
-  const svcSubtotalBy = new Map<number, number>();
+  const svcSubtotalBy = /** @type {Map<number, number>} */ (new Map());
   for (const sv of svcs ?? []) {
     svcSubtotalBy.set(sv.checkup_id, (svcSubtotalBy.get(sv.checkup_id) ?? 0) + sv.line_total);
   }
 
-  const KNOWN_METHODS = ["cash", "card", "transfer"] as const;
-  const methodLabel = (method: string | null) => {
+  const KNOWN_METHODS = /** @type {const} */ (["cash", "card", "transfer"]);
+  /** @param {string | null} method */
+  const methodLabel = (method) => {
     if (!method) return "";
-    return (KNOWN_METHODS as readonly string[]).includes(method)
+    return /** @type {readonly string[]} */ (KNOWN_METHODS).includes(method)
       ? tBilling(`method.${method}`)
       : method;
   };
 
-  type RevenueRow = Record<string, string | number>;
+  /** @typedef {Record<string, string | number>} RevenueRow */
 
   let grandTotal = 0;
-  const sheetRows: RevenueRow[] = paidRows.map((r) => {
+  /** @type {RevenueRow[]} */
+  const sheetRows = paidRows.map((r) => {
     const medSubtotal = medSubtotalBy.get(r.id) ?? 0;
     const svcSubtotal = svcSubtotalBy.get(r.id) ?? 0;
     const total = medSubtotal + svcSubtotal;
@@ -144,7 +157,7 @@ export async function GET(req: Request) {
   const ws = XLSX.utils.json_to_sheet(sheetRows);
   const wb = XLSX.utils.book_new();
   XLSX.utils.book_append_sheet(wb, ws, "Revenue");
-  const buffer: Buffer = XLSX.write(wb, { type: "buffer", bookType: "xlsx" });
+  const buffer = /** @type {Buffer} */ (XLSX.write(wb, { type: "buffer", bookType: "xlsx" }));
 
   return new Response(new Uint8Array(buffer), {
     headers: {
diff --git a/app/[locale]/(app)/reports/visits/route.ts b/app/[locale]/(app)/reports/visits/route.js
similarity index 80%
rename from app/[locale]/(app)/reports/visits/route.ts
rename to app/[locale]/(app)/reports/visits/route.js
index a2c4970..c2dc487 100644
--- a/app/[locale]/(app)/reports/visits/route.ts
+++ b/app/[locale]/(app)/reports/visits/route.js
@@ -14,7 +14,11 @@ export const dynamic = "force-dynamic";
 
 const MONTH_RE = /^\d{4}-\d{2}$/;
 
-function monthRange(month: string): { start: string; end: string } {
+/**
+ * @param {string} month
+ * @returns {{ start: string, end: string }}
+ */
+function monthRange(month) {
   const parts = month.split("-");
   const y = Number(parts[0] ?? 0);
   const m = Number(parts[1] ?? 1);
@@ -25,7 +29,8 @@ function monthRange(month: string): { start: string; end: string } {
   return { start, end };
 }
 
-export async function GET(req: Request) {
+/** @param {Request} req */
+export async function GET(req) {
   const session = await getServerSession();
   if (session?.role !== "admin" && session?.role !== "cashier") {
     return new Response("Forbidden", { status: 403 });
@@ -63,20 +68,28 @@ export async function GET(req: Request) {
   const [{ data: custs }, { data: items }, { data: svcs }, { data: orders }] = await Promise.all([
     custIds.length
       ? supabase.from("customers").select("id, last_name, first_name").in("id", custIds)
-      : Promise.resolve({ data: [] as { id: number; last_name: string; first_name: string }[] }),
+      : Promise.resolve({
+          data: /** @type {{ id: number, last_name: string, first_name: string }[]} */ ([]),
+        }),
     ids.length
       ? supabase.from("order_items").select("checkup_id, line_total").in("checkup_id", ids)
-      : Promise.resolve({ data: [] as { checkup_id: number; line_total: number }[] }),
+      : Promise.resolve({
+          data: /** @type {{ checkup_id: number, line_total: number }[]} */ ([]),
+        }),
     ids.length
       ? supabase.from("checkup_services").select("checkup_id, line_total").in("checkup_id", ids)
-      : Promise.resolve({ data: [] as { checkup_id: number; line_total: number }[] }),
+      : Promise.resolve({
+          data: /** @type {{ checkup_id: number, line_total: number }[]} */ ([]),
+        }),
     ids.length
       ? supabase.from("medicine_orders").select("checkup_id, payment_status").in("checkup_id", ids)
-      : Promise.resolve({ data: [] as { checkup_id: number; payment_status: string }[] }),
+      : Promise.resolve({
+          data: /** @type {{ checkup_id: number, payment_status: string }[]} */ ([]),
+        }),
   ]);
 
   const name = new Map((custs ?? []).map((c) => [c.id, `${c.last_name} ${c.first_name}`]));
-  const totalBy = new Map<number, number>();
+  const totalBy = /** @type {Map<number, number>} */ (new Map());
   for (const it of [...(items ?? []), ...(svcs ?? [])]) {
     totalBy.set(it.checkup_id, (totalBy.get(it.checkup_id) ?? 0) + it.line_total);
   }
@@ -94,7 +107,7 @@ export async function GET(req: Request) {
   const ws = XLSX.utils.json_to_sheet(sheetRows);
   const wb = XLSX.utils.book_new();
   XLSX.utils.book_append_sheet(wb, ws, "Visits");
-  const buffer: Buffer = XLSX.write(wb, { type: "buffer", bookType: "xlsx" });
+  const buffer = /** @type {Buffer} */ (XLSX.write(wb, { type: "buffer", bookType: "xlsx" }));
 
   return new Response(new Uint8Array(buffer), {
     headers: {
diff --git a/app/[locale]/(auth)/layout.tsx b/app/[locale]/(auth)/layout.jsx
similarity index 87%
rename from app/[locale]/(auth)/layout.tsx
rename to app/[locale]/(auth)/layout.jsx
index 9fe82d0..a2532b0 100644
--- a/app/[locale]/(auth)/layout.tsx
+++ b/app/[locale]/(auth)/layout.jsx
@@ -5,9 +5,10 @@
  * Centers the card content on the page; no sidebar, no app nav.
  * Deliberately does NOT call getServerSession() — this is a public route.
  */
-import type { ReactNode } from "react";
-
-export default function AuthLayout({ children }: { children: ReactNode }) {
+/**
+ * @param {{ children: import("react").ReactNode }} props
+ */
+export default function AuthLayout({ children }) {
   return (
     <div className="bg-background flex min-h-screen flex-col items-center justify-center px-4 py-12">
       {/* Brand mark */}
diff --git a/app/[locale]/(auth)/sign-in/actions.ts b/app/[locale]/(auth)/sign-in/actions.js
similarity index 94%
rename from app/[locale]/(auth)/sign-in/actions.ts
rename to app/[locale]/(auth)/sign-in/actions.js
index c10ea6a..f605a6b 100644
--- a/app/[locale]/(auth)/sign-in/actions.ts
+++ b/app/[locale]/(auth)/sign-in/actions.js
@@ -20,7 +20,9 @@ import { getLocale, getTranslations } from "next-intl/server";
 import { redirect } from "@/i18n/navigation";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
 import { createRateLimiter } from "@/lib/upstash";
-import { parseSignIn, type SignInState } from "@/lib/auth/schemas";
+import { parseSignIn } from "@/lib/auth/schemas";
+
+/** @typedef {import('@/lib/auth/schemas').SignInState} SignInState */
 
 // Brute-force guard on the SHARED Supabase auth quota. Keyed by client IP
 // (not email) so an attacker cannot lock a specific victim out. 5 tries / 60s.
@@ -40,10 +42,12 @@ const signInLimiter = createRateLimiter("login", 5, 60);
  *     out and return the same generic error (enumeration defense).
  *  4. redirect to /${locale}/dashboard — never returns on the success path.
  */
-export async function signInAction(
-  _prevState: SignInState,
-  formData: FormData,
-): Promise<SignInState> {
+/**
+ * @param {SignInState} _prevState
+ * @param {FormData} formData
+ * @returns {Promise<SignInState>}
+ */
+export async function signInAction(_prevState, formData) {
   const t = await getTranslations("auth.signIn");
 
   // Step 1 — schema validation
@@ -160,7 +164,10 @@ export async function signInAction(
  * The try/catch around signOut is intentional: cookie clearing is local, so
  * even if the Supabase call fails we still redirect to clear the UI state.
  */
-export async function signOutAction(): Promise<void> {
+/**
+ * @returns {Promise<void>}
+ */
+export async function signOutAction() {
   const supabase = await createSupabaseServerClient();
 
   try {
diff --git a/app/[locale]/(auth)/sign-in/page.tsx b/app/[locale]/(auth)/sign-in/page.jsx
similarity index 77%
rename from app/[locale]/(auth)/sign-in/page.tsx
rename to app/[locale]/(auth)/sign-in/page.jsx
index 2e597c6..0258d0c 100644
--- a/app/[locale]/(auth)/sign-in/page.tsx
+++ b/app/[locale]/(auth)/sign-in/page.jsx
@@ -9,11 +9,11 @@ import { redirect } from "@/i18n/navigation";
 import { getServerSession } from "@/lib/auth/get-server-session";
 import { SignInForm } from "./sign-in-form";
 
-interface SignInPageProps {
-  params: Promise<{ locale: string }>;
-}
-
-export default async function SignInPage({ params }: SignInPageProps) {
+/**
+ * @param {{ params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function SignInPage({ params }) {
   const { locale } = await params;
 
   // Redirect authenticated users away from the sign-in page.
diff --git a/app/[locale]/(auth)/sign-in/sign-in-form.tsx b/app/[locale]/(auth)/sign-in/sign-in-form.jsx
similarity index 93%
rename from app/[locale]/(auth)/sign-in/sign-in-form.tsx
rename to app/[locale]/(auth)/sign-in/sign-in-form.jsx
index 745eeba..21649eb 100644
--- a/app/[locale]/(auth)/sign-in/sign-in-form.tsx
+++ b/app/[locale]/(auth)/sign-in/sign-in-form.jsx
@@ -23,25 +23,29 @@ import { Eye, EyeOff } from "lucide-react";
 import { Button } from "@/components/ui/button";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
-import { SignInSchema, type SignInInput, type SignInState } from "@/lib/auth/schemas";
+import { SignInSchema } from "@/lib/auth/schemas";
 import { signInAction } from "./actions";
 
+/** @typedef {import('@/lib/auth/schemas').SignInInput} SignInInput */
+/** @typedef {import('@/lib/auth/schemas').SignInState} SignInState */
+
 // ---------------------------------------------------------------------------
 // Component
 // ---------------------------------------------------------------------------
 
+/** Email/password sign-in form backed by a server action. @returns {import("react").JSX.Element} */
 export function SignInForm() {
   const t = useTranslations("auth.signIn");
 
   // useActionState wires React 19's form action mechanism.
   // isPending reflects the Transition wrapping the Server Action round-trip.
-  const [state, dispatchAction, isPending] = useActionState<SignInState, FormData>(signInAction, {
+  const [state, dispatchAction, isPending] = useActionState(signInAction, {
     status: "idle",
   });
 
   // RHF: client-side Zod validation for instant inline feedback.
   // mode:"onBlur" fires validation when the user leaves a field.
-  const form = useForm<SignInInput>({
+  const form = useForm({
     resolver: zodResolver(SignInSchema),
     mode: "onBlur",
     defaultValues: { email: "", password: "" },
diff --git a/app/[locale]/error.tsx b/app/[locale]/error.jsx
similarity index 87%
rename from app/[locale]/error.tsx
rename to app/[locale]/error.jsx
index 5a8e85e..34a2f1a 100644
--- a/app/[locale]/error.tsx
+++ b/app/[locale]/error.jsx
@@ -9,7 +9,10 @@
 import { useTranslations } from "next-intl";
 import { Button } from "@/components/ui/button";
 
-export default function LocaleError({ reset }: { error: Error; reset: () => void }) {
+/**
+ * @param {{ error: Error, reset: () => void }} props
+ */
+export default function LocaleError({ reset }) {
   const t = useTranslations("errors");
   return (
     <div className="mx-auto flex min-h-[60vh] max-w-md flex-col items-center justify-center px-4 text-center">
diff --git a/app/[locale]/layout.tsx b/app/[locale]/layout.jsx
similarity index 87%
rename from app/[locale]/layout.tsx
rename to app/[locale]/layout.jsx
index 3125a5f..08fb710 100644
--- a/app/[locale]/layout.tsx
+++ b/app/[locale]/layout.jsx
@@ -5,8 +5,6 @@ import { NextIntlClientProvider, hasLocale } from "next-intl";
 import { setRequestLocale } from "next-intl/server";
 import { notFound } from "next/navigation";
 import { Be_Vietnam_Pro } from "next/font/google";
-import type { Metadata, Viewport } from "next";
-import type { ReactNode } from "react";
 import { routing } from "@/i18n/routing";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
 import { SessionProvider } from "@/lib/auth/session-provider";
@@ -23,29 +21,30 @@ const beVietnamPro = Be_Vietnam_Pro({
   display: "swap",
 });
 
-export const metadata: Metadata = {
+/** @type {import("next").Metadata} */
+export const metadata = {
   title: "BSK Clinic",
   description: "Educational clinic management rewrite",
 };
 
-export const viewport: Viewport = {
+/** @type {import("next").Viewport} */
+export const viewport = {
   themeColor: [
     { media: "(prefers-color-scheme: light)", color: "#ffffff" },
     { media: "(prefers-color-scheme: dark)", color: "#0a0a0a" },
   ],
 };
 
+/** Pre-renders one static shell per supported locale. @returns {{ locale: string }[]} */
 export function generateStaticParams() {
   return routing.locales.map((locale) => ({ locale }));
 }
 
-export default async function LocaleLayout({
-  children,
-  params,
-}: {
-  children: ReactNode;
-  params: Promise<{ locale: string }>;
-}) {
+/**
+ * @param {{ children: import("react").ReactNode, params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function LocaleLayout({ children, params }) {
   const { locale } = await params;
 
   if (!hasLocale(routing.locales, locale)) {
diff --git a/app/[locale]/not-found.tsx b/app/[locale]/not-found.jsx
similarity index 87%
rename from app/[locale]/not-found.tsx
rename to app/[locale]/not-found.jsx
index 3c70d8e..a9d3052 100644
--- a/app/[locale]/not-found.tsx
+++ b/app/[locale]/not-found.jsx
@@ -1,5 +1,8 @@
 import { getTranslations } from "next-intl/server";
 
+/**
+ * @returns {Promise<import("react").JSX.Element>}
+ */
 export default async function LocaleNotFound() {
   const t = await getTranslations("errors");
 
diff --git a/app/[locale]/page.tsx b/app/[locale]/page.jsx
similarity index 79%
rename from app/[locale]/page.tsx
rename to app/[locale]/page.jsx
index e02fb6d..8d722c6 100644
--- a/app/[locale]/page.tsx
+++ b/app/[locale]/page.jsx
@@ -1,6 +1,10 @@
 import { getTranslations, setRequestLocale } from "next-intl/server";
 
-export default async function HomePage({ params }: { params: Promise<{ locale: string }> }) {
+/**
+ * @param {{ params: Promise<{ locale: string }> }} props
+ * @returns {Promise<import("react").JSX.Element>}
+ */
+export default async function HomePage({ params }) {
   const { locale } = await params;
   // Required per next-intl static-rendering guide; intentionally duplicated
   // alongside the same call in `[locale]/layout.tsx`. Do not remove.
diff --git a/app/api/cron/nightly/route.ts b/app/api/cron/nightly/route.js
similarity index 96%
rename from app/api/cron/nightly/route.ts
rename to app/api/cron/nightly/route.js
index 652fa72..6760707 100644
--- a/app/api/cron/nightly/route.ts
+++ b/app/api/cron/nightly/route.js
@@ -17,7 +17,10 @@ export const dynamic = "force-dynamic";
 const RETENTION_DAYS = 7;
 const MEDIA_BUCKET = "bsk-checkup-media";
 
-export async function GET(req: Request) {
+/**
+ * @param {Request} req
+ */
+export async function GET(req) {
   if (!serverEnv.CRON_SECRET) {
     return new Response("CRON_SECRET not configured", { status: 503 });
   }
diff --git a/app/layout.tsx b/app/layout.jsx
similarity index 86%
rename from app/layout.tsx
rename to app/layout.jsx
index 583387a..c094050 100644
--- a/app/layout.tsx
+++ b/app/layout.jsx
@@ -1,5 +1,3 @@
-import type { ReactNode } from "react";
-
 // Intentionally empty pass-through. The real `<html>` + `<body>` live in
 // `app/[locale]/layout.tsx` so `lang={locale}` and the i18n provider can
 // be set per locale. Do not put global UI here.
@@ -13,6 +11,9 @@ import type { ReactNode } from "react";
 // render without `<html><body>`. Prefer placing `error.tsx` files under
 // `app/[locale]/` (where the real shell lives), or render the document
 // shell explicitly inside any root-level error file.
-export default function RootLayout({ children }: { children: ReactNode }) {
+/**
+ * @param {{ children: import("react").ReactNode }} props
+ */
+export default function RootLayout({ children }) {
   return children;
 }
diff --git a/app/not-found.tsx b/app/not-found.jsx
similarity index 89%
rename from app/not-found.tsx
rename to app/not-found.jsx
index 3e01517..270e6bd 100644
--- a/app/not-found.tsx
+++ b/app/not-found.jsx
@@ -3,6 +3,7 @@ import { routing } from "@/i18n/routing";
 
 // Outside-locale fallback (URL didn't match any locale segment). Renders
 // without locale context, so messages are hardcoded in both languages.
+/** Root 404 page outside the locale segment. @returns {import("react").JSX.Element} */
 export default function GlobalNotFound() {
   return (
     <html lang={routing.defaultLocale}>
diff --git a/components.json b/components.json
index 4ee62ee..6dc8745 100644
--- a/components.json
+++ b/components.json
@@ -2,7 +2,7 @@
   "$schema": "https://ui.shadcn.com/schema.json",
   "style": "new-york",
   "rsc": true,
-  "tsx": true,
+  "tsx": false,
   "tailwind": {
     "config": "",
     "css": "app/globals.css",
diff --git a/components/app-shell/app-shell-frame.tsx b/components/app-shell/app-shell-frame.jsx
similarity index 86%
rename from components/app-shell/app-shell-frame.tsx
rename to components/app-shell/app-shell-frame.jsx
index 1e94607..04bb2cf 100644
--- a/components/app-shell/app-shell-frame.tsx
+++ b/components/app-shell/app-shell-frame.jsx
@@ -13,7 +13,7 @@
  * the layout. Drawer auto-closes on route change.
  */
 
-import { useEffect, useRef, useState, type ReactNode } from "react";
+import { useEffect, useRef, useState } from "react";
 import { Menu } from "lucide-react";
 import { useTranslations } from "next-intl";
 import { usePathname } from "@/i18n/navigation";
@@ -21,17 +21,19 @@ import { usePathname } from "@/i18n/navigation";
 const DRAWER_ID = "app-mobile-drawer";
 const MAIN_ID = "main-content";
 
-type AppShellFrameProps = {
-  sidebar: ReactNode;
-  children: ReactNode;
-};
+/**
+ * @typedef {object} AppShellFrameProps
+ * @property {import("react").ReactNode} sidebar
+ * @property {import("react").ReactNode} children
+ */
 
-export function AppShellFrame({ sidebar, children }: AppShellFrameProps) {
+/** @param {AppShellFrameProps} props */
+export function AppShellFrame({ sidebar, children }) {
   const [open, setOpen] = useState(false);
   const pathname = usePathname();
   const t = useTranslations("app");
-  const drawerRef = useRef<HTMLDivElement>(null);
-  const triggerRef = useRef<HTMLButtonElement>(null);
+  const drawerRef = useRef(/** @type {HTMLDivElement | null} */ (null));
+  const triggerRef = useRef(/** @type {HTMLButtonElement | null} */ (null));
 
   // Close the drawer on route change (nav tap, redirect). Adjusting state
   // during render on a changed value is the React-recommended pattern — no
@@ -52,10 +54,12 @@ export function AppShellFrame({ sidebar, children }: AppShellFrameProps) {
     if (!drawer) return;
 
     const focusable = () =>
-      Array.from(
-        drawer.querySelectorAll<HTMLElement>(
-          'a[href],button:not([disabled]),select,input,textarea,[tabindex]:not([tabindex="-1"])',
-        ),
+      /** @type {HTMLElement[]} */ (
+        Array.from(
+          drawer.querySelectorAll(
+            'a[href],button:not([disabled]),select,input,textarea,[tabindex]:not([tabindex="-1"])',
+          ),
+        )
       );
 
     focusable()[0]?.focus();
@@ -64,7 +68,8 @@ export function AppShellFrame({ sidebar, children }: AppShellFrameProps) {
     const prevOverflow = document.body.style.overflow;
     document.body.style.overflow = "hidden";
 
-    function onKeyDown(e: KeyboardEvent) {
+    /** @param {KeyboardEvent} e */
+    function onKeyDown(e) {
       if (e.key === "Escape") {
         setOpen(false);
         return;
diff --git a/components/app-shell/app-shell.tsx b/components/app-shell/app-shell.jsx
similarity index 69%
rename from components/app-shell/app-shell.tsx
rename to components/app-shell/app-shell.jsx
index a9eec78..e2e1100 100644
--- a/components/app-shell/app-shell.tsx
+++ b/components/app-shell/app-shell.jsx
@@ -6,20 +6,20 @@
  * user info from the (app) layout which has already validated session + role.
  */
 
-import type { ReactNode } from "react";
-import type { AppRole } from "@/lib/db/roles";
 import { Sidebar } from "@/components/app-shell/sidebar";
 import { AppShellFrame } from "@/components/app-shell/app-shell-frame";
 
-type AppShellProps = {
-  email: string;
-  fullName: string | null;
-  role: AppRole;
-  locale: string;
-  children: ReactNode;
-};
+/**
+ * @typedef {object} AppShellProps
+ * @property {string} email
+ * @property {string | null} fullName
+ * @property {import("@/lib/db/roles").AppRole} role
+ * @property {string} locale
+ * @property {import("react").ReactNode} children
+ */
 
-export function AppShell({ email, fullName, role, locale, children }: AppShellProps) {
+/** @param {AppShellProps} props */
+export function AppShell({ email, fullName, role, locale, children }) {
   return (
     <AppShellFrame
       sidebar={<Sidebar email={email} fullName={fullName} role={role} locale={locale} />}
diff --git a/components/app-shell/locale-switcher.tsx b/components/app-shell/locale-switcher.jsx
similarity index 83%
rename from components/app-shell/locale-switcher.tsx
rename to components/app-shell/locale-switcher.jsx
index e58ae29..05994a1 100644
--- a/components/app-shell/locale-switcher.tsx
+++ b/components/app-shell/locale-switcher.jsx
@@ -13,6 +13,7 @@ import { useLocale, useTranslations } from "next-intl";
 import { usePathname, useRouter } from "@/i18n/navigation";
 import { routing } from "@/i18n/routing";
 
+/** Dropdown that switches the active locale while preserving the path. @returns {import("react").JSX.Element} */
 export function LocaleSwitcher() {
   const locale = useLocale();
   const router = useRouter();
@@ -22,8 +23,9 @@ export function LocaleSwitcher() {
   // slots (desktop rail + mobile drawer) — no duplicate id / label collision.
   const selectId = useId();
 
-  function handleChange(e: React.ChangeEvent<HTMLSelectElement>) {
-    const nextLocale = e.target.value as (typeof routing.locales)[number];
+  /** @param {import("react").ChangeEvent<HTMLSelectElement>} e */
+  function handleChange(e) {
+    const nextLocale = /** @type {(typeof routing.locales)[number]} */ (e.target.value);
     router.replace(pathname, { locale: nextLocale });
   }
 
diff --git a/components/app-shell/sidebar-nav.tsx b/components/app-shell/sidebar-nav.jsx
similarity index 82%
rename from components/app-shell/sidebar-nav.tsx
rename to components/app-shell/sidebar-nav.jsx
index b04258d..d73faf1 100644
--- a/components/app-shell/sidebar-nav.tsx
+++ b/components/app-shell/sidebar-nav.jsx
@@ -15,14 +15,15 @@
 import { useTranslations } from "next-intl";
 import { Link, usePathname } from "@/i18n/navigation";
 import { ROLE_MENU } from "@/lib/auth/role-menu";
-import type { AppRole } from "@/lib/db/roles";
 
-type SidebarNavProps = {
-  role: AppRole;
-  locale: string;
-};
+/**
+ * @typedef {object} SidebarNavProps
+ * @property {import("@/lib/db/roles").AppRole} role
+ * @property {string} locale
+ */
 
-export function SidebarNav({ role, locale }: SidebarNavProps) {
+/** @param {SidebarNavProps} props */
+export function SidebarNav({ role, locale }) {
   const t = useTranslations();
   const pathname = usePathname();
   const items = ROLE_MENU[role];
@@ -37,7 +38,7 @@ export function SidebarNav({ role, locale }: SidebarNavProps) {
             <li key={item.href}>
               <Link
                 href={item.href}
-                locale={locale as "vi" | "en"}
+                locale={/** @type {"vi" | "en"} */ (locale)}
                 aria-current={isActive ? "page" : undefined}
                 className={`flex min-h-11 items-center gap-2.5 rounded-md px-2.5 py-2 text-sm transition-colors ${
                   isActive
@@ -46,7 +47,7 @@ export function SidebarNav({ role, locale }: SidebarNavProps) {
                 }`}
               >
                 <Icon className="size-4 shrink-0" />
-                {t(item.labelKey as Parameters<typeof t>[0])}
+                {t(/** @type {Parameters<typeof t>[0]} */ (item.labelKey))}
               </Link>
             </li>
           );
diff --git a/components/app-shell/sidebar.tsx b/components/app-shell/sidebar.jsx
similarity index 85%
rename from components/app-shell/sidebar.tsx
rename to components/app-shell/sidebar.jsx
index 3d7e3ca..a2f38fd 100644
--- a/components/app-shell/sidebar.tsx
+++ b/components/app-shell/sidebar.jsx
@@ -7,19 +7,20 @@
  */
 
 import { getTranslations } from "next-intl/server";
-import type { AppRole } from "@/lib/db/roles";
 import { SidebarNav } from "@/components/app-shell/sidebar-nav";
 import { SignOutButton } from "@/components/app-shell/sign-out-button";
 import { LocaleSwitcher } from "@/components/app-shell/locale-switcher";
 
-type SidebarProps = {
-  email: string;
-  fullName: string | null;
-  role: AppRole;
-  locale: string;
-};
+/**
+ * @typedef {object} SidebarProps
+ * @property {string} email
+ * @property {string | null} fullName
+ * @property {import("@/lib/db/roles").AppRole} role
+ * @property {string} locale
+ */
 
-export async function Sidebar({ email, fullName, role, locale }: SidebarProps) {
+/** @param {SidebarProps} props */
+export async function Sidebar({ email, fullName, role, locale }) {
   const tRoles = await getTranslations("roles");
 
   return (
diff --git a/components/app-shell/sign-out-button.tsx b/components/app-shell/sign-out-button.jsx
similarity index 89%
rename from components/app-shell/sign-out-button.tsx
rename to components/app-shell/sign-out-button.jsx
index 4952792..a6d542d 100644
--- a/components/app-shell/sign-out-button.tsx
+++ b/components/app-shell/sign-out-button.jsx
@@ -26,6 +26,7 @@ function SignOutButtonInner() {
   );
 }
 
+/** Signs the user out via server action and redirects to sign-in. @returns {import("react").JSX.Element} */
 export function SignOutButton() {
   return (
     <form action={signOutAction}>
diff --git a/components/ui/badge.tsx b/components/ui/badge.jsx
similarity index 83%
rename from components/ui/badge.tsx
rename to components/ui/badge.jsx
index d15c436..ed07818 100644
--- a/components/ui/badge.tsx
+++ b/components/ui/badge.jsx
@@ -1,5 +1,4 @@
-import * as React from "react";
-import { cva, type VariantProps } from "class-variance-authority";
+import { cva } from "class-variance-authority";
 import { Slot } from "radix-ui";
 
 import { cn } from "@/lib/utils";
@@ -25,12 +24,12 @@ const badgeVariants = cva(
   },
 );
 
-function Badge({
-  className,
-  variant = "default",
-  asChild = false,
-  ...props
-}: React.ComponentProps<"span"> & VariantProps<typeof badgeVariants> & { asChild?: boolean }) {
+/**
+ * @param {import("react").ComponentProps<"span"> &
+ *   import("class-variance-authority").VariantProps<typeof badgeVariants> &
+ *   { asChild?: boolean }} props
+ */
+function Badge({ className, variant = "default", asChild = false, ...props }) {
   const Comp = asChild ? Slot.Root : "span";
 
   return (
diff --git a/components/ui/button.tsx b/components/ui/button.jsx
similarity index 86%
rename from components/ui/button.tsx
rename to components/ui/button.jsx
index c1e8996..a52baf6 100644
--- a/components/ui/button.tsx
+++ b/components/ui/button.jsx
@@ -1,5 +1,4 @@
-import * as React from "react";
-import { cva, type VariantProps } from "class-variance-authority";
+import { cva } from "class-variance-authority";
 import { Slot } from "radix-ui";
 
 import { cn } from "@/lib/utils";
@@ -36,16 +35,12 @@ const buttonVariants = cva(
   },
 );
 
-function Button({
-  className,
-  variant = "default",
-  size = "default",
-  asChild = false,
-  ...props
-}: React.ComponentProps<"button"> &
-  VariantProps<typeof buttonVariants> & {
-    asChild?: boolean;
-  }) {
+/**
+ * @param {import("react").ComponentProps<"button"> &
+ *   import("class-variance-authority").VariantProps<typeof buttonVariants> &
+ *   { asChild?: boolean }} props
+ */
+function Button({ className, variant = "default", size = "default", asChild = false, ...props }) {
   const Comp = asChild ? Slot.Root : "button";
 
   return (
diff --git a/components/ui/input.tsx b/components/ui/input.jsx
similarity index 88%
rename from components/ui/input.tsx
rename to components/ui/input.jsx
index 98b0001..18e7dc2 100644
--- a/components/ui/input.tsx
+++ b/components/ui/input.jsx
@@ -1,8 +1,7 @@
-import * as React from "react";
-
 import { cn } from "@/lib/utils";
 
-function Input({ className, type, ...props }: React.ComponentProps<"input">) {
+/** @param {import("react").ComponentProps<"input">} props */
+function Input({ className, type, ...props }) {
   return (
     <input
       type={type}
diff --git a/components/ui/label.tsx b/components/ui/label.jsx
similarity index 79%
rename from components/ui/label.tsx
rename to components/ui/label.jsx
index 02a62f2..a55a0cb 100644
--- a/components/ui/label.tsx
+++ b/components/ui/label.jsx
@@ -1,11 +1,11 @@
 "use client";
 
-import * as React from "react";
 import { Label as LabelPrimitive } from "radix-ui";
 
 import { cn } from "@/lib/utils";
 
-function Label({ className, ...props }: React.ComponentProps<typeof LabelPrimitive.Root>) {
+/** @param {import("react").ComponentProps<typeof LabelPrimitive.Root>} props */
+function Label({ className, ...props }) {
   return (
     <LabelPrimitive.Root
       data-slot="label"
diff --git a/components/ui/separator.tsx b/components/ui/separator.jsx
similarity index 73%
rename from components/ui/separator.tsx
rename to components/ui/separator.jsx
index 2e35219..3e69501 100644
--- a/components/ui/separator.tsx
+++ b/components/ui/separator.jsx
@@ -1,16 +1,11 @@
 "use client";
 
-import * as React from "react";
 import { Separator as SeparatorPrimitive } from "radix-ui";
 
 import { cn } from "@/lib/utils";
 
-function Separator({
-  className,
-  orientation = "horizontal",
-  decorative = true,
-  ...props
-}: React.ComponentProps<typeof SeparatorPrimitive.Root>) {
+/** @param {import("react").ComponentProps<typeof SeparatorPrimitive.Root>} props */
+function Separator({ className, orientation = "horizontal", decorative = true, ...props }) {
   return (
     <SeparatorPrimitive.Root
       data-slot="separator"
diff --git a/components/ui/sonner.tsx b/components/ui/sonner.jsx
similarity index 75%
rename from components/ui/sonner.tsx
rename to components/ui/sonner.jsx
index 28c5ec3..e29abbb 100644
--- a/components/ui/sonner.tsx
+++ b/components/ui/sonner.jsx
@@ -8,14 +8,15 @@ import {
   TriangleAlertIcon,
 } from "lucide-react";
 import { useTheme } from "next-themes";
-import { Toaster as Sonner, type ToasterProps } from "sonner";
+import { Toaster as Sonner } from "sonner";
 
-const Toaster = ({ ...props }: ToasterProps) => {
+/** @param {import("sonner").ToasterProps} props */
+const Toaster = ({ ...props }) => {
   const { theme = "system" } = useTheme();
 
   return (
     <Sonner
-      theme={theme as ToasterProps["theme"]}
+      theme={/** @type {import("sonner").ToasterProps["theme"]} */ (theme)}
       className="toaster group"
       icons={{
         success: <CircleCheckIcon className="size-4" />,
@@ -25,12 +26,12 @@ const Toaster = ({ ...props }: ToasterProps) => {
         loading: <Loader2Icon className="size-4 animate-spin" />,
       }}
       style={
-        {
+        /** @type {import("react").CSSProperties} */ ({
           "--normal-bg": "var(--popover)",
           "--normal-text": "var(--popover-foreground)",
           "--normal-border": "var(--border)",
           "--border-radius": "var(--radius)",
-        } as React.CSSProperties
+        })
       }
       {...props}
     />
diff --git a/docs/supabase-shared-config.md b/docs/supabase-shared-config.md
index 8ed45ad..c14b3f3 100644
--- a/docs/supabase-shared-config.md
+++ b/docs/supabase-shared-config.md
@@ -120,5 +120,5 @@ Channel names live in a single project-wide namespace. Prefix every channel with
 Free-tier PITR is project-wide; a restore wipes every app's data to a point in time. Per-app rollback is not supported by Supabase. Mitigations:
 
 - Daily `pg_dump --schema=bsk` cron (see `docs/runbooks/restore-from-bad-migration.md`).
-- Preflight check on migrations (see `scripts/preflight-supabase.ts`).
+- Preflight check on migrations (see `scripts/preflight-supabase.mjs`).
 - Never run destructive DDL without a recent dump.
diff --git a/eslint.config.mjs b/eslint.config.mjs
index d8d5d8a..17b8c8b 100644
--- a/eslint.config.mjs
+++ b/eslint.config.mjs
@@ -1,18 +1,25 @@
 import nextCoreWebVitals from "eslint-config-next/core-web-vitals";
-import nextTypeScript from "eslint-config-next/typescript";
 import prettier from "eslint-config-prettier";
+import jsdoc from "eslint-plugin-jsdoc";
 
 const config = [
-  { ignores: [".next/**", "node_modules/**", "dist/**", "out/**", ".vercel/**"] },
+  {
+    ignores: [
+      ".next/**",
+      "node_modules/**",
+      "dist/**",
+      "out/**",
+      ".vercel/**",
+      "coverage/**",
+      "playwright-report/**",
+      "test-results/**",
+    ],
+  },
   ...nextCoreWebVitals,
-  ...nextTypeScript,
   prettier,
   {
     rules: {
-      "@typescript-eslint/no-unused-vars": [
-        "error",
-        { argsIgnorePattern: "^_", varsIgnorePattern: "^_" },
-      ],
+      "no-unused-vars": ["error", { argsIgnorePattern: "^_", varsIgnorePattern: "^_" }],
       // Force every call site through the prefixed / schema-scoped factories.
       // Raw clients bypass the bsk:{env}: Redis prefix and the schema='bsk'
       // scoping, which collide with sibling apps sharing the same project.
@@ -40,29 +47,48 @@ const config = [
       ],
     },
   },
+  {
+    files: ["**/*.{js,jsx,mjs,cjs}"],
+    plugins: { jsdoc },
+    rules: {
+      "jsdoc/require-jsdoc": [
+        "warn",
+        {
+          publicOnly: true,
+          require: {
+            FunctionDeclaration: true,
+            FunctionExpression: true,
+            ArrowFunctionExpression: true,
+          },
+        },
+      ],
+      "jsdoc/require-param-type": "warn",
+      "jsdoc/require-returns-type": "warn",
+    },
+  },
   // Only the named factory files may import the raw infrastructure libs.
   // Explicit filenames (not a glob) keep the trust boundary tight — adding a
   // new factory should be a deliberate PR change here, not an accidental
   // file landing under `lib/supabase/*`.
   {
     files: [
-      "lib/upstash.ts",
-      "lib/supabase/server.ts",
-      "lib/supabase/client.ts",
-      "lib/supabase/admin.ts",
-      "lib/supabase/session.ts",
+      "lib/upstash.js",
+      "lib/supabase/server.js",
+      "lib/supabase/client.js",
+      "lib/supabase/admin.js",
+      "lib/supabase/session.js",
     ],
     rules: { "no-restricted-imports": "off" },
   },
   // Standalone Node scripts (seed/preflight) run outside Next and legitimately
   // build their own schema-scoped client from env — not the request factories.
   {
-    files: ["scripts/**/*.ts", "scripts/**/*.mjs"],
+    files: ["scripts/**/*.js", "scripts/**/*.mjs"],
     rules: { "no-restricted-imports": "off" },
   },
   // Test files (unit/e2e) and config files are exempt from Next.js rules.
   {
-    files: ["tests/**/*.ts", "*.config.ts", "*.config.mjs"],
+    files: ["tests/**/*.js", "*.config.js", "*.config.mjs"],
     rules: {
       "@next/next/no-html-link-for-pages": "off",
     },
diff --git a/i18n/navigation.ts b/i18n/navigation.js
similarity index 100%
rename from i18n/navigation.ts
rename to i18n/navigation.js
diff --git a/i18n/request.ts b/i18n/request.js
similarity index 100%
rename from i18n/request.ts
rename to i18n/request.js
diff --git a/i18n/routing.ts b/i18n/routing.js
similarity index 58%
rename from i18n/routing.ts
rename to i18n/routing.js
index c89e134..f154f88 100644
--- a/i18n/routing.ts
+++ b/i18n/routing.js
@@ -1,9 +1,9 @@
 import { defineRouting } from "next-intl/routing";
 
 export const routing = defineRouting({
-  locales: ["vi", "en"] as const,
+  locales: /** @type {const} */ (["vi", "en"]),
   defaultLocale: "vi",
   localePrefix: "as-needed",
 });
 
-export type Locale = (typeof routing.locales)[number];
+/** @typedef {(typeof routing.locales)[number]} Locale */
diff --git a/tsconfig.json b/jsconfig.json
similarity index 67%
rename from tsconfig.json
rename to jsconfig.json
index ae94a37..ed37be2 100644
--- a/tsconfig.json
+++ b/jsconfig.json
@@ -2,7 +2,8 @@
   "compilerOptions": {
     "target": "ES2022",
     "lib": ["dom", "dom.iterable", "esnext"],
-    "allowJs": false,
+    "allowJs": true,
+    "checkJs": true,
     "skipLibCheck": true,
     "strict": true,
     "noEmit": true,
@@ -18,7 +19,6 @@
         "name": "next"
       }
     ],
-    "baseUrl": ".",
     "paths": {
       "@/*": ["./*"]
     },
@@ -26,12 +26,15 @@
     "noUncheckedIndexedAccess": true,
     "noImplicitOverride": true
   },
-  "include": [
-    "next-env.d.ts",
-    "**/*.ts",
-    "**/*.tsx",
-    ".next/types/**/*.ts",
-    ".next/dev/types/**/*.ts"
-  ],
-  "exclude": ["node_modules", ".next/cache", ".next/dev/cache"]
+  "include": ["next-env.d.ts", "**/*.js", "**/*.jsx", "**/*.mjs", "**/*.cjs", "**/*.d.ts"],
+  "exclude": [
+    "node_modules",
+    ".next",
+    "out",
+    "dist",
+    ".vercel",
+    "coverage",
+    "playwright-report",
+    "test-results"
+  ]
 }
diff --git a/lib/auth/get-server-session.ts b/lib/auth/get-server-session.js
similarity index 74%
rename from lib/auth/get-server-session.ts
rename to lib/auth/get-server-session.js
index 4ffa591..5d9cc58 100644
--- a/lib/auth/get-server-session.ts
+++ b/lib/auth/get-server-session.js
@@ -1,20 +1,22 @@
 import "server-only";
 import { createSupabaseServerClient } from "@/lib/supabase/server";
-import { isAppRole, type AppRole } from "@/lib/db/roles";
+import { isAppRole } from "@/lib/db/roles";
+
+/** @typedef {import("@/lib/db/roles").AppRole} AppRole */
 
 // Derive the User type from the factory's return type so we never import
 // @supabase/supabase-js directly (ESLint no-restricted-imports enforces that
 // only the named factory files in lib/supabase/* may do so).
-type SupabaseServerClient = Awaited<ReturnType<typeof createSupabaseServerClient>>;
-type GetUserResult = Awaited<ReturnType<SupabaseServerClient["auth"]["getUser"]>>;
-export type User = NonNullable<GetUserResult["data"]["user"]>;
+/** @typedef {Awaited<ReturnType<typeof createSupabaseServerClient>>} SupabaseServerClient */
+/** @typedef {Awaited<ReturnType<SupabaseServerClient["auth"]["getUser"]>>} GetUserResult */
+/** @typedef {NonNullable<GetUserResult["data"]["user"]>} User */
 
-export type ServerSession = {
-  user: User;
-  role: AppRole | null;
-  /** Display name from bsk.app_users.full_name; null until an admin sets it. */
-  fullName: string | null;
-};
+/**
+ * @typedef {object} ServerSession
+ * @property {User} user
+ * @property {AppRole | null} role
+ * @property {string | null} fullName Display name from bsk.app_users.full_name; null until an admin sets it.
+ */
 
 /**
  * Reads the authenticated user and their BSK role from the current request.
@@ -31,9 +33,12 @@ export type ServerSession = {
  *
  * Used by: `[locale]/layout.tsx` (phase 02 establishes the pattern),
  * protected route layouts (phase 06), and Server Actions that need role checks.
+ *
+ * @returns {Promise<ServerSession | null>}
  */
-export async function getServerSession(): Promise<ServerSession | null> {
-  let supabase: SupabaseServerClient;
+export async function getServerSession() {
+  /** @type {SupabaseServerClient} */
+  let supabase;
 
   try {
     supabase = await createSupabaseServerClient();
@@ -59,8 +64,10 @@ export async function getServerSession(): Promise<ServerSession | null> {
   // own role — and folds the former separate full_name lookup into the same
   // round-trip. Pre-provisioning (table absent) or transient DB errors fall
   // back to role/fullName = null, never an auth failure.
-  let role: AppRole | null = null;
-  let fullName: string | null = null;
+  /** @type {AppRole | null} */
+  let role = null;
+  /** @type {string | null} */
+  let fullName = null;
 
   try {
     const { data: profile } = await supabase
diff --git a/lib/auth/invite-schema.ts b/lib/auth/invite-schema.js
similarity index 56%
rename from lib/auth/invite-schema.ts
rename to lib/auth/invite-schema.js
index 6c41e56..1012ba6 100644
--- a/lib/auth/invite-schema.ts
+++ b/lib/auth/invite-schema.js
@@ -17,24 +17,26 @@ export const InviteUserSchema = z.object({
   role: z.enum(appRoles),
 });
 
-export type InviteUserInput = z.infer<typeof InviteUserSchema>;
+/** @typedef {import("zod").infer<typeof InviteUserSchema>} InviteUserInput */
 
 // ---------------------------------------------------------------------------
 // Discriminated-union state — returned by inviteUserAction, consumed by
 // useActionState. All variants must be JSON-serializable.
 // ---------------------------------------------------------------------------
 
-export type InviteUserState =
-  | { status: "idle" }
-  | {
-      status: "error";
-      /** Per-field validation errors keyed by field name. */
-      fieldErrors: Record<string, string[]>;
-      /** Non-field error (forbidden, email taken, server error). Null when fieldErrors are set. */
-      formError: string | null;
-    }
-  | {
-      status: "success";
-      /** The email address of the newly invited user. */
-      invitedEmail: string;
-    };
+/**
+ * @typedef {object} InviteUserErrorState
+ * @property {"error"} status
+ * @property {Record<string, string[]>} fieldErrors Per-field validation errors keyed by field name.
+ * @property {string | null} formError Non-field error (forbidden, email taken, server error). Null when fieldErrors are set.
+ */
+
+/**
+ * @typedef {object} InviteUserSuccessState
+ * @property {"success"} status
+ * @property {string} invitedEmail The email address of the newly invited user.
+ */
+
+/**
+ * @typedef {{ status: "idle" } | InviteUserErrorState | InviteUserSuccessState} InviteUserState
+ */
diff --git a/lib/auth/require-role.ts b/lib/auth/require-role.js
similarity index 72%
rename from lib/auth/require-role.ts
rename to lib/auth/require-role.js
index f00993e..d2adf40 100644
--- a/lib/auth/require-role.ts
+++ b/lib/auth/require-role.js
@@ -18,13 +18,16 @@ import "server-only";
 
 import { redirect } from "@/i18n/navigation";
 import { getServerSession } from "@/lib/auth/get-server-session";
-import type { AppRole } from "@/lib/db/roles";
-import type { ServerSession } from "@/lib/auth/get-server-session";
 
-export async function requireRole(
-  allowed: AppRole[],
-  locale: string,
-): Promise<ServerSession & { role: AppRole }> {
+/** @typedef {import("@/lib/db/roles").AppRole} AppRole */
+/** @typedef {import("@/lib/auth/get-server-session").ServerSession} ServerSession */
+
+/**
+ * @param {AppRole[]} allowed
+ * @param {string} locale
+ * @returns {Promise<ServerSession & { role: AppRole }>}
+ */
+export async function requireRole(allowed, locale) {
   const session = await getServerSession();
 
   if (!session?.user) {
@@ -38,5 +41,5 @@ export async function requireRole(
     throw new Error("unreachable");
   }
 
-  return session as ServerSession & { role: AppRole };
+  return /** @type {ServerSession & { role: AppRole }} */ (session);
 }
diff --git a/lib/auth/role-menu.ts b/lib/auth/role-menu.js
similarity index 86%
rename from lib/auth/role-menu.ts
rename to lib/auth/role-menu.js
index d654b70..2dff50e 100644
--- a/lib/auth/role-menu.ts
+++ b/lib/auth/role-menu.js
@@ -12,8 +12,6 @@
  * automatically. Phase 2+ will append items for doctors, nurses, etc.
  */
 
-import type { AppRole } from "@/lib/db/roles";
-import type { ComponentType } from "react";
 import {
   LayoutDashboard,
   UserPlus,
@@ -29,14 +27,14 @@ import {
   BellRing,
 } from "lucide-react";
 
-export type MenuItem = {
-  /** Locale-relative path, e.g. "/dashboard". Sidebar prefixes with locale. */
-  href: string;
-  /** Key into the "nav" namespace in messages/{vi,en}.json */
-  labelKey: string;
-  /** Icon component from lucide-react */
-  icon: ComponentType<{ className?: string }>;
-};
+/** @typedef {import("@/lib/db/roles").AppRole} AppRole */
+
+/**
+ * @typedef {object} MenuItem
+ * @property {string} href Locale-relative path, e.g. "/dashboard". Sidebar prefixes with locale.
+ * @property {string} labelKey Key into the "nav" namespace in messages/{vi,en}.json
+ * @property {import("react").ComponentType<{ className?: string }>} icon Icon component from lucide-react
+ */
 
 /**
  * Menu items per role — Phase 1 minimal set.
@@ -48,7 +46,8 @@ export type MenuItem = {
  *   /dashboard    — this phase
  *   /admin/invite — phase 05
  */
-export const ROLE_MENU: Record<AppRole, MenuItem[]> = {
+/** @type {Record<AppRole, MenuItem[]>} */
+export const ROLE_MENU = {
   admin: [
     { href: "/dashboard", labelKey: "nav.dashboard", icon: LayoutDashboard },
     { href: "/queue", labelKey: "nav.queue", icon: ListOrdered },
diff --git a/lib/auth/schemas.ts b/lib/auth/schemas.js
similarity index 71%
rename from lib/auth/schemas.ts
rename to lib/auth/schemas.js
index 5940935..5afec1d 100644
--- a/lib/auth/schemas.ts
+++ b/lib/auth/schemas.js
@@ -18,7 +18,7 @@ export const SignInSchema = z.object({
   password: z.string().min(8).max(72),
 });
 
-export type SignInInput = z.infer<typeof SignInSchema>;
+/** @typedef {import("zod").infer<typeof SignInSchema>} SignInInput */
 
 // ---------------------------------------------------------------------------
 // Discriminated-union state — returned by signInAction, consumed by useActionState
@@ -27,15 +27,14 @@ export type SignInInput = z.infer<typeof SignInSchema>;
 // so they can cross the RSC/client boundary without crashing serialization.
 // ---------------------------------------------------------------------------
 
-export type SignInState =
-  | { status: "idle" }
-  | {
-      status: "error";
-      /** Per-field validation errors keyed by field name. */
-      fieldErrors: Record<string, string[]>;
-      /** Non-field error (auth failure, server error). Null when fieldErrors are set. */
-      formError: string | null;
-    };
+/**
+ * @typedef {object} SignInErrorState
+ * @property {"error"} status
+ * @property {Record<string, string[]>} fieldErrors Per-field validation errors keyed by field name.
+ * @property {string | null} formError Non-field error (auth failure, server error). Null when fieldErrors are set.
+ */
+
+/** @typedef {{ status: "idle" } | SignInErrorState} SignInState */
 
 // ---------------------------------------------------------------------------
 // Helper
@@ -49,17 +48,20 @@ export type SignInState =
  *
  * Extracts entries via `Object.fromEntries` — safe because FormData entries
  * here are single-value strings (email + password).
+ *
+ * @param {FormData} formData
+ * @returns {{ success: true; data: SignInInput } | { success: false; fieldErrors: Record<string, string[]> }}
  */
-export function parseSignIn(
-  formData: FormData,
-):
-  { success: true; data: SignInInput } | { success: false; fieldErrors: Record<string, string[]> } {
+export function parseSignIn(formData) {
   const result = SignInSchema.safeParse(Object.fromEntries(formData));
 
   if (!result.success) {
     // Zod v4: flatten() still produces { fieldErrors, formErrors }
     const flat = result.error.flatten();
-    return { success: false, fieldErrors: flat.fieldErrors as Record<string, string[]> };
+    return {
+      success: false,
+      fieldErrors: /** @type {Record<string, string[]>} */ (flat.fieldErrors),
+    };
   }
 
   return { success: true, data: result.data };
diff --git a/lib/auth/session-provider.tsx b/lib/auth/session-provider.jsx
similarity index 81%
rename from lib/auth/session-provider.tsx
rename to lib/auth/session-provider.jsx
index 6dffb56..1322402 100644
--- a/lib/auth/session-provider.tsx
+++ b/lib/auth/session-provider.jsx
@@ -1,12 +1,12 @@
 "use client";
 
 import { createContext, useContext } from "react";
-import type { ReactNode } from "react";
-import type { User } from "@/lib/auth/get-server-session";
+
+/** @typedef {import("@/lib/auth/get-server-session").User} User */
 
 // ── Context ───────────────────────────────────────────────────────────────────
 
-const SessionContext = createContext<User | null>(null);
+const SessionContext = createContext(/** @type {User | null} */ (null));
 
 // ── Provider ──────────────────────────────────────────────────────────────────
 
@@ -20,8 +20,10 @@ const SessionContext = createContext<User | null>(null);
  *
  * Phase 06 consumes this via `useSession()` for: sidebar user badge,
  * sign-out button, and client-side role checks.
+ *
+ * @param {{ user: User | null; children: import("react").ReactNode }} props
  */
-export function SessionProvider({ user, children }: { user: User | null; children: ReactNode }) {
+export function SessionProvider({ user, children }) {
   return <SessionContext.Provider value={user}>{children}</SessionContext.Provider>;
 }
 
@@ -30,7 +32,9 @@ export function SessionProvider({ user, children }: { user: User | null; childre
 /**
  * Returns the current authenticated user, or `null` when unauthenticated.
  * Must be called from a client component inside `<SessionProvider>`.
+ *
+ * @returns {User | null}
  */
-export function useSession(): User | null {
+export function useSession() {
   return useContext(SessionContext);
 }
diff --git a/lib/billing/dose-presets.ts b/lib/billing/dose-presets.js
similarity index 90%
rename from lib/billing/dose-presets.ts
rename to lib/billing/dose-presets.js
index 9d59b93..93e16ce 100644
--- a/lib/billing/dose-presets.ts
+++ b/lib/billing/dose-presets.js
@@ -4,7 +4,8 @@
  * routine dose. These are literal clinical shorthand — data, not UI copy —
  * so they are NOT translated via next-intl/messages.
  */
-export const dosePresets: readonly string[] = [
+/** @type {readonly string[]} */
+export const dosePresets = [
   "1 viên x 2 lần/ngày",
   "1 viên x 3 lần/ngày",
   "2 viên x 2 lần/ngày",
diff --git a/lib/billing/prescription-schema.ts b/lib/billing/prescription-schema.js
similarity index 68%
rename from lib/billing/prescription-schema.ts
rename to lib/billing/prescription-schema.js
index 0aeb041..867d097 100644
--- a/lib/billing/prescription-schema.ts
+++ b/lib/billing/prescription-schema.js
@@ -14,26 +14,32 @@ export const MedicineLineSchema = z.object({
   dosage: z.string().trim().max(200).default(""),
   notes: z.string().trim().max(500).default(""),
 });
-export type MedicineLine = z.infer<typeof MedicineLineSchema>;
+/** @typedef {import("zod").infer<typeof MedicineLineSchema>} MedicineLine */
 
 export const ServiceLineSchema = z.object({
   serviceId: z.coerce.number().int().positive(),
   quantity: z.coerce.number().int().positive().max(10_000),
 });
-export type ServiceLine = z.infer<typeof ServiceLineSchema>;
+/** @typedef {import("zod").infer<typeof ServiceLineSchema>} ServiceLine */
 
 export const MedicineLinesSchema = z.array(MedicineLineSchema).max(200);
 export const ServiceLinesSchema = z.array(ServiceLineSchema).max(200);
 
-export type PrescriptionSaveState = { status: "idle" } | { status: "error"; formError: string };
+/** @typedef {{ status: "idle" } | { status: "error"; formError: string }} PrescriptionSaveState */
 
 // ── Payment (admin/cashier) ──────────────────────────────────────────────────
-export const paymentMethods = ["cash", "card", "transfer"] as const;
-export type PaymentMethod = (typeof paymentMethods)[number];
+/** @type {readonly ["cash", "card", "transfer"]} */
+export const paymentMethods = ["cash", "card", "transfer"];
+/** @typedef {(typeof paymentMethods)[number]} PaymentMethod */
 
 export const MarkPaidSchema = z.object({
   method: z.enum(paymentMethods),
 });
 
-export type MarkPaidState =
-  { status: "idle" } | { status: "error"; formError: string } | { status: "success" };
+/**
+ * @typedef {
+ *   | { status: "idle" }
+ *   | { status: "error"; formError: string }
+ *   | { status: "success" }
+ * } MarkPaidState
+ */
diff --git a/lib/billing/totals.ts b/lib/billing/totals.js
similarity index 70%
rename from lib/billing/totals.ts
rename to lib/billing/totals.js
index af754d2..37bff25 100644
--- a/lib/billing/totals.ts
+++ b/lib/billing/totals.js
@@ -6,24 +6,31 @@
 /**
  * Sum a numeric field from an array of objects (supports both line_total and lineTotal).
  * Useful for computing totals from order_items, checkup_services, or InvoiceLine arrays.
+ *
+ * @param {Array<{ line_total?: number; lineTotal?: number } & Record<string, unknown>>} lines
+ * @returns {number}
  */
-export function sumLineTotals(
-  lines: Array<{ line_total?: number; lineTotal?: number } & Record<string, unknown>>,
-): number {
+export function sumLineTotals(lines) {
   return lines.reduce((sum, line) => sum + ((line.line_total ?? line.lineTotal) || 0), 0);
 }
 
 /**
  * Format an integer VND amount with Vietnamese locale (₫ suffix, proper grouping).
+ *
+ * @param {number} amount
+ * @returns {string}
  */
-export function formatVnd(amount: number): string {
+export function formatVnd(amount) {
   return `${new Intl.NumberFormat("vi-VN").format(amount)} ₫`;
 }
 
 /**
  * Format an integer VND amount with compact notation (K, M, B).
  * Useful for charts/dashboards with space constraints.
+ *
+ * @param {number} amount
+ * @returns {string}
  */
-export function formatVndCompact(amount: number): string {
+export function formatVndCompact(amount) {
   return new Intl.NumberFormat("vi-VN", { notation: "compact" }).format(amount);
 }
diff --git a/lib/catalog/medicine-schema.ts b/lib/catalog/medicine-schema.js
similarity index 67%
rename from lib/catalog/medicine-schema.ts
rename to lib/catalog/medicine-schema.js
index 462b414..33b58c5 100644
--- a/lib/catalog/medicine-schema.ts
+++ b/lib/catalog/medicine-schema.js
@@ -10,8 +10,11 @@ export const MedicineSchema = z.object({
   company: z.string().trim().max(200).default(""),
   route: z.string().trim().max(100).default(""),
 });
-export type MedicineInput = z.infer<typeof MedicineSchema>;
+/** @typedef {import("zod").infer<typeof MedicineSchema>} MedicineInput */
 
-export type MedicineFormState =
-  | { status: "idle" }
-  | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null };
+/**
+ * @typedef {
+ *   | { status: "idle" }
+ *   | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null }
+ * } MedicineFormState
+ */
diff --git a/lib/catalog/service-schema.js b/lib/catalog/service-schema.js
new file mode 100644
index 0000000..1f5eced
--- /dev/null
+++ b/lib/catalog/service-schema.js
@@ -0,0 +1,17 @@
+/** Zod schema + state for services. Shared client/server. Money = integer VND. */
+
+import { z } from "zod";
+
+export const ServiceSchema = z.object({
+  name: z.string().trim().min(1).max(200),
+  price: z.coerce.number().int().min(0).max(1_000_000_000).default(0),
+});
+/** @typedef {import("zod").infer<typeof ServiceSchema>} ServiceInput */
+
+/**
+ * @typedef {
+ *   | { status: "idle" }
+ *   | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null }
+ *   | { status: "success"; serviceName: string }
+ * } ServiceFormState
+ */
diff --git a/lib/catalog/service-schema.ts b/lib/catalog/service-schema.ts
deleted file mode 100644
index 8202a6d..0000000
--- a/lib/catalog/service-schema.ts
+++ /dev/null
@@ -1,14 +0,0 @@
-/** Zod schema + state for services. Shared client/server. Money = integer VND. */
-
-import { z } from "zod";
-
-export const ServiceSchema = z.object({
-  name: z.string().trim().min(1).max(200),
-  price: z.coerce.number().int().min(0).max(1_000_000_000).default(0),
-});
-export type ServiceInput = z.infer<typeof ServiceSchema>;
-
-export type ServiceFormState =
-  | { status: "idle" }
-  | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null }
-  | { status: "success"; serviceName: string };
diff --git a/lib/checkups/checkup-schema.ts b/lib/checkups/checkup-schema.js
similarity index 67%
rename from lib/checkups/checkup-schema.ts
rename to lib/checkups/checkup-schema.js
index af31c6f..e0750e4 100644
--- a/lib/checkups/checkup-schema.ts
+++ b/lib/checkups/checkup-schema.js
@@ -4,8 +4,8 @@
 
 import { z } from "zod";
 
-export const checkupStatuses = ["waiting", "in_progress", "done"] as const;
-export type CheckupStatus = (typeof checkupStatuses)[number];
+export const checkupStatuses = /** @type {const} */ (["waiting", "in_progress", "done"]);
+/** @typedef {(typeof checkupStatuses)[number]} CheckupStatus */
 
 // ── Register a patient into today's queue ────────────────────────────────────
 export const RegisterCheckupSchema = z.object({
@@ -14,22 +14,30 @@ export const RegisterCheckupSchema = z.object({
   doctorId: z.string().trim().default(""), // "" or a numeric id
   checkupType: z.string().trim().max(100).default(""),
 });
-export type RegisterCheckupInput = z.infer<typeof RegisterCheckupSchema>;
+/** @typedef {import("zod").infer<typeof RegisterCheckupSchema>} RegisterCheckupInput */
 
-export type RegisterCheckupState =
-  | { status: "idle" }
-  | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null }
-  | { status: "success"; queueNumber: number | null };
+/**
+ * @typedef {
+ *   | { status: "idle" }
+ *   | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null }
+ *   | { status: "success"; queueNumber: number | null }
+ * } RegisterCheckupState
+ */
 
 // ── Manual queue-counter override (admin/receptionist) ───────────────────────
 export const SetQueueCounterSchema = z.object({
   shiftId: z.coerce.number().int().min(1),
   value: z.coerce.number().int().min(0),
 });
-export type SetQueueCounterInput = z.infer<typeof SetQueueCounterSchema>;
+/** @typedef {import("zod").infer<typeof SetQueueCounterSchema>} SetQueueCounterInput */
 
-export type SetQueueCounterState =
-  { status: "idle" } | { status: "error"; formError: string | null } | { status: "success" };
+/**
+ * @typedef {
+ *   | { status: "idle" }
+ *   | { status: "error"; formError: string | null }
+ *   | { status: "success" }
+ * } SetQueueCounterState
+ */
 
 // ── Doctor fills the checkup ─────────────────────────────────────────────────
 const dateOrEmpty = z
@@ -52,14 +60,22 @@ export const CheckupSaveSchema = z.object({
   recheckDate: dateOrEmpty,
   status: z.enum(checkupStatuses).default("in_progress"),
 });
-export type CheckupSaveInput = z.infer<typeof CheckupSaveSchema>;
+/** @typedef {import("zod").infer<typeof CheckupSaveSchema>} CheckupSaveInput */
 
-export type CheckupSaveState =
-  | { status: "idle" }
-  | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null };
+/**
+ * @typedef {
+ *   | { status: "idle" }
+ *   | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null }
+ * } CheckupSaveState
+ */
 
-/** Text numeric field → number | null (blank/NaN → null). */
-export function parseNum(s: string): number | null {
+/**
+ * Text numeric field → number | null (blank/NaN → null).
+ *
+ * @param {string} s
+ * @returns {number | null}
+ */
+export function parseNum(s) {
   const v = s.trim();
   if (!v) return null;
   const n = Number(v);
@@ -78,16 +94,20 @@ export const TemplateValuesSchema = z
     }),
   )
   .max(50);
-export type TemplateValues = z.infer<typeof TemplateValuesSchema>;
+/** @typedef {import("zod").infer<typeof TemplateValuesSchema>} TemplateValues */
 
 /**
  * Parses the `templateValues` hidden-input JSON string. Invalid JSON or a
  * shape that fails validation is treated as "no template values" (null)
  * rather than failing the whole checkup save.
+ *
+ * @param {string} raw
+ * @returns {TemplateValues | null}
  */
-export function parseTemplateValues(raw: string): TemplateValues | null {
+export function parseTemplateValues(raw) {
   if (!raw.trim()) return null;
-  let json: unknown;
+  /** @type {unknown} */
+  let json;
   try {
     json = JSON.parse(raw);
   } catch {
diff --git a/lib/clinic/clinic-settings-schema.ts b/lib/clinic/clinic-settings-schema.js
similarity index 58%
rename from lib/clinic/clinic-settings-schema.ts
rename to lib/clinic/clinic-settings-schema.js
index a01f8f8..9e5b85d 100644
--- a/lib/clinic/clinic-settings-schema.ts
+++ b/lib/clinic/clinic-settings-schema.js
@@ -12,9 +12,12 @@ export const ClinicSettingsSchema = z.object({
   prefix: z.string().trim().max(20),
 });
 
-export type ClinicSettingsInput = z.infer<typeof ClinicSettingsSchema>;
+/** @typedef {import("zod").infer<typeof ClinicSettingsSchema>} ClinicSettingsInput */
 
-export type ClinicSettingsState =
-  | { status: "idle" }
-  | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null }
-  | { status: "success" };
+/**
+ * @typedef {
+ *   | { status: "idle" }
+ *   | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null }
+ *   | { status: "success" }
+ * } ClinicSettingsState
+ */
diff --git a/lib/customers/customer-schema.ts b/lib/customers/customer-schema.js
similarity index 63%
rename from lib/customers/customer-schema.ts
rename to lib/customers/customer-schema.js
index 8e5dc85..871c332 100644
--- a/lib/customers/customer-schema.ts
+++ b/lib/customers/customer-schema.js
@@ -5,8 +5,8 @@
 
 import { z } from "zod";
 
-export const genderValues = ["male", "female", "other"] as const;
-export type Gender = (typeof genderValues)[number];
+export const genderValues = /** @type {const} */ (["male", "female", "other"]);
+/** @typedef {(typeof genderValues)[number]} Gender */
 
 export const CustomerSchema = z.object({
   lastName: z.string().trim().min(1).max(100),
@@ -25,9 +25,12 @@ export const CustomerSchema = z.object({
   addressDetail: z.string().trim().max(300).default(""),
 });
 
-export type CustomerInput = z.infer<typeof CustomerSchema>;
+/** @typedef {import("zod").infer<typeof CustomerSchema>} CustomerInput */
 
-/** Error-or-idle state; success redirects to the list, so there's no success variant. */
-export type CustomerFormState =
-  | { status: "idle" }
-  | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null };
+/**
+ * Error-or-idle state; success redirects to the list, so there's no success variant.
+ * @typedef {
+ *   | { status: "idle" }
+ *   | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null }
+ * } CustomerFormState
+ */
diff --git a/lib/db/roles.ts b/lib/db/roles.js
similarity index 64%
rename from lib/db/roles.ts
rename to lib/db/roles.js
index 87898b4..a228926 100644
--- a/lib/db/roles.ts
+++ b/lib/db/roles.js
@@ -7,25 +7,33 @@
  * the generated database types at typecheck time — no runtime cost.
  */
 
-import type { Database } from "@/types/supabase-bsk";
-
 // Ordered tuple — used for iteration (dropdowns, role-badge maps, etc.)
-export const appRoles = ["admin", "doctor", "nurse", "receptionist", "cashier", "patient"] as const;
+export const appRoles = /** @type {const} */ ([
+  "admin",
+  "doctor",
+  "nurse",
+  "receptionist",
+  "cashier",
+  "patient",
+]);
 
-/** Union of all valid BSK role strings, derived from the tuple above. */
-export type AppRole = (typeof appRoles)[number];
+/** Union of all valid BSK role strings, derived from the tuple above. @typedef {(typeof appRoles)[number]} AppRole */
 
 /**
  * Compile-time guard: if the database enum and this tuple ever diverge,
  * typecheck fails here — not at a runtime crash in production.
+ * @type {import("@/types/supabase-bsk").Database["bsk"]["Enums"]["app_role"][]}
  */
-const _roleGuard: AppRole[] = [] satisfies Database["bsk"]["Enums"]["app_role"][];
+const _roleGuard = [...appRoles];
 void _roleGuard; // prevent unused-variable lint warning
 
 /**
  * Returns true if `s` is a valid `AppRole` value.
  * Use as a type-narrowing guard when validating external input.
+ *
+ * @param {string} s
+ * @returns {s is AppRole}
  */
-export function isAppRole(s: string): s is AppRole {
-  return (appRoles as readonly string[]).includes(s);
+export function isAppRole(s) {
+  return /** @type {readonly string[]} */ (appRoles).includes(s);
 }
diff --git a/lib/doctors/doctor-schema.ts b/lib/doctors/doctor-schema.js
similarity index 52%
rename from lib/doctors/doctor-schema.ts
rename to lib/doctors/doctor-schema.js
index ca36304..14401c7 100644
--- a/lib/doctors/doctor-schema.ts
+++ b/lib/doctors/doctor-schema.js
@@ -12,10 +12,13 @@ export const DoctorSchema = z.object({
   lastName: z.string().trim().min(1).max(100),
 });
 
-export type DoctorInput = z.infer<typeof DoctorSchema>;
+/** @typedef {import("zod").infer<typeof DoctorSchema>} DoctorInput */
 
-/** useActionState shape for the add-doctor form. JSON-serializable. */
-export type DoctorFormState =
-  | { status: "idle" }
-  | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null }
-  | { status: "success"; doctorName: string };
+/**
+ * useActionState shape for the add-doctor form. JSON-serializable.
+ * @typedef {
+ *   | { status: "idle" }
+ *   | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null }
+ *   | { status: "success"; doctorName: string }
+ * } DoctorFormState
+ */
diff --git a/lib/env/client.ts b/lib/env/client.js
similarity index 87%
rename from lib/env/client.ts
rename to lib/env/client.js
index 28ea7b7..cd7b761 100644
--- a/lib/env/client.ts
+++ b/lib/env/client.js
@@ -21,5 +21,7 @@ if (!parsed.success) {
 
 export const clientEnv = parsed.data;
 
-export const APP_SLUG = "bsk" as const;
-export const SUPABASE_SCHEMA = "bsk" as const;
+/** @type {"bsk"} */
+export const APP_SLUG = "bsk";
+/** @type {"bsk"} */
+export const SUPABASE_SCHEMA = "bsk";
diff --git a/lib/env/server.ts b/lib/env/server.js
similarity index 92%
rename from lib/env/server.ts
rename to lib/env/server.js
index 39c8997..7bf6169 100644
--- a/lib/env/server.ts
+++ b/lib/env/server.js
@@ -2,11 +2,12 @@ import "server-only";
 import { z } from "zod";
 import { APP_SLUG, SUPABASE_SCHEMA, clientEnv } from "./client";
 
+/** @type {{ production: "prod"; preview: "preview"; development: "dev" }} */
 const VERCEL_TO_APP_ENV = {
   production: "prod",
   preview: "preview",
   development: "dev",
-} as const;
+};
 
 const serverSchema = z
   .object({
@@ -58,4 +59,5 @@ export const serverEnv = {
 };
 
 export { APP_SLUG, SUPABASE_SCHEMA };
-export const redisKeyPrefix = `${APP_SLUG}:${clientEnv.NEXT_PUBLIC_APP_ENV}` as const;
+/** @type {`${typeof APP_SLUG}:${typeof clientEnv.NEXT_PUBLIC_APP_ENV}`} */
+export const redisKeyPrefix = `${APP_SLUG}:${clientEnv.NEXT_PUBLIC_APP_ENV}`;
diff --git a/lib/imaging/image-schema.ts b/lib/imaging/image-schema.js
similarity index 75%
rename from lib/imaging/image-schema.ts
rename to lib/imaging/image-schema.js
index 7292862..0c2a08a 100644
--- a/lib/imaging/image-schema.ts
+++ b/lib/imaging/image-schema.js
@@ -14,8 +14,13 @@ export const SIGNED_URL_TTL_SECONDS = 60 * 60; // 1 hour
 
 const UUID_JPG = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}\.jpg$/i;
 
-/** Builds the object key for an uploaded image — `{checkupId}/{uuid}.jpg`. */
-export function buildStoragePath(checkupId: number, uuid: string): string {
+/**
+ * Builds the object key for an uploaded image — `{checkupId}/{uuid}.jpg`.
+ * @param {number} checkupId
+ * @param {string} uuid
+ * @returns {string}
+ */
+export function buildStoragePath(checkupId, uuid) {
   return `${checkupId}/${uuid}.jpg`;
 }
 
@@ -23,8 +28,12 @@ export function buildStoragePath(checkupId: number, uuid: string): string {
  * Validates that a storage path belongs to the given checkup and matches the
  * `{uuid}.jpg` naming convention. Prevents a client from recording metadata
  * that points at an object under a different checkup (or an arbitrary key).
+ *
+ * @param {number} checkupId
+ * @param {string} path
+ * @returns {boolean}
  */
-export function isValidStoragePath(checkupId: number, path: string): boolean {
+export function isValidStoragePath(checkupId, path) {
   const parts = path.split("/");
   if (parts.length !== 2 || parts[0] !== String(checkupId)) return false;
   const filename = parts[1] ?? "";
@@ -42,5 +51,10 @@ export const DeleteImageSchema = z.object({
   storagePath: z.string().trim().min(1).max(300),
 });
 
-export type ImageActionState =
-  { status: "idle" } | { status: "error"; message: string } | { status: "success" };
+/**
+ * @typedef {
+ *   | { status: "idle" }
+ *   | { status: "error"; message: string }
+ *   | { status: "success" }
+ * } ImageActionState
+ */
diff --git a/lib/pdf/fonts.ts b/lib/pdf/fonts.js
similarity index 93%
rename from lib/pdf/fonts.ts
rename to lib/pdf/fonts.js
index f3b907d..fc11556 100644
--- a/lib/pdf/fonts.ts
+++ b/lib/pdf/fonts.js
@@ -10,7 +10,8 @@ import { Font } from "@react-pdf/renderer";
  */
 let registered = false;
 
-export function registerPdfFonts(): void {
+/** @returns {void} */
+export function registerPdfFonts() {
   if (registered) return;
   Font.register({
     family: "Be Vietnam Pro",
diff --git a/lib/pdf/invoice-document.tsx b/lib/pdf/invoice-document.jsx
similarity index 69%
rename from lib/pdf/invoice-document.tsx
rename to lib/pdf/invoice-document.jsx
index 3cf28c6..7de276b 100644
--- a/lib/pdf/invoice-document.tsx
+++ b/lib/pdf/invoice-document.jsx
@@ -3,37 +3,45 @@ import { registerPdfFonts } from "./fonts";
 
 /** Server-rendered invoice PDF (Be Vietnam Pro registered via registerPdfFonts). */
 
-export type InvoiceLine = { name: string; quantity: number; unitPrice: number; lineTotal: number };
+/**
+ * @typedef {object} InvoiceLine
+ * @property {string} name
+ * @property {number} quantity
+ * @property {number} unitPrice
+ * @property {number} lineTotal
+ */
 
-export type InvoiceData = {
-  clinicName: string;
-  clinicAddress: string;
-  clinicPhone: string;
-  patientName: string;
-  date: string;
-  queueNumber: number | null;
-  medicines: InvoiceLine[];
-  services: InvoiceLine[];
-  total: number;
-  paid: boolean;
-  labels: {
-    invoice: string;
-    patient: string;
-    date: string;
-    queue: string;
-    medicines: string;
-    services: string;
-    item: string;
-    qty: string;
-    unitPrice: string;
-    lineTotal: string;
-    total: string;
-    paid: string;
-    unpaid: string;
-  };
-};
+/**
+ * @typedef {object} InvoiceData
+ * @property {string} clinicName
+ * @property {string} clinicAddress
+ * @property {string} clinicPhone
+ * @property {string} patientName
+ * @property {string} date
+ * @property {number | null} queueNumber
+ * @property {InvoiceLine[]} medicines
+ * @property {InvoiceLine[]} services
+ * @property {number} total
+ * @property {boolean} paid
+ * @property {{
+ *   invoice: string;
+ *   patient: string;
+ *   date: string;
+ *   queue: string;
+ *   medicines: string;
+ *   services: string;
+ *   item: string;
+ *   qty: string;
+ *   unitPrice: string;
+ *   lineTotal: string;
+ *   total: string;
+ *   paid: string;
+ *   unpaid: string;
+ * }} labels
+ */
 
-const vnd = (n: number) => `${new Intl.NumberFormat("vi-VN").format(n)} ₫`;
+/** @param {number} n */
+const vnd = (n) => `${new Intl.NumberFormat("vi-VN").format(n)} ₫`;
 
 const s = StyleSheet.create({
   page: { fontFamily: "Be Vietnam Pro", fontSize: 10, padding: 36, color: "#111" },
@@ -65,15 +73,10 @@ const s = StyleSheet.create({
   status: { marginTop: 10, textAlign: "right", fontSize: 10 },
 });
 
-function Table({
-  title,
-  rows,
-  L,
-}: {
-  title: string;
-  rows: InvoiceLine[];
-  L: InvoiceData["labels"];
-}) {
+/**
+ * @param {{ title: string; rows: InvoiceLine[]; L: InvoiceData["labels"] }} props
+ */
+function Table({ title, rows, L }) {
   if (rows.length === 0) return null;
   return (
     <View>
@@ -96,7 +99,8 @@ function Table({
   );
 }
 
-export function InvoiceDocument({ data }: { data: InvoiceData }) {
+/** @param {{ data: InvoiceData }} props */
+export function InvoiceDocument({ data }) {
   const L = data.labels;
   return (
     <Document>
@@ -128,8 +132,12 @@ export function InvoiceDocument({ data }: { data: InvoiceData }) {
   );
 }
 
-/** Render the invoice to a PDF Buffer (Node runtime). Registers fonts first. */
-export async function renderInvoicePdf(data: InvoiceData): Promise<Buffer> {
+/**
+ * Render the invoice to a PDF Buffer (Node runtime). Registers fonts first.
+ * @param {InvoiceData} data
+ * @returns {Promise<Buffer>}
+ */
+export async function renderInvoicePdf(data) {
   registerPdfFonts();
   return renderToBuffer(<InvoiceDocument data={data} />);
 }
diff --git a/lib/pdf/patient-info.ts b/lib/pdf/patient-info.js
similarity index 84%
rename from lib/pdf/patient-info.ts
rename to lib/pdf/patient-info.js
index 466f4ef..3f833b2 100644
--- a/lib/pdf/patient-info.ts
+++ b/lib/pdf/patient-info.js
@@ -7,8 +7,12 @@ import "server-only";
  * treats as "today".
  */
 
-/** Computes whole years of age from an ISO `YYYY-MM-DD` dob. Null if dob is null/invalid. */
-export function computeAge(dob: string | null): number | null {
+/**
+ * Computes whole years of age from an ISO `YYYY-MM-DD` dob. Null if dob is null/invalid.
+ * @param {string | null} dob
+ * @returns {number | null}
+ */
+export function computeAge(dob) {
   if (!dob) return null;
   const match = /^(\d{4})-(\d{2})-(\d{2})$/.exec(dob);
   if (!match) return null;
diff --git a/lib/pdf/prescription-document.tsx b/lib/pdf/prescription-document.jsx
similarity index 73%
rename from lib/pdf/prescription-document.tsx
rename to lib/pdf/prescription-document.jsx
index ae0b0b4..b5fb9d3 100644
--- a/lib/pdf/prescription-document.tsx
+++ b/lib/pdf/prescription-document.jsx
@@ -7,42 +7,44 @@ import { registerPdfFonts } from "./fonts";
  * dosage column is the whole point of a prescription.
  */
 
-export type PrescriptionMedicineLine = {
-  name: string;
-  unit: string | null;
-  quantity: number;
-  dosage: string;
-};
+/**
+ * @typedef {object} PrescriptionMedicineLine
+ * @property {string} name
+ * @property {string | null} unit
+ * @property {number} quantity
+ * @property {string} dosage
+ */
 
-export type PrescriptionData = {
-  clinicName: string;
-  clinicAddress: string;
-  clinicPhone: string;
-  patientName: string;
-  patientDob: string | null;
-  patientAge: number | null;
-  patientGender: string | null;
-  patientAddress: string | null;
-  date: string;
-  diagnosis: string | null;
-  doctorName: string | null;
-  medicines: PrescriptionMedicineLine[];
-  labels: {
-    prescription: string;
-    patient: string;
-    date: string;
-    dob: string;
-    age: string;
-    gender: string;
-    address: string;
-    diagnosis: string;
-    item: string;
-    qty: string;
-    dosage: string;
-    doctor: string;
-    signature: string;
-  };
-};
+/**
+ * @typedef {object} PrescriptionData
+ * @property {string} clinicName
+ * @property {string} clinicAddress
+ * @property {string} clinicPhone
+ * @property {string} patientName
+ * @property {string | null} patientDob
+ * @property {number | null} patientAge
+ * @property {string | null} patientGender
+ * @property {string | null} patientAddress
+ * @property {string} date
+ * @property {string | null} diagnosis
+ * @property {string | null} doctorName
+ * @property {PrescriptionMedicineLine[]} medicines
+ * @property {{
+ *   prescription: string;
+ *   patient: string;
+ *   date: string;
+ *   dob: string;
+ *   age: string;
+ *   gender: string;
+ *   address: string;
+ *   diagnosis: string;
+ *   item: string;
+ *   qty: string;
+ *   dosage: string;
+ *   doctor: string;
+ *   signature: string;
+ * }} labels
+ */
 
 const s = StyleSheet.create({
   page: { fontFamily: "Be Vietnam Pro", fontSize: 10, padding: 36, color: "#111" },
@@ -76,13 +78,10 @@ const s = StyleSheet.create({
   signatureName: { fontWeight: "bold", marginTop: 4 },
 });
 
-function MedicineTable({
-  rows,
-  L,
-}: {
-  rows: PrescriptionMedicineLine[];
-  L: PrescriptionData["labels"];
-}) {
+/**
+ * @param {{ rows: PrescriptionMedicineLine[]; L: PrescriptionData["labels"] }} props
+ */
+function MedicineTable({ rows, L }) {
   if (rows.length === 0) return null;
   return (
     <View>
@@ -104,7 +103,8 @@ function MedicineTable({
   );
 }
 
-export function PrescriptionDocument({ data }: { data: PrescriptionData }) {
+/** @param {{ data: PrescriptionData }} props */
+export function PrescriptionDocument({ data }) {
   const L = data.labels;
   return (
     <Document>
@@ -159,8 +159,12 @@ export function PrescriptionDocument({ data }: { data: PrescriptionData }) {
   );
 }
 
-/** Render the prescription to a PDF Buffer (Node runtime). Registers fonts first. */
-export async function renderPrescriptionPdf(data: PrescriptionData): Promise<Buffer> {
+/**
+ * Render the prescription to a PDF Buffer (Node runtime). Registers fonts first.
+ * @param {PrescriptionData} data
+ * @returns {Promise<Buffer>}
+ */
+export async function renderPrescriptionPdf(data) {
   registerPdfFonts();
   return renderToBuffer(<PrescriptionDocument data={data} />);
 }
diff --git a/lib/pdf/ultrasound-document.tsx b/lib/pdf/ultrasound-document.jsx
similarity index 76%
rename from lib/pdf/ultrasound-document.tsx
rename to lib/pdf/ultrasound-document.jsx
index 16baabd..5d7056e 100644
--- a/lib/pdf/ultrasound-document.tsx
+++ b/lib/pdf/ultrasound-document.jsx
@@ -8,34 +8,39 @@ import { registerPdfFonts } from "./fonts";
  * time in every runtime, so the route handler fetches the bytes first.
  */
 
-export type UltrasoundImage = { data: Buffer; format: "jpg" | "png" };
+/**
+ * @typedef {object} UltrasoundImage
+ * @property {Buffer} data
+ * @property {"jpg" | "png"} format
+ */
 
-export type UltrasoundData = {
-  clinicName: string;
-  clinicAddress: string;
-  clinicPhone: string;
-  title: string;
-  patientName: string;
-  patientDob: string | null;
-  patientAge: number | null;
-  patientGender: string | null;
-  date: string;
-  diagnosis: string | null;
-  conclusion: string | null;
-  doctorName: string | null;
-  images: UltrasoundImage[];
-  labels: {
-    patient: string;
-    date: string;
-    dob: string;
-    age: string;
-    gender: string;
-    diagnosis: string;
-    conclusion: string;
-    doctor: string;
-    signature: string;
-  };
-};
+/**
+ * @typedef {object} UltrasoundData
+ * @property {string} clinicName
+ * @property {string} clinicAddress
+ * @property {string} clinicPhone
+ * @property {string} title
+ * @property {string} patientName
+ * @property {string | null} patientDob
+ * @property {number | null} patientAge
+ * @property {string | null} patientGender
+ * @property {string} date
+ * @property {string | null} diagnosis
+ * @property {string | null} conclusion
+ * @property {string | null} doctorName
+ * @property {UltrasoundImage[]} images
+ * @property {{
+ *   patient: string;
+ *   date: string;
+ *   dob: string;
+ *   age: string;
+ *   gender: string;
+ *   diagnosis: string;
+ *   conclusion: string;
+ *   doctor: string;
+ *   signature: string;
+ * }} labels
+ */
 
 const s = StyleSheet.create({
   page: { fontFamily: "Be Vietnam Pro", fontSize: 10, padding: 36, color: "#111" },
@@ -56,7 +61,8 @@ const s = StyleSheet.create({
   signatureName: { fontWeight: "bold", marginTop: 4 },
 });
 
-export function UltrasoundDocument({ data }: { data: UltrasoundData }) {
+/** @param {{ data: UltrasoundData }} props */
+export function UltrasoundDocument({ data }) {
   const L = data.labels;
   return (
     <Document>
@@ -122,8 +128,12 @@ export function UltrasoundDocument({ data }: { data: UltrasoundData }) {
   );
 }
 
-/** Render the ultrasound report to a PDF Buffer (Node runtime). Registers fonts first. */
-export async function renderUltrasoundPdf(data: UltrasoundData): Promise<Buffer> {
+/**
+ * Render the ultrasound report to a PDF Buffer (Node runtime). Registers fonts first.
+ * @param {UltrasoundData} data
+ * @returns {Promise<Buffer>}
+ */
+export async function renderUltrasoundPdf(data) {
   registerPdfFonts();
   return renderToBuffer(<UltrasoundDocument data={data} />);
 }
diff --git a/lib/proxy/copy-cookies.ts b/lib/proxy/copy-cookies.js
similarity index 77%
rename from lib/proxy/copy-cookies.ts
rename to lib/proxy/copy-cookies.js
index 52a39ce..91ea6f5 100644
--- a/lib/proxy/copy-cookies.ts
+++ b/lib/proxy/copy-cookies.js
@@ -1,5 +1,3 @@
-import type { NextResponse } from "next/server";
-
 /**
  * Copies all Set-Cookie entries from `from` onto `to`.
  *
@@ -8,8 +6,12 @@ import type { NextResponse } from "next/server";
  * Specifically: Supabase session-refresh writes sb-* cookies onto a response;
  * if next-intl then produces its own redirect/rewrite response, we must port
  * the Supabase cookies onto it before returning or the auth token is lost.
+ *
+ * @param {import("next/server").NextResponse} from
+ * @param {import("next/server").NextResponse} to
+ * @returns {void}
  */
-export function copyCookies(from: NextResponse, to: NextResponse): void {
+export function copyCookies(from, to) {
   for (const cookie of from.cookies.getAll()) {
     to.cookies.set(cookie.name, cookie.value, cookie);
   }
diff --git a/lib/supabase/admin.ts b/lib/supabase/admin.js
similarity index 100%
rename from lib/supabase/admin.ts
rename to lib/supabase/admin.js
diff --git a/lib/supabase/client.ts b/lib/supabase/client.js
similarity index 72%
rename from lib/supabase/client.ts
rename to lib/supabase/client.js
index 579f202..729945a 100644
--- a/lib/supabase/client.ts
+++ b/lib/supabase/client.js
@@ -1,6 +1,7 @@
 import { createBrowserClient } from "@supabase/ssr";
 import { clientEnv, SUPABASE_SCHEMA } from "@/lib/env/client";
 
+/** Browser Supabase client scoped to the bsk schema. Return type stays inferred so realtime/query generics flow to callers. */
 export function createSupabaseBrowserClient() {
   return createBrowserClient(
     clientEnv.NEXT_PUBLIC_SUPABASE_URL,
diff --git a/lib/supabase/server.ts b/lib/supabase/server.js
similarity index 100%
rename from lib/supabase/server.ts
rename to lib/supabase/server.js
diff --git a/lib/supabase/session.ts b/lib/supabase/session.js
similarity index 83%
rename from lib/supabase/session.ts
rename to lib/supabase/session.js
index 3e95d2b..cea31b3 100644
--- a/lib/supabase/session.ts
+++ b/lib/supabase/session.js
@@ -1,16 +1,16 @@
 import "server-only";
 import { createServerClient } from "@supabase/ssr";
-import { NextResponse, type NextRequest } from "next/server";
+import { NextResponse } from "next/server";
 import { serverEnv, SUPABASE_SCHEMA } from "@/lib/env/server";
-import type { User } from "@supabase/supabase-js";
 
 /**
  * Coarse list of path prefixes that require authentication.
  * Checked by proxy.ts AFTER stripping the locale segment.
  * Extend here as new protected route groups are added (phases 05–06).
  * `/sign-in` is intentionally absent — it must be reachable while unauth'd.
+ * @type {ReadonlyArray<string>}
  */
-export const PROTECTED_PATH_PREFIXES: ReadonlyArray<string> = ["/dashboard", "/admin"];
+export const PROTECTED_PATH_PREFIXES = ["/dashboard", "/admin"];
 
 /**
  * Refreshes the Supabase auth session for an incoming request.
@@ -28,10 +28,11 @@ export const PROTECTED_PATH_PREFIXES: ReadonlyArray<string> = ["/dashboard", "/a
  * outage should not hard-fail every request. The caller treats `user: null` as
  * unauthenticated and applies the protected-path redirect; Supabase cookies are
  * preserved so the next request retries. (Confirmed acceptable — code-reviewer N6.)
+ *
+ * @param {import("next/server").NextRequest} request
+ * @returns {Promise<{ response: NextResponse; user: import("@supabase/supabase-js").User | null }>}
  */
-export async function updateSupabaseSession(
-  request: NextRequest,
-): Promise<{ response: NextResponse; user: User | null }> {
+export async function updateSupabaseSession(request) {
   const response = NextResponse.next({ request });
 
   const supabase = createServerClient(
@@ -55,7 +56,8 @@ export async function updateSupabaseSession(
     },
   );
 
-  let user: User | null = null;
+  /** @type {import("@supabase/supabase-js").User | null} */
+  let user = null;
 
   try {
     const { data } = await supabase.auth.getUser();
diff --git a/lib/templates/template-schema.js b/lib/templates/template-schema.js
new file mode 100644
index 0000000..5b9e8c7
--- /dev/null
+++ b/lib/templates/template-schema.js
@@ -0,0 +1,65 @@
+/**
+ * Zod schema + state for checkup templates. Shared client/server.
+ * `fieldsText` is one field label per line in the UI; the action serializes it
+ * to the jsonb [{ label }] layout.
+ */
+
+import { z } from "zod";
+
+export const templateGenders = /** @type {const} */ (["any", "male", "female", "other"]);
+/** @typedef {(typeof templateGenders)[number]} TemplateGender */
+
+export const TemplateSchema = z.object({
+  name: z.string().trim().min(1).max(150),
+  title: z.string().trim().max(200).default(""),
+  gender: z.enum(templateGenders).default("any"),
+  photoNum: z.coerce.number().int().min(0).max(50).default(0),
+  fieldsText: z.string().max(5000).default(""),
+});
+
+/** @typedef {import("zod").infer<typeof TemplateSchema>} TemplateInput */
+
+/**
+ * @typedef {
+ *   | { status: "idle" }
+ *   | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null }
+ * } TemplateFormState
+ */
+
+/**
+ * Split the textarea into an ordered [{ label }] layout (blank lines dropped).
+ * @param {string} text
+ * @returns {{ label: string }[]}
+ */
+export function fieldsTextToJson(text) {
+  return text
+    .split(/\r?\n/)
+    .map((l) => l.trim())
+    .filter(Boolean)
+    .map((label) => ({ label }));
+}
+
+/**
+ * Inverse: render a stored layout back to one-label-per-line text for editing.
+ * @param {unknown} fields
+ * @returns {string}
+ */
+export function fieldsJsonToText(fields) {
+  return fieldsJsonToLabels(fields).join("\n");
+}
+
+/**
+ * Extract just the ordered labels from a stored `fields` layout.
+ * @param {unknown} fields
+ * @returns {string[]}
+ */
+export function fieldsJsonToLabels(fields) {
+  if (!Array.isArray(fields)) return [];
+  return fields
+    .map((f) =>
+      f && typeof f === "object" && "label" in f
+        ? String(/** @type {{ label: unknown }} */ (f).label)
+        : "",
+    )
+    .filter(Boolean);
+}
diff --git a/lib/templates/template-schema.ts b/lib/templates/template-schema.ts
deleted file mode 100644
index f0cb2cb..0000000
--- a/lib/templates/template-schema.ts
+++ /dev/null
@@ -1,48 +0,0 @@
-/**
- * Zod schema + state for checkup templates. Shared client/server.
- * `fieldsText` is one field label per line in the UI; the action serializes it
- * to the jsonb [{ label }] layout.
- */
-
-import { z } from "zod";
-
-export const templateGenders = ["any", "male", "female", "other"] as const;
-export type TemplateGender = (typeof templateGenders)[number];
-
-export const TemplateSchema = z.object({
-  name: z.string().trim().min(1).max(150),
-  title: z.string().trim().max(200).default(""),
-  gender: z.enum(templateGenders).default("any"),
-  photoNum: z.coerce.number().int().min(0).max(50).default(0),
-  fieldsText: z.string().max(5000).default(""),
-});
-
-export type TemplateInput = z.infer<typeof TemplateSchema>;
-
-export type TemplateFormState =
-  | { status: "idle" }
-  | { status: "error"; fieldErrors: Record<string, string[]>; formError: string | null };
-
-/** Split the textarea into an ordered [{ label }] layout (blank lines dropped). */
-export function fieldsTextToJson(text: string): { label: string }[] {
-  return text
-    .split(/\r?\n/)
-    .map((l) => l.trim())
-    .filter(Boolean)
-    .map((label) => ({ label }));
-}
-
-/** Inverse: render a stored layout back to one-label-per-line text for editing. */
-export function fieldsJsonToText(fields: unknown): string {
-  return fieldsJsonToLabels(fields).join("\n");
-}
-
-/** Extract just the ordered labels from a stored `fields` layout. */
-export function fieldsJsonToLabels(fields: unknown): string[] {
-  if (!Array.isArray(fields)) return [];
-  return fields
-    .map((f) =>
-      f && typeof f === "object" && "label" in f ? String((f as { label: unknown }).label) : "",
-    )
-    .filter(Boolean);
-}
diff --git a/lib/upstash.ts b/lib/upstash.js
similarity index 72%
rename from lib/upstash.ts
rename to lib/upstash.js
index af55843..65f1ca1 100644
--- a/lib/upstash.ts
+++ b/lib/upstash.js
@@ -16,14 +16,21 @@ const KEY_RE = /^[a-z0-9][a-z0-9:-]*$/;
 // SCAN patterns allow '*' for sweeps but are otherwise constrained.
 const SCAN_PATTERN_RE = /^[a-z0-9:*-]+$/;
 
-type Json = string | number | boolean | null | { [k: string]: Json } | Json[];
+/** @typedef {string | number | boolean | null | JsonMap | JsonArray} Json */
+/** @typedef {{ [k: string]: Json }} JsonMap */
+/** @typedef {Json[]} JsonArray */
 
 const redis = new Redis({
   url: serverEnv.UPSTASH_REDIS_REST_URL,
   token: serverEnv.UPSTASH_REDIS_REST_TOKEN,
 });
 
-function withPrefix(ns: string, key: string) {
+/**
+ * @param {string} ns
+ * @param {string} key
+ * @returns {string}
+ */
+function withPrefix(ns, key) {
   if (!KEY_RE.test(key)) {
     throw new Error(
       `Invalid cache key (lowercase + digits + '-' + ':' only, must start with alphanumeric): ${JSON.stringify(key)}`,
@@ -32,7 +39,12 @@ function withPrefix(ns: string, key: string) {
   return `${redisKeyPrefix}:${ns}:${key}`;
 }
 
-function withScanPattern(ns: string, pattern: string) {
+/**
+ * @param {string} ns
+ * @param {string} pattern
+ * @returns {string}
+ */
+function withScanPattern(ns, pattern) {
   if (!SCAN_PATTERN_RE.test(pattern)) {
     throw new Error(`Invalid SCAN pattern: ${JSON.stringify(pattern)}`);
   }
@@ -40,16 +52,30 @@ function withScanPattern(ns: string, pattern: string) {
 }
 
 export const cache = {
-  async get<T extends Json>(key: string): Promise<T | null> {
-    return redis.get<T>(withPrefix(CACHE_NS, key));
+  /**
+   * @template {Json} T
+   * @param {string} key
+   * @returns {Promise<T | null>}
+   */
+  async get(key) {
+    return redis.get(withPrefix(CACHE_NS, key));
   },
-  async set(key: string, value: Json, opts?: { ex?: number }) {
+  /**
+   * @param {string} key
+   * @param {Json} value
+   * @param {{ ex?: number }} [opts]
+   */
+  async set(key, value, opts) {
     if (opts?.ex !== undefined) {
       return redis.set(withPrefix(CACHE_NS, key), value, { ex: opts.ex });
     }
     return redis.set(withPrefix(CACHE_NS, key), value);
   },
-  async del(key: string, ...rest: string[]) {
+  /**
+   * @param {string} key
+   * @param {...string} rest
+   */
+  async del(key, ...rest) {
     const keys = [key, ...rest];
     return redis.del(...keys.map((k) => withPrefix(CACHE_NS, k)));
   },
@@ -57,8 +83,11 @@ export const cache = {
    * Iterate the BSK cache namespace. `matchSuffix` is appended to the
    * `bsk:{env}:cache:` prefix; keep it as narrow as possible — `"*"` sweeps
    * the entire BSK cache and should only be used in admin tools.
+   *
+   * @param {string} matchSuffix
+   * @param {string | number} [cursor]
    */
-  async scan(matchSuffix: string, cursor: string | number = 0) {
+  async scan(matchSuffix, cursor = 0) {
     return redis.scan(cursor, {
       match: withScanPattern(CACHE_NS, matchSuffix),
       count: 100,
@@ -70,8 +99,12 @@ export const cache = {
  * Build a sliding-window rate limiter scoped to the BSK app + env.
  * `name` is the bucket label (e.g. "login", "queue-pickup"); it's appended
  * after the bsk:{env}:ratelimit prefix and used to namespace the bucket.
+ *
+ * @param {string} name
+ * @param {number} requests
+ * @param {number} windowSeconds
  */
-export function createRateLimiter(name: string, requests: number, windowSeconds: number) {
+export function createRateLimiter(name, requests, windowSeconds) {
   if (!/^[a-z0-9-]+$/.test(name)) {
     throw new Error(`Rate-limiter name must be kebab-case alphanumerics: ${name}`);
   }
@@ -87,8 +120,10 @@ export function createRateLimiter(name: string, requests: number, windowSeconds:
  * QStash signature verifier. Wraps the current + next signing keys so rotation
  * doesn't require code changes. Returns null when signing keys are not configured
  * (preview / dev environments without QStash provisioned).
+ *
+ * @returns {Receiver | null}
  */
-export function getQStashReceiver(): Receiver | null {
+export function getQStashReceiver() {
   if (!serverEnv.QSTASH_CURRENT_SIGNING_KEY || !serverEnv.QSTASH_NEXT_SIGNING_KEY) {
     return null;
   }
diff --git a/lib/utils.js b/lib/utils.js
new file mode 100644
index 0000000..3b6fc47
--- /dev/null
+++ b/lib/utils.js
@@ -0,0 +1,7 @@
+import { clsx } from "clsx";
+import { twMerge } from "tailwind-merge";
+
+/** @param {import("clsx").ClassValue[]} inputs */
+export function cn(...inputs) {
+  return twMerge(clsx(inputs));
+}
diff --git a/lib/utils.ts b/lib/utils.ts
deleted file mode 100644
index a5ef193..0000000
--- a/lib/utils.ts
+++ /dev/null
@@ -1,6 +0,0 @@
-import { clsx, type ClassValue } from "clsx";
-import { twMerge } from "tailwind-merge";
-
-export function cn(...inputs: ClassValue[]) {
-  return twMerge(clsx(inputs));
-}
diff --git a/next.config.ts b/next.config.mjs
similarity index 51%
rename from next.config.ts
rename to next.config.mjs
index b0eb03c..9423db0 100644
--- a/next.config.ts
+++ b/next.config.mjs
@@ -1,9 +1,9 @@
-import type { NextConfig } from "next";
 import createNextIntlPlugin from "next-intl/plugin";
 
-const withNextIntl = createNextIntlPlugin("./i18n/request.ts");
+const withNextIntl = createNextIntlPlugin("./i18n/request.js");
 
-const nextConfig: NextConfig = {
+/** @type {import('next').NextConfig} */
+const nextConfig = {
   reactStrictMode: true,
   typedRoutes: true,
 };
diff --git a/package-lock.json b/package-lock.json
index cc622b1..1f24f5e 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -46,11 +46,11 @@
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       "resolved": "https://registry.npmjs.org/argparse/-/argparse-2.0.1.tgz",
@@ -6830,6 +6421,16 @@
         "node": ">=18"
       }
     },
+    "node_modules/comment-parser": {
+      "version": "1.4.8",
+      "resolved": "https://registry.npmjs.org/comment-parser/-/comment-parser-1.4.8.tgz",
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+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">= 12.0.0"
+      }
+    },
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       "version": "0.0.1",
       "resolved": "https://registry.npmjs.org/concat-map/-/concat-map-0.0.1.tgz",
@@ -7465,48 +7066,6 @@
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-      "license": "MIT",
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-        "@esbuild/android-x64": "0.28.2",
-        "@esbuild/darwin-arm64": "0.28.2",
-        "@esbuild/darwin-x64": "0.28.2",
-        "@esbuild/freebsd-arm64": "0.28.2",
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-        "@esbuild/linux-riscv64": "0.28.2",
-        "@esbuild/linux-s390x": "0.28.2",
-        "@esbuild/linux-x64": "0.28.2",
-        "@esbuild/netbsd-arm64": "0.28.2",
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-        "@esbuild/openbsd-arm64": "0.28.2",
-        "@esbuild/openbsd-x64": "0.28.2",
-        "@esbuild/openharmony-arm64": "0.28.2",
-        "@esbuild/sunos-x64": "0.28.2",
-        "@esbuild/win32-arm64": "0.28.2",
-        "@esbuild/win32-ia32": "0.28.2",
-        "@esbuild/win32-x64": "0.28.2"
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       "resolved": "https://registry.npmjs.org/escalade/-/escalade-3.2.0.tgz",
@@ -7775,6 +7334,92 @@
         "ms": "^2.1.1"
       }
     },
+    "node_modules/eslint-plugin-jsdoc": {
+      "version": "64.2.0",
+      "resolved": "https://registry.npmjs.org/eslint-plugin-jsdoc/-/eslint-plugin-jsdoc-64.2.0.tgz",
+      "integrity": "sha512-z3zGmJoPhOdKnxzQ3R+8MZeJjW8vrRW8r7sYp/ErBp8K9+05RIa6vWXtbEGr7D1obBHk64LdKyLHoMLSzHFINA==",
+      "dev": true,
+      "license": "BSD-3-Clause",
+      "dependencies": {
+        "@es-joy/jsdoccomment": "~0.95.0",
+        "@es-joy/resolve.exports": "1.2.0",
+        "are-docs-informative": "^0.1.1",
+        "comment-parser": "1.4.8",
+        "debug": "^4.4.3",
+        "escape-string-regexp": "^5.0.0",
+        "espree": "^11.2.0",
+        "esquery": "^1.7.0",
+        "html-entities": "^2.6.0",
+        "object-deep-merge": "^2.0.1",
+        "parse-imports-exports": "^0.2.4",
+        "semver": "^7.8.5",
+        "spdx-expression-parse": "^5.0.0",
+        "to-valid-identifier": "^1.0.0"
+      },
+      "engines": {
+        "node": "^22.22.2 || >=24.15.0"
+      },
+      "peerDependencies": {
+        "eslint": "^7.0.0 || ^8.0.0 || ^9.0.0 || ^10.0.0"
+      }
+    },
+    "node_modules/eslint-plugin-jsdoc/node_modules/escape-string-regexp": {
+      "version": "5.0.0",
+      "resolved": "https://registry.npmjs.org/escape-string-regexp/-/escape-string-regexp-5.0.0.tgz",
+      "integrity": "sha512-/veY75JbMK4j1yjvuUxuVsiS/hr/4iHs9FTT6cgTexxdE0Ly/glccBAkloH/DofkjRbZU3bnoj38mOmhkZ0lHw==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=12"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/sindresorhus"
+      }
+    },
+    "node_modules/eslint-plugin-jsdoc/node_modules/eslint-visitor-keys": {
+      "version": "5.0.1",
+      "resolved": "https://registry.npmjs.org/eslint-visitor-keys/-/eslint-visitor-keys-5.0.1.tgz",
+      "integrity": "sha512-tD40eHxA35h0PEIZNeIjkHoDR4YjjJp34biM0mDvplBe//mB+IHCqHDGV7pxF+7MklTvighcCPPZC7ynWyjdTA==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "engines": {
+        "node": "^20.19.0 || ^22.13.0 || >=24"
+      },
+      "funding": {
+        "url": "https://opencollective.com/eslint"
+      }
+    },
+    "node_modules/eslint-plugin-jsdoc/node_modules/espree": {
+      "version": "11.2.0",
+      "resolved": "https://registry.npmjs.org/espree/-/espree-11.2.0.tgz",
+      "integrity": "sha512-7p3DrVEIopW1B1avAGLuCSh1jubc01H2JHc8B4qqGblmg5gI9yumBgACjWo4JlIc04ufug4xJ3SQI8HkS/Rgzw==",
+      "dev": true,
+      "license": "BSD-2-Clause",
+      "dependencies": {
+        "acorn": "^8.16.0",
+        "acorn-jsx": "^5.3.2",
+        "eslint-visitor-keys": "^5.0.1"
+      },
+      "engines": {
+        "node": "^20.19.0 || ^22.13.0 || >=24"
+      },
+      "funding": {
+        "url": "https://opencollective.com/eslint"
+      }
+    },
+    "node_modules/eslint-plugin-jsdoc/node_modules/semver": {
+      "version": "7.8.5",
+      "resolved": "https://registry.npmjs.org/semver/-/semver-7.8.5.tgz",
+      "integrity": "sha512-Y7/KDsb8LjooZpwaqGyulO6DQlksgCncchHGk+sZIY4SBvUocMBEFH5Ur1fI4dV+Jvl0w6cjvucaIi40puRioA==",
+      "dev": true,
+      "license": "ISC",
+      "bin": {
+        "semver": "bin/semver.js"
+      },
+      "engines": {
+        "node": ">=10"
+      }
+    },
     "node_modules/eslint-plugin-jsx-a11y": {
       "version": "6.10.2",
       "resolved": "https://registry.npmjs.org/eslint-plugin-jsx-a11y/-/eslint-plugin-jsx-a11y-6.10.2.tgz",
@@ -8061,23 +7706,6 @@
       "dev": true,
       "license": "MIT"
     },
-    "node_modules/fast-uri": {
-      "version": "3.1.5",
-      "resolved": "https://registry.npmjs.org/fast-uri/-/fast-uri-3.1.5.tgz",
-      "integrity": "sha512-gHwA1O9LDIcKunMKhObS/HimwtehO1nPUECKAu5TpKgaO19fcWEl4bliWe1jWxVFvIXztJjjQ4L8XQ1EU9f7Jw==",
-      "extraneous": true,
-      "funding": [
-        {
-          "type": "github",
-          "url": "https://github.com/sponsors/fastify"
-        },
-        {
-          "type": "opencollective",
-          "url": "https://opencollective.com/fastify"
-        }
-      ],
-      "license": "BSD-3-Clause"
-    },
     "node_modules/fastq": {
       "version": "1.20.1",
       "resolved": "https://registry.npmjs.org/fastq/-/fastq-1.20.1.tgz",
@@ -8537,6 +8165,23 @@
       "integrity": "sha512-LgOWAkrN0rFaQpfdWBQlv/VhkOxb5AsBjk6NQVx4yEzWS923T07X0M1Y0VNko2H52HeSpZrZNNMJ0aFqsdVzQg==",
       "license": "ISC"
     },
+    "node_modules/html-entities": {
+      "version": "2.6.0",
+      "resolved": "https://registry.npmjs.org/html-entities/-/html-entities-2.6.0.tgz",
+      "integrity": "sha512-kig+rMn/QOVRvr7c86gQ8lWXq+Hkv6CbAH1hLu+RG338StTpE8Z0b44SDVaqVu7HGKf27frdmUYEs9hTUX/cLQ==",
+      "dev": true,
+      "funding": [
+        {
+          "type": "github",
+          "url": "https://github.com/sponsors/mdevils"
+        },
+        {
+          "type": "patreon",
+          "url": "https://patreon.com/mdevils"
+        }
+      ],
+      "license": "MIT"
+    },
     "node_modules/html-escaper": {
       "version": "2.0.2",
       "resolved": "https://registry.npmjs.org/html-escaper/-/html-escaper-2.0.2.tgz",
@@ -9242,6 +8887,19 @@
         "js-yaml": "bin/js-yaml.mjs"
       }
     },
+    "node_modules/jsdoc-type-pratt-parser": {
+      "version": "9.1.1",
+      "resolved": "https://registry.npmjs.org/jsdoc-type-pratt-parser/-/jsdoc-type-pratt-parser-9.1.1.tgz",
+      "integrity": "sha512-kojSbQb9iQM2bk2PmHiKa3reG0U4v2gN9U8D8+eCQq+4KM5ZXBUyBVeF8KmR0RiwqyrW4+uVWYWTOLnpsavnkw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/estree": "^1.0.9"
+      },
+      "engines": {
+        "node": "^22.22.2 || >=24.15.0"
+      }
+    },
     "node_modules/jsesc": {
       "version": "3.1.0",
       "resolved": "https://registry.npmjs.org/jsesc/-/jsesc-3.1.0.tgz",
@@ -9262,13 +8920,6 @@
       "dev": true,
       "license": "MIT"
     },
-    "node_modules/json-schema-traverse": {
-      "version": "1.0.0",
-      "resolved": "https://registry.npmjs.org/json-schema-traverse/-/json-schema-traverse-1.0.0.tgz",
-      "integrity": "sha512-NM8/P9n3XjXhIZn1lLhkFaACTOURQXjWhV4BA/RnOv8xvgqtqpAX9IO4mRQxSx1Rlo4tqzeqb0sOlruaOy3dug==",
-      "extraneous": true,
-      "license": "MIT"
-    },
     "node_modules/json-stable-stringify-without-jsonify": {
       "version": "1.0.1",
       "resolved": "https://registry.npmjs.org/json-stable-stringify-without-jsonify/-/json-stable-stringify-without-jsonify-1.0.1.tgz",
@@ -10068,6 +9719,13 @@
         "node": ">=0.10.0"
       }
     },
+    "node_modules/object-deep-merge": {
+      "version": "2.0.1",
+      "resolved": "https://registry.npmjs.org/object-deep-merge/-/object-deep-merge-2.0.1.tgz",
+      "integrity": "sha512-aKttDKcU3pyZqKcCkDhsMn70WmZFG2JGDQLP9EcLyTSIFQRCPWLAmBZRLJnrVUrhPG1jETEEbfdgbNtJf1LyMg==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/object-inspect": {
       "version": "1.13.4",
       "resolved": "https://registry.npmjs.org/object-inspect/-/object-inspect-1.13.4.tgz",
@@ -10283,6 +9941,23 @@
         "node": ">=6"
       }
     },
+    "node_modules/parse-imports-exports": {
+      "version": "0.2.4",
+      "resolved": "https://registry.npmjs.org/parse-imports-exports/-/parse-imports-exports-0.2.4.tgz",
+      "integrity": "sha512-4s6vd6dx1AotCx/RCI2m7t7GCh5bDRUtGNvRfHSP2wbBQdMi67pPe7mtzmgwcaQ8VKK/6IB7Glfyu3qdZJPybQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "parse-statements": "1.0.11"
+      }
+    },
+    "node_modules/parse-statements": {
+      "version": "1.0.11",
+      "resolved": "https://registry.npmjs.org/parse-statements/-/parse-statements-1.0.11.tgz",
+      "integrity": "sha512-HlsyYdMBnbPQ9Jr/VgJ1YF4scnldvJpJxCVx6KgqPL4dxppsWrJHCIIxQXMJrqGnsRkNPATbeMJ8Yxu7JMsYcA==",
+      "dev": true,
+      "license": "MIT"
+    },
     "node_modules/parse-svg-path": {
       "version": "0.1.2",
       "resolved": "https://registry.npmjs.org/parse-svg-path/-/parse-svg-path-0.1.2.tgz",
@@ -10917,6 +10592,19 @@
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       "license": "MIT"
     },
+    "node_modules/reserved-identifiers": {
+      "version": "1.2.0",
+      "resolved": "https://registry.npmjs.org/reserved-identifiers/-/reserved-identifiers-1.2.0.tgz",
+      "integrity": "sha512-yE7KUfFvaBFzGPs5H3Ops1RevfUEsDc5Iz65rOwWg4lE8HJSYtle77uul3+573457oHvBKuHYDl/xqUkKpEEdw==",
+      "dev": true,
+      "license": "MIT",
+      "engines": {
+        "node": ">=18"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/sindresorhus"
+      }
+    },
     "node_modules/resolve": {
       "version": "2.0.0-next.7",
       "resolved": "https://registry.npmjs.org/resolve/-/resolve-2.0.0-next.7.tgz",
@@ -11369,6 +11057,31 @@
         "node": ">=0.10.0"
       }
     },
+    "node_modules/spdx-exceptions": {
+      "version": "2.5.0",
+      "resolved": "https://registry.npmjs.org/spdx-exceptions/-/spdx-exceptions-2.5.0.tgz",
+      "integrity": "sha512-PiU42r+xO4UbUS1buo3LPJkjlO7430Xn5SVAhdpzzsPHsjbYVflnnFdATgabnLude+Cqu25p6N+g2lw/PFsa4w==",
+      "dev": true,
+      "license": "CC-BY-3.0"
+    },
+    "node_modules/spdx-expression-parse": {
+      "version": "5.0.0",
+      "resolved": "https://registry.npmjs.org/spdx-expression-parse/-/spdx-expression-parse-5.0.0.tgz",
+      "integrity": "sha512-vngmw3Rgn+o2arXNbnZaj5UtOEBuWBfvaI+Wc8GFfykIhA5/vdK9/Sp/XkLv63dykz2rxKDvKEHupF5P0FORcQ==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "spdx-exceptions": "^2.1.0",
+        "spdx-license-ids": "^3.0.0"
+      }
+    },
+    "node_modules/spdx-license-ids": {
+      "version": "3.0.23",
+      "resolved": "https://registry.npmjs.org/spdx-license-ids/-/spdx-license-ids-3.0.23.tgz",
+      "integrity": "sha512-CWLcCCH7VLu13TgOH+r8p1O/Znwhqv/dbb6lqWy67G+pT1kHmeD/+V36AVb/vq8QMIQwVShJ6Ssl5FPh0fuSdw==",
+      "dev": true,
+      "license": "CC0-1.0"
+    },
     "node_modules/stable-hash": {
       "version": "0.0.5",
       "resolved": "https://registry.npmjs.org/stable-hash/-/stable-hash-0.0.5.tgz",
@@ -11736,6 +11449,23 @@
         "node": ">=8.0"
       }
     },
+    "node_modules/to-valid-identifier": {
+      "version": "1.0.0",
+      "resolved": "https://registry.npmjs.org/to-valid-identifier/-/to-valid-identifier-1.0.0.tgz",
+      "integrity": "sha512-41wJyvKep3yT2tyPqX/4blcfybknGB4D+oETKLs7Q76UiPqRpUJK3hr1nxelyYO0PHKVzJwlu0aCeEAsGI6rpw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@sindresorhus/base62": "^1.0.0",
+        "reserved-identifiers": "^1.0.0"
+      },
+      "engines": {
+        "node": ">=20"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/sindresorhus"
+      }
+    },
     "node_modules/ts-api-utils": {
       "version": "2.5.0",
       "resolved": "https://registry.npmjs.org/ts-api-utils/-/ts-api-utils-2.5.0.tgz",
@@ -11781,40 +11511,6 @@
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       "license": "0BSD"
     },
-    "node_modules/tsx": {
-      "version": "4.23.12",
-      "resolved": "https://registry.npmjs.org/tsx/-/tsx-4.23.12.tgz",
-      "integrity": "sha512-FDf4L4sYzKtzWYhU/Xm0AQFdTjdIxNo9ElTf2mxXM6k8YMHXzYUe4yODVaXP4V9uMFbVg8c0qyBccK2OOxb45Q==",
-      "dev": true,
-      "license": "MIT",
-      "dependencies": {
-        "esbuild": "~0.28.0"
-      },
-      "bin": {
-        "tsx": "dist/cli.mjs"
-      },
-      "engines": {
-        "node": ">=18.0.0"
-      },
-      "optionalDependencies": {
-        "fsevents": "~2.3.3"
-      }
-    },
-    "node_modules/tsx/node_modules/fsevents": {
-      "version": "2.3.3",
-      "resolved": "https://registry.npmjs.org/fsevents/-/fsevents-2.3.3.tgz",
-      "integrity": "sha512-5xoDfX+fL7faATnagmWPpbFtwh/R77WmMMqqHGS65C3vvB0YHrgF+B1YmZ3441tMj5n63k0212XNoJwzlhffQw==",
-      "dev": true,
-      "hasInstallScript": true,
-      "license": "MIT",
-      "optional": true,
-      "os": [
-        "darwin"
-      ],
-      "engines": {
-        "node": "^8.16.0 || ^10.6.0 || >=11.0.0"
-      }
-    },
     "node_modules/type-check": {
       "version": "0.4.0",
       "resolved": "https://registry.npmjs.org/type-check/-/type-check-0.4.0.tgz",
diff --git a/package.json b/package.json
index 4ec602d..088c9c9 100644
--- a/package.json
+++ b/package.json
@@ -10,17 +10,17 @@
     "build": "next build",
     "start": "next start",
     "lint": "eslint .",
-    "typecheck": "tsc --noEmit",
+    "typecheck": "tsc -p jsconfig.json",
     "format": "prettier --write .",
     "format:check": "prettier --check .",
     "test": "vitest run",
     "test:watch": "vitest",
     "test:coverage": "vitest run --coverage",
     "test:e2e": "playwright test",
-    "db:preflight": "tsx scripts/preflight-supabase.ts",
+    "db:preflight": "node scripts/preflight-supabase.mjs",
     "db:push": "npm run db:preflight && supabase db push",
-    "db:gen-types": "supabase gen types typescript --schema bsk > types/supabase-bsk.ts",
-    "db:seed-geo": "tsx scripts/seed-geo.ts",
+    "db:gen-types": "supabase gen types typescript --schema bsk > types/supabase-bsk.d.ts",
+    "db:seed-geo": "node scripts/seed-geo.mjs",
     "check:no-secret-leak": "node scripts/check-no-secret-leak.mjs"
   },
   "dependencies": {
@@ -62,11 +62,11 @@
     "eslint": "^9.36.0",
     "eslint-config-next": "^16.2.6",
     "eslint-config-prettier": "^10.1.8",
+    "eslint-plugin-jsdoc": "^64.2.0",
     "postcss": "^8.5.18",
     "prettier": "^3.8.3",
     "prettier-plugin-tailwindcss": "^0.8.0",
     "tailwindcss": "^4.3.0",
-    "tsx": "^4.22.3",
     "typescript": "^5.9.2",
     "vitest": "^4.1.10"
   },
diff --git a/playwright.config.ts b/playwright.config.js
similarity index 100%
rename from playwright.config.ts
rename to playwright.config.js
diff --git a/proxy.ts b/proxy.js
similarity index 94%
rename from proxy.ts
rename to proxy.js
index 85094c4..cc0e773 100644
--- a/proxy.ts
+++ b/proxy.js
@@ -1,5 +1,5 @@
 import createMiddleware from "next-intl/middleware";
-import { NextResponse, type NextRequest } from "next/server";
+import { NextResponse } from "next/server";
 import { routing } from "@/i18n/routing";
 import { updateSupabaseSession, PROTECTED_PATH_PREFIXES } from "@/lib/supabase/session";
 import { copyCookies } from "@/lib/proxy/copy-cookies";
@@ -18,7 +18,11 @@ const handleI18nRouting = createMiddleware(routing);
  * Strips the leading locale segment before comparing so "/vi/dashboard" and
  * "/en/dashboard" both match "/dashboard".
  */
-function isProtectedPath(pathname: string): boolean {
+/**
+ * @param {string} pathname
+ * @returns {boolean}
+ */
+function isProtectedPath(pathname) {
   // Remove a leading locale segment if present (e.g. "/vi" or "/en").
   const localeSegmentRe = new RegExp(`^\\/(${routing.locales.join("|")})(\\/.*)?(\\?.*)?$`);
   const match = localeSegmentRe.exec(pathname);
@@ -51,7 +55,11 @@ function isProtectedPath(pathname: string): boolean {
  * NOTE: No `export const runtime = 'edge'` — proxy runs on the Node.js runtime
  * in Next.js 16+. Supabase SSR is not certified for the Edge runtime.
  */
-export default async function proxy(request: NextRequest): Promise<NextResponse> {
+/**
+ * @param {import("next/server").NextRequest} request
+ * @returns {Promise<NextResponse>}
+ */
+export default async function proxy(request) {
   // ── Step 1: Supabase session refresh ─────────────────────────────────────
   const { response: supabaseResponse, user } = await updateSupabaseSession(request);
 
diff --git a/scripts/preflight-supabase.ts b/scripts/preflight-supabase.mjs
similarity index 86%
rename from scripts/preflight-supabase.ts
rename to scripts/preflight-supabase.mjs
index f7e8b48..dce01c3 100644
--- a/scripts/preflight-supabase.ts
+++ b/scripts/preflight-supabase.mjs
@@ -1,4 +1,4 @@
-#!/usr/bin/env tsx
+#!/usr/bin/env node
 /**
  * Preflight guard for `supabase db push` against the shared project.
  *
@@ -9,7 +9,7 @@
  * currently-linked Supabase project ref matches BSK's allow-list.
  *
  * Wire it in package.json:
- *   "db:push": "tsx scripts/preflight-supabase.ts && supabase db push"
+ *   "db:push": "node scripts/preflight-supabase.mjs && supabase db push"
  *
  * The allow-list is intentionally checked into the repo: it's not secret,
  * and a PR diff is the right place to notice "wait, why did the ref change?"
@@ -20,11 +20,13 @@ import { resolve } from "node:path";
 
 // BSK is only ever linked to these project refs. Add new ones via PR.
 // Source of truth: Supabase dashboard → Project Settings → General → Reference ID.
-const ALLOWED_PROJECT_REFS: ReadonlyArray<string> = [
+/** @type {ReadonlyArray<string>} */
+const ALLOWED_PROJECT_REFS = [
   // "abcdefghijklmnopqrst", // example: tiennm99's personal shared project
 ];
 
-function readLinkedRef(): string | null {
+/** @returns {string | null} */
+function readLinkedRef() {
   // `supabase link` writes the project ref to supabase/.temp/project-ref.
   try {
     const path = resolve(process.cwd(), "supabase/.temp/project-ref");
@@ -34,7 +36,11 @@ function readLinkedRef(): string | null {
   }
 }
 
-function die(msg: string): never {
+/**
+ * @param {string} msg
+ * @returns {never}
+ */
+function die(msg) {
   process.stderr.write(`\n[preflight-supabase] ${msg}\n\n`);
   process.exit(1);
 }
@@ -50,7 +56,7 @@ if (!ref) {
 
 if (ALLOWED_PROJECT_REFS.length === 0) {
   die(
-    "ALLOWED_PROJECT_REFS is empty in scripts/preflight-supabase.ts.\n" +
+    "ALLOWED_PROJECT_REFS is empty in scripts/preflight-supabase.mjs.\n" +
       "Add your BSK Supabase project ref(s) to the allow-list before pushing migrations.",
   );
 }
@@ -63,7 +69,7 @@ if (!ALLOWED_PROJECT_REFS.includes(ref)) {
       `Pushing to the wrong project can require a project-wide PITR to recover —\n` +
       `which would wipe every other app's data too.\n\n` +
       `If "${ref}" is legitimately a new BSK project, add it to ALLOWED_PROJECT_REFS\n` +
-      `in scripts/preflight-supabase.ts via a PR, then re-run.`,
+      `in scripts/preflight-supabase.mjs via a PR, then re-run.`,
   );
 }
 
diff --git a/scripts/seed-geo.ts b/scripts/seed-geo.mjs
similarity index 83%
rename from scripts/seed-geo.ts
rename to scripts/seed-geo.mjs
index 970d415..37de440 100644
--- a/scripts/seed-geo.ts
+++ b/scripts/seed-geo.mjs
@@ -1,4 +1,4 @@
-#!/usr/bin/env tsx
+#!/usr/bin/env node
 /**
  * Seed Vietnamese geo lookup (bsk.provinces + bsk.wards).
  *
@@ -23,10 +23,14 @@ import { readFileSync } from "node:fs";
 import { resolve } from "node:path";
 import { createClient } from "@supabase/supabase-js";
 
-type Ward = { code: string; name: string };
-type Province = { code: string; name: string; wards: Ward[] };
+/** @typedef {{ code: string, name: string }} Ward */
+/** @typedef {{ code: string, name: string, wards: Ward[] }} Province */
 
-function die(msg: string): never {
+/**
+ * @param {string} msg
+ * @returns {never}
+ */
+function die(msg) {
   process.stderr.write(`\n[seed-geo] ${msg}\n\n`);
   process.exit(1);
 }
@@ -38,7 +42,8 @@ if (!url || !key) {
 }
 
 const dataPath = resolve(process.cwd(), "supabase/seed/vn-geo.json");
-let provinces: Province[];
+/** @type {Province[]} */
+let provinces;
 try {
   provinces = JSON.parse(readFileSync(dataPath, "utf8"));
 } catch {
@@ -54,14 +59,17 @@ if (!Array.isArray(provinces) || provinces.length === 0) {
 
 const supabase = createClient(url, key, { db: { schema: "bsk" }, auth: { persistSession: false } });
 
-async function upsertBatched<T>(
-  table: "provinces" | "wards",
-  rows: T[],
-  size = 500,
-): Promise<void> {
+/**
+ * @template T
+ * @param {"provinces" | "wards"} table
+ * @param {T[]} rows
+ * @param {number} [size]
+ * @returns {Promise<void>}
+ */
+async function upsertBatched(table, rows, size = 500) {
   for (let i = 0; i < rows.length; i += size) {
     const batch = rows.slice(i, i + size);
-    const { error } = await supabase.from(table).upsert(batch as never[]);
+    const { error } = await supabase.from(table).upsert(/** @type {never[]} */ (batch));
     if (error) die(`Upsert into ${table} failed at row ${i}: ${error.message}`);
     process.stdout.write(
       `[seed-geo] ${table}: ${Math.min(i + size, rows.length)}/${rows.length}\n`,
diff --git a/tests/e2e/auth-gate.spec.ts b/tests/e2e/auth-gate.spec.js
similarity index 100%
rename from tests/e2e/auth-gate.spec.ts
rename to tests/e2e/auth-gate.spec.js
diff --git a/tests/e2e/i18n-and-404.spec.ts b/tests/e2e/i18n-and-404.spec.js
similarity index 100%
rename from tests/e2e/i18n-and-404.spec.ts
rename to tests/e2e/i18n-and-404.spec.js
diff --git a/tests/e2e/sign-in-page.spec.ts b/tests/e2e/sign-in-page.spec.js
similarity index 100%
rename from tests/e2e/sign-in-page.spec.ts
rename to tests/e2e/sign-in-page.spec.js
diff --git a/tests/unit/checkup-schema.test.ts b/tests/unit/checkup-schema.test.js
similarity index 93%
rename from tests/unit/checkup-schema.test.ts
rename to tests/unit/checkup-schema.test.js
index aaa33fa..79f81d3 100644
--- a/tests/unit/checkup-schema.test.ts
+++ b/tests/unit/checkup-schema.test.js
@@ -53,7 +53,7 @@ describe("CheckupSaveSchema", () => {
       conclusion: "",
       notes: "",
       recheckDate: "",
-      status: "in_progress" as const,
+      status: /** @type {import("@/lib/checkups/checkup-schema").CheckupStatus} */ ("in_progress"),
     };
     const result = CheckupSaveSchema.safeParse(payload);
     expect(result.success).toBe(true);
@@ -89,7 +89,7 @@ describe("CheckupSaveSchema", () => {
       conclusion: "",
       notes: "",
       recheckDate: "2026-08-10",
-      status: "done" as const,
+      status: /** @type {import("@/lib/checkups/checkup-schema").CheckupStatus} */ ("done"),
     };
     const result = CheckupSaveSchema.safeParse(payload);
     expect(result.success).toBe(true);
@@ -107,7 +107,7 @@ describe("CheckupSaveSchema", () => {
       conclusion: "",
       notes: "",
       recheckDate: "invalid-date",
-      status: "done" as const,
+      status: /** @type {import("@/lib/checkups/checkup-schema").CheckupStatus} */ ("done"),
     };
     const result = CheckupSaveSchema.safeParse(payload);
     expect(result.success).toBe(false);
@@ -125,7 +125,7 @@ describe("CheckupSaveSchema", () => {
       conclusion: "Rest",
       notes: "Monitor",
       recheckDate: "",
-      status: "done" as const,
+      status: /** @type {import("@/lib/checkups/checkup-schema").CheckupStatus} */ ("done"),
     };
     const result = CheckupSaveSchema.safeParse(payload);
     expect(result.success).toBe(true);
diff --git a/tests/unit/customer-schema.test.ts b/tests/unit/customer-schema.test.js
similarity index 97%
rename from tests/unit/customer-schema.test.ts
rename to tests/unit/customer-schema.test.js
index f09cdbe..cbbccd5 100644
--- a/tests/unit/customer-schema.test.ts
+++ b/tests/unit/customer-schema.test.js
@@ -43,7 +43,7 @@ describe("CustomerSchema", () => {
     const payload = {
       ...validBase,
       dob: "1990-05-15",
-      gender: "male" as const,
+      gender: /** @type {import("@/lib/customers/customer-schema").Gender} */ ("male"),
       phone: "0912345678",
       cccd: "012345678901",
       provinceCode: "079",
diff --git a/tests/unit/medicine-schema.test.ts b/tests/unit/medicine-schema.test.js
similarity index 100%
rename from tests/unit/medicine-schema.test.ts
rename to tests/unit/medicine-schema.test.js
diff --git a/tests/unit/mocks/server-only.ts b/tests/unit/mocks/server-only.js
similarity index 100%
rename from tests/unit/mocks/server-only.ts
rename to tests/unit/mocks/server-only.js
diff --git a/tests/unit/patient-info.test.ts b/tests/unit/patient-info.test.js
similarity index 100%
rename from tests/unit/patient-info.test.ts
rename to tests/unit/patient-info.test.js
diff --git a/tests/unit/service-schema.test.ts b/tests/unit/service-schema.test.js
similarity index 100%
rename from tests/unit/service-schema.test.ts
rename to tests/unit/service-schema.test.js
diff --git a/tests/unit/template-schema.test.ts b/tests/unit/template-schema.test.js
similarity index 100%
rename from tests/unit/template-schema.test.ts
rename to tests/unit/template-schema.test.js
diff --git a/tests/unit/totals.test.ts b/tests/unit/totals.test.js
similarity index 100%
rename from tests/unit/totals.test.ts
rename to tests/unit/totals.test.js
diff --git a/types/supabase-bsk.ts b/types/supabase-bsk.d.ts
similarity index 100%
rename from types/supabase-bsk.ts
rename to types/supabase-bsk.d.ts
diff --git a/vitest.config.ts b/vitest.config.js
similarity index 71%
rename from vitest.config.ts
rename to vitest.config.js
index 207e296..bd2b32d 100644
--- a/vitest.config.ts
+++ b/vitest.config.js
@@ -4,18 +4,18 @@ import path from "path";
 export default defineConfig({
   test: {
     environment: "node",
-    include: ["tests/unit/**/*.test.ts"],
+    include: ["tests/unit/**/*.test.js"],
     coverage: {
       provider: "v8",
       reporter: ["text", "json", "html"],
-      include: ["lib/**/*.ts"],
-      exclude: ["lib/**/*.d.ts", "lib/**/*.config.ts"],
+      include: ["lib/**/*.js"],
+      exclude: ["lib/**/*.d.ts", "lib/**/*.config.js"],
     },
   },
   resolve: {
     alias: {
       "@": path.resolve(__dirname, "."),
-      "server-only": path.resolve(__dirname, "tests/unit/mocks/server-only.ts"),
+      "server-only": path.resolve(__dirname, "tests/unit/mocks/server-only.js"),
     },
   },
 });