feat: add Cron Triggers support to module framework

- modules may declare crons: [{ schedule, name, handler }]
- handler signature (event, { db, sql, env }) matches init context
- scheduled() export in src/index.js dispatches to matching handlers with fan-out and per-handler error isolation
- registry validates cron entries and collects into registry.crons
- wrangler.toml [triggers] crons must still be populated manually by module author

src/modules/cron-dispatcher.js

@@ -0,0 +1,45 @@
+/**
+ * @file cron-dispatcher — dispatches a Cloudflare scheduled event to all
+ * matching module cron handlers.
+ *
+ * Design:
+ *  - Iterates registry.crons, filters by event.cron === entry.schedule.
+ *  - Wraps each handler invocation in try/catch so one failure cannot block
+ *    others (equivalent to Promise.allSettled fan-out via ctx.waitUntil).
+ *  - ctx.waitUntil is fire-and-forget from Workers' perspective; we wrap in
+ *    an async IIFE so errors are caught and logged rather than silently lost.
+ */
+
+import { createSqlStore } from "../db/create-sql-store.js";
+import { createStore } from "../db/create-store.js";
+
+/**
+ * @param {any} event — Cloudflare ScheduledEvent (has .cron string).
+ * @param {any} env
+ * @param {{ waitUntil: (p: Promise<any>) => void }} ctx
+ * @param {import("./registry.js").Registry} registry
+ */
+export function dispatchScheduled(event, env, ctx, registry) {
+  const matching = registry.crons.filter((entry) => entry.schedule === event.cron);
+
+  for (const entry of matching) {
+    const handlerCtx = {
+      db: createStore(entry.module.name, env),
+      sql: createSqlStore(entry.module.name, env),
+      env,
+    };
+
+    ctx.waitUntil(
+      (async () => {
+        try {
+          await entry.handler(event, handlerCtx);
+        } catch (err) {
+          console.error(
+            `[cron] handler "${entry.name}" (module "${entry.module.name}", schedule "${entry.schedule}") failed:`,
+            err,
+          );
+        }
+      })(),
+    );
+  }
+}

src/modules/validate-cron.js

@@ -0,0 +1,66 @@
+/**
+ * @file validate-cron — validates module-registered cron entries.
+ *
+ * Cron entry contract:
+ *   - name: ^[a-z0-9_-]{1,32}$ — unique within the module (checked by registry)
+ *   - schedule: non-empty string matching a cron-ish pattern
+ *     (5 or 6 fields separated by spaces, e.g. "0 1 * * *")
+ *   - handler: function
+ *
+ * All errors include module name + cron name for debuggability.
+ */
+
+export const CRON_NAME_RE = /^[a-z0-9_-]{1,32}$/;
+
+/**
+ * Very loose cron expression check: 5 or 6 space-separated tokens.
+ * Cloudflare Workers validates the real expression at deploy time;
+ * we just catch obvious mistakes (empty string, random garbage).
+ */
+export const CRON_SCHEDULE_RE = /^\S+(\s+\S+){4,5}$/;
+
+/**
+ * @typedef {object} ModuleCron
+ * @property {string} name — unique identifier within the module.
+ * @property {string} schedule — cron expression, e.g. "0 1 * * *".
+ * @property {(event: any, ctx: { db: any, sql: any, env: any }) => Promise<void>|void} handler
+ */
+
+/**
+ * Throws on any contract violation. Called once per cron entry at registry build.
+ *
+ * @param {any} cron
+ * @param {string} moduleName — for error messages.
+ */
+export function validateCron(cron, moduleName) {
+  const prefix = `module "${moduleName}" cron`;
+
+  if (!cron || typeof cron !== "object") {
+    throw new Error(`${prefix}: cron entry is not an object`);
+  }
+
+  // name
+  if (typeof cron.name !== "string") {
+    throw new Error(`${prefix}: name must be a string`);
+  }
+  if (!CRON_NAME_RE.test(cron.name)) {
+    throw new Error(
+      `${prefix} "${cron.name}": name must match ${CRON_NAME_RE} (lowercase letters, digits, underscore, hyphen; 1–32 chars)`,
+    );
+  }
+
+  // schedule
+  if (typeof cron.schedule !== "string" || cron.schedule.trim().length === 0) {
+    throw new Error(`${prefix} "${cron.name}": schedule must be a non-empty string`);
+  }
+  if (!CRON_SCHEDULE_RE.test(cron.schedule.trim())) {
+    throw new Error(
+      `${prefix} "${cron.name}": schedule must be a valid cron expression (5 or 6 space-separated fields), got "${cron.schedule}"`,
+    );
+  }
+
+  // handler
+  if (typeof cron.handler !== "function") {
+    throw new Error(`${prefix} "${cron.name}": handler must be a function`);
+  }
+}