diff --git a/src/web-server/routes/cliproxy-auth-routes.ts b/src/web-server/routes/cliproxy-auth-routes.ts
index 17d761e2..af838c5b 100644
--- a/src/web-server/routes/cliproxy-auth-routes.ts
+++ b/src/web-server/routes/cliproxy-auth-routes.ts
@@ -50,29 +50,14 @@ import {
   validateAntigravityRiskAcknowledgement,
   isAntigravityResponsibilityBypassEnabled,
 } from '../../cliproxy/antigravity-responsibility';
+import { createRouteErrorHelpers } from './route-helpers';
 
 const router = Router();
 
 // Valid providers list - derived from canonical CLIPROXY_PROFILES
 const validProviders: CLIProxyProvider[] = [...CLIPROXY_PROFILES];
 
-function logRouteError(context: string, error: unknown): void {
-  if (error instanceof Error) {
-    console.error(`[cliproxy-auth-routes] ${context}: ${error.message}`);
-    return;
-  }
-  console.error(`[cliproxy-auth-routes] ${context}: unknown error`);
-}
-
-function respondInternalError(
-  res: Response,
-  error: unknown,
-  fallbackMessage: string,
-  statusCode = 500
-): void {
-  logRouteError(fallbackMessage, error);
-  res.status(statusCode).json({ error: fallbackMessage });
-}
+const { respondInternalError } = createRouteErrorHelpers('cliproxy-auth-routes');
 
 function parseKiroMethod(raw: unknown): { method: KiroAuthMethod; invalid: boolean } {
   if (raw === undefined || raw === null) {
diff --git a/src/web-server/routes/cliproxy-stats-routes.ts b/src/web-server/routes/cliproxy-stats-routes.ts
index 99bfb23b..4b082730 100644
--- a/src/web-server/routes/cliproxy-stats-routes.ts
+++ b/src/web-server/routes/cliproxy-stats-routes.ts
@@ -100,62 +100,21 @@ function isQuotaRouteRateLimited(req: Request, provider: string): boolean {
 }
 
 /**
- * Cache only stable failures; avoid pinning transient network failures (timeouts, 429s).
+ * Cache only stable failures; skip transient network errors (timeouts, 429s, 5xx).
+ * Generic across all quota result types.
  */
-function shouldCacheCodexQuotaResult(result: CodexQuotaResult): boolean {
+function shouldCacheQuotaResult(result: {
+  success: boolean;
+  needsReauth?: boolean;
+  isForbidden?: boolean;
+  error?: string;
+}): boolean {
   if (result.success) return true;
   if (result.needsReauth || result.isForbidden) return true;
-
   const msg = (result.error || '').toLowerCase();
   if (!msg) return false;
-  if (msg.includes('timeout')) return false;
-  if (msg.includes('rate limited')) return false;
-  if (msg.includes('api error: 5')) return false;
-  if (msg.includes('fetch failed')) return false;
-
-  return false;
-}
-
-function shouldCacheGeminiQuotaResult(result: GeminiCliQuotaResult): boolean {
-  if (result.success) return true;
-  if (result.needsReauth) return true;
-
-  const msg = (result.error || '').toLowerCase();
-  if (!msg) return false;
-  if (msg.includes('timeout')) return false;
-  if (msg.includes('rate limited')) return false;
-  if (msg.includes('api error: 5')) return false;
-  if (msg.includes('fetch failed')) return false;
-
-  return false;
-}
-
-function shouldCacheClaudeQuotaResult(result: ClaudeQuotaResult): boolean {
-  if (result.success) return true;
-  if (result.needsReauth) return true;
-
-  const msg = (result.error || '').toLowerCase();
-  if (!msg) return false;
-  if (msg.includes('timeout')) return false;
-  if (msg.includes('rate limited')) return false;
-  if (msg.includes('api error: 5')) return false;
-  if (msg.includes('fetch failed')) return false;
-
-  return false;
-}
-
-function shouldCacheGhcpQuotaResult(result: GhcpQuotaResult): boolean {
-  if (result.success) return true;
-  if (result.needsReauth) return true;
-
-  const msg = (result.error || '').toLowerCase();
-  if (!msg) return false;
-  if (msg.includes('timeout')) return false;
-  if (msg.includes('rate limited')) return false;
-  if (msg.includes('api error: 5')) return false;
-  if (msg.includes('fetch failed')) return false;
-
-  return false;
+  const transientPatterns = ['timeout', 'rate limited', 'api error: 5', 'fetch failed'];
+  return !transientPatterns.some((p) => msg.includes(p));
 }
 
 /** Get configured backend from config */
@@ -169,20 +128,21 @@ function getConfiguredBackend() {
 }
 
 /**
- * Extract status code and model from error log file (lightweight parsing)
- * Reads first 4KB for model, last 2KB for status code
+ * Extract status code and model from error log file (lightweight parsing).
+ * Reads first 4KB for model, last 2KB for status code. Async to avoid blocking event loop.
  */
 async function extractErrorLogMetadata(
   filePath: string
 ): Promise<{ statusCode?: number; model?: string }> {
+  let fh: fs.promises.FileHandle | null = null;
   try {
-    const fd = fs.openSync(filePath, 'r');
-    const stat = fs.fstatSync(fd);
+    fh = await fs.promises.open(filePath, 'r');
+    const stat = await fh.stat();
     const fileSize = stat.size;
 
     // Read first 4KB for model (in request body)
     const startBuffer = Buffer.alloc(Math.min(4096, fileSize));
-    fs.readSync(fd, startBuffer, 0, startBuffer.length, 0);
+    await fh.read(startBuffer, 0, startBuffer.length, 0);
     const startContent = startBuffer.toString('utf-8');
 
     // Extract model from request body JSON: "model":"gemini-3-flash-preview"
@@ -193,7 +153,7 @@ async function extractErrorLogMetadata(
     let statusCode: number | undefined;
     if (fileSize > 2048) {
       const endBuffer = Buffer.alloc(2048);
-      fs.readSync(fd, endBuffer, 0, 2048, fileSize - 2048);
+      await fh.read(endBuffer, 0, 2048, fileSize - 2048);
       const endContent = endBuffer.toString('utf-8');
       const statusMatch = endContent.match(/Status:\s*(\d{3})/);
       statusCode = statusMatch ? parseInt(statusMatch[1], 10) : undefined;
@@ -203,10 +163,11 @@ async function extractErrorLogMetadata(
       statusCode = statusMatch ? parseInt(statusMatch[1], 10) : undefined;
     }
 
-    fs.closeSync(fd);
     return { statusCode, model };
   } catch {
     return {};
+  } finally {
+    await fh?.close();
   }
 }
 
@@ -237,7 +198,8 @@ const handleStatsRequest = async (_req: Request, res: Response): Promise<void> =
 
     res.json(stats);
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 };
 
@@ -261,7 +223,8 @@ router.get('/status', async (_req: Request, res: Response): Promise<void> => {
     const running = await isCliproxyRunning();
     res.json({ running });
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -297,7 +260,8 @@ router.get('/proxy-status', async (_req: Request, res: Response): Promise<void>
       res.json(sessionStatus);
     }
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -311,7 +275,8 @@ router.post('/proxy-start', async (_req: Request, res: Response): Promise<void>
     const result = await ensureCliproxyService();
     res.json(result);
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -324,7 +289,8 @@ router.post('/proxy-stop', async (_req: Request, res: Response): Promise<void> =
     const result = await stopProxy();
     res.json(result);
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -338,7 +304,8 @@ router.get('/update-check', async (_req: Request, res: Response): Promise<void>
     const result = await checkCliproxyUpdate(backend);
     res.json(result);
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -370,7 +337,8 @@ router.get('/models', async (_req: Request, res: Response): Promise<void> => {
 
     res.json(modelsResponse);
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -417,7 +385,8 @@ router.get('/error-logs', async (_req: Request, res: Response): Promise<void> =>
 
     res.json({ files: filesWithMetadata });
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -456,7 +425,8 @@ router.get('/error-logs/:name', async (req: Request, res: Response): Promise<voi
 
     res.type('text/plain').send(content);
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -477,7 +447,8 @@ router.get('/config.yaml', async (_req: Request, res: Response): Promise<void> =
     const content = fs.readFileSync(configPath, 'utf8');
     res.type('text/yaml').send(content);
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -510,7 +481,8 @@ router.put('/config.yaml', async (req: Request, res: Response): Promise<void> =>
 
     res.json({ success: true, path: configPath });
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -544,7 +516,8 @@ router.get('/auth-files', async (_req: Request, res: Response): Promise<void> =>
 
     res.json({ files, directory: authDir });
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -580,7 +553,8 @@ router.get('/auth-files/download', async (req: Request, res: Response): Promise<
     res.setHeader('Content-Disposition', `attachment; filename="${name}"`);
     res.type('application/octet-stream').send(content);
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -667,7 +641,8 @@ router.put('/models/:provider', async (req: Request, res: Response): Promise<voi
 
     res.json({ success: true, provider, model: canonicalModel });
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -712,13 +687,14 @@ router.get('/quota/codex/:accountId', async (req: Request, res: Response): Promi
     const result = await fetchCodexQuota(accountId);
 
     // Cache successful and stable failure states; skip transient network failures.
-    if (shouldCacheCodexQuotaResult(result)) {
+    if (shouldCacheQuotaResult(result)) {
       setCachedQuota('codex', accountId, result);
     }
 
     res.json(result);
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -759,13 +735,14 @@ router.get('/quota/claude/:accountId', async (req: Request, res: Response): Prom
     const result = await fetchClaudeQuota(accountId);
 
     // Cache successful and stable failure states; skip transient network failures.
-    if (shouldCacheClaudeQuotaResult(result)) {
+    if (shouldCacheQuotaResult(result)) {
       setCachedQuota('claude', accountId, result);
     }
 
     res.json(result);
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -806,13 +783,14 @@ router.get('/quota/gemini/:accountId', async (req: Request, res: Response): Prom
     const result = await fetchGeminiCliQuota(accountId);
 
     // Cache successful and stable failure states; skip transient network failures.
-    if (shouldCacheGeminiQuotaResult(result)) {
+    if (shouldCacheQuotaResult(result)) {
       setCachedQuota('gemini', accountId, result);
     }
 
     res.json(result);
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -853,13 +831,14 @@ router.get('/quota/ghcp/:accountId', async (req: Request, res: Response): Promis
     const result = await fetchGhcpQuota(accountId);
 
     // Cache successful and stable failure states; skip transient network failures.
-    if (shouldCacheGhcpQuotaResult(result)) {
+    if (shouldCacheQuotaResult(result)) {
       setCachedQuota('ghcp', accountId, result);
     }
 
     res.json(result);
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -917,7 +896,8 @@ router.get('/quota/:provider/:accountId', async (req: Request, res: Response): P
 
     res.json(result);
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -940,7 +920,8 @@ router.get('/versions', async (_req: Request, res: Response): Promise<void> => {
       faultyRange: CLIPROXY_FAULTY_RANGE,
     });
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -1004,7 +985,8 @@ router.post('/install', async (req: Request, res: Response): Promise<void> => {
       message: `Successfully installed CLIProxy Plus v${version}`,
     });
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
@@ -1029,7 +1011,8 @@ router.post('/restart', async (_req: Request, res: Response): Promise<void> => {
       res.json({ success: false, error: startResult.error || 'Failed to start proxy' });
     }
   } catch (error) {
-    res.status(500).json({ error: (error as Error).message });
+    console.error(`[cliproxy-stats] ${(error as Error).message}`);
+    res.status(500).json({ error: 'Internal server error' });
   }
 });
 
diff --git a/src/web-server/routes/misc-routes.ts b/src/web-server/routes/misc-routes.ts
index fb3037c9..a3c7fbdc 100644
--- a/src/web-server/routes/misc-routes.ts
+++ b/src/web-server/routes/misc-routes.ts
@@ -10,6 +10,7 @@ import { expandPath } from '../../utils/helpers';
 import {
   loadOrCreateUnifiedConfig,
   saveUnifiedConfig,
+  mutateUnifiedConfig,
   getGlobalEnvConfig,
   getThinkingConfig,
   getConfigYamlPath,
@@ -218,28 +219,27 @@ router.get('/global-env', (_req: Request, res: Response): void => {
  * Updates the global_env section in config.yaml
  */
 router.put('/global-env', (req: Request, res: Response): void => {
-  try {
-    const { enabled, env } = req.body;
-    const config = loadOrCreateUnifiedConfig();
+  const { enabled, env } = req.body;
 
-    // Validate env is an object with string values
-    if (env !== undefined && typeof env === 'object' && env !== null) {
-      for (const [key, value] of Object.entries(env)) {
-        if (typeof value !== 'string') {
-          res.status(400).json({ error: `Invalid value for ${key}: must be a string` });
-          return;
-        }
+  // Validate env values before acquiring write lock
+  if (env !== undefined && typeof env === 'object' && env !== null) {
+    for (const [key, value] of Object.entries(env)) {
+      if (typeof value !== 'string') {
+        res.status(400).json({ error: `Invalid value for ${key}: must be a string` });
+        return;
       }
     }
+  }
 
-    // Update global_env section
-    config.global_env = {
-      enabled: enabled ?? config.global_env?.enabled ?? true,
-      env: env ?? config.global_env?.env ?? {},
-    };
-
-    saveUnifiedConfig(config);
-    res.json({ success: true, config: config.global_env });
+  try {
+    // Atomic read-modify-write — avoids race between load and save
+    const updated = mutateUnifiedConfig((config) => {
+      config.global_env = {
+        enabled: enabled ?? config.global_env?.enabled ?? true,
+        env: env ?? config.global_env?.env ?? {},
+      };
+    });
+    res.json({ success: true, config: updated.global_env });
   } catch (error) {
     res.status(500).json({ error: (error as Error).message });
   }
diff --git a/src/web-server/routes/profile-routes.ts b/src/web-server/routes/profile-routes.ts
index b450c77e..f8c87cab 100644
--- a/src/web-server/routes/profile-routes.ts
+++ b/src/web-server/routes/profile-routes.ts
@@ -13,9 +13,8 @@ import {
   updateApiProfileTarget,
 } from '../../api/services/profile-writer';
 import { apiProfileExists, listApiProfiles } from '../../api/services/profile-reader';
-import type { TargetType } from '../../targets/target-adapter';
 import { normalizeDroidProvider } from '../../targets/droid-provider';
-import { updateSettingsFile } from './route-helpers';
+import { updateSettingsFile, parseTarget } from './route-helpers';
 
 const router = Router();
 
@@ -23,23 +22,6 @@ function isDenylistError(message: string | undefined): boolean {
   return typeof message === 'string' && message.toLowerCase().includes('denylist');
 }
 
-export function parseTarget(rawTarget: unknown): TargetType | null {
-  if (rawTarget === undefined || rawTarget === null || rawTarget === '') {
-    return null;
-  }
-
-  if (typeof rawTarget !== 'string') {
-    return null;
-  }
-
-  const normalized = rawTarget.trim().toLowerCase();
-  if (normalized === 'claude' || normalized === 'droid') {
-    return normalized;
-  }
-
-  return null;
-}
-
 // ==================== Profile CRUD ====================
 
 /**
diff --git a/src/web-server/routes/proxy-routes.ts b/src/web-server/routes/proxy-routes.ts
index a8c92f84..2d9ba46d 100644
--- a/src/web-server/routes/proxy-routes.ts
+++ b/src/web-server/routes/proxy-routes.ts
@@ -8,7 +8,7 @@
  */
 
 import { Router, Request, Response } from 'express';
-import { loadOrCreateUnifiedConfig, saveUnifiedConfig } from '../../config/unified-config-loader';
+import { loadOrCreateUnifiedConfig, mutateUnifiedConfig } from '../../config/unified-config-loader';
 import { testConnection } from '../../cliproxy/remote-proxy-client';
 import { isProxyRunning } from '../../cliproxy/services/proxy-lifecycle-service';
 import { DEFAULT_BACKEND } from '../../cliproxy/platform-detector';
@@ -36,32 +36,32 @@ router.get('/', async (_req: Request, res: Response) => {
 /**
  * PUT /api/cliproxy-server - Update proxy configuration
  */
-router.put('/', async (req: Request, res: Response) => {
+router.put('/', (req: Request, res: Response) => {
   try {
-    const config = await loadOrCreateUnifiedConfig();
     const updates = req.body as Partial<CliproxyServerConfig>;
 
-    // Deep merge with defaults and current config
-    config.cliproxy_server = {
-      remote: {
-        ...DEFAULT_CLIPROXY_SERVER_CONFIG.remote,
-        ...config.cliproxy_server?.remote,
-        ...updates.remote,
-      },
-      fallback: {
-        ...DEFAULT_CLIPROXY_SERVER_CONFIG.fallback,
-        ...config.cliproxy_server?.fallback,
-        ...updates.fallback,
-      },
-      local: {
-        ...DEFAULT_CLIPROXY_SERVER_CONFIG.local,
-        ...config.cliproxy_server?.local,
-        ...updates.local,
-      },
-    };
+    // Atomic read-modify-write — avoids race between load and save
+    const updated = mutateUnifiedConfig((config) => {
+      config.cliproxy_server = {
+        remote: {
+          ...DEFAULT_CLIPROXY_SERVER_CONFIG.remote,
+          ...config.cliproxy_server?.remote,
+          ...updates.remote,
+        },
+        fallback: {
+          ...DEFAULT_CLIPROXY_SERVER_CONFIG.fallback,
+          ...config.cliproxy_server?.fallback,
+          ...updates.fallback,
+        },
+        local: {
+          ...DEFAULT_CLIPROXY_SERVER_CONFIG.local,
+          ...config.cliproxy_server?.local,
+          ...updates.local,
+        },
+      };
+    });
 
-    await saveUnifiedConfig(config);
-    res.json(config.cliproxy_server);
+    res.json(updated.cliproxy_server);
   } catch (error) {
     console.error('[cliproxy-server-routes] Failed to save proxy config:', error);
     res.status(500).json({ error: 'Failed to save proxy config' });
@@ -91,7 +91,7 @@ router.get('/backend', async (_req: Request, res: Response) => {
  * @throws {400} Invalid backend value
  * @throws {409} Proxy is running (unless force=true)
  */
-router.put('/backend', async (req: Request, res: Response) => {
+router.put('/backend', (req: Request, res: Response) => {
   try {
     const { backend, force } = req.body;
     if (backend !== 'original' && backend !== 'plus') {
@@ -99,9 +99,9 @@ router.put('/backend', async (req: Request, res: Response) => {
       return;
     }
 
-    // Check if proxy is running - warn about restart requirement
-    const config = await loadOrCreateUnifiedConfig();
-    const currentBackend = config.cliproxy?.backend ?? DEFAULT_BACKEND;
+    // Pre-flight read: check running state before acquiring write lock
+    const currentConfig = loadOrCreateUnifiedConfig();
+    const currentBackend = currentConfig.cliproxy?.backend ?? DEFAULT_BACKEND;
     if (currentBackend !== backend && isProxyRunning() && !force) {
       res.status(409).json({
         error: 'Proxy is running. Stop proxy first or use force=true to change backend.',
@@ -110,18 +110,21 @@ router.put('/backend', async (req: Request, res: Response) => {
       });
       return;
     }
-    if (!config.cliproxy) {
-      config.cliproxy = {
-        backend,
-        oauth_accounts: {},
-        providers: [...CLIPROXY_PROVIDER_IDS],
-        variants: {},
-      };
-    } else {
-      config.cliproxy.backend = backend;
-    }
 
-    await saveUnifiedConfig(config);
+    // Atomic write — avoids race between load and save
+    mutateUnifiedConfig((config) => {
+      if (!config.cliproxy) {
+        config.cliproxy = {
+          backend,
+          oauth_accounts: {},
+          providers: [...CLIPROXY_PROVIDER_IDS],
+          variants: {},
+        };
+      } else {
+        config.cliproxy.backend = backend;
+      }
+    });
+
     res.json({ backend });
   } catch (error) {
     console.error('[cliproxy-server-routes] Failed to save backend config:', error);
diff --git a/src/web-server/routes/route-helpers.ts b/src/web-server/routes/route-helpers.ts
index 4f5c048e..2b38e486 100644
--- a/src/web-server/routes/route-helpers.ts
+++ b/src/web-server/routes/route-helpers.ts
@@ -4,6 +4,7 @@
 
 import * as fs from 'fs';
 import * as path from 'path';
+import type { Response } from 'express';
 import { getCcsDir, getConfigPath, loadConfigSafe, loadSettings } from '../../utils/config-manager';
 import { expandPath } from '../../utils/helpers';
 import { getClaudeSettingsPath } from '../../utils/claude-config-path';
@@ -16,6 +17,7 @@ import {
 } from '../../cliproxy/model-id-normalizer';
 import type { CLIProxyProvider } from '../../cliproxy/types';
 import type { Config, Settings } from '../../types/config';
+import type { TargetType } from '../../targets/target-adapter';
 import { ValidationError } from '../../errors/error-types';
 
 /** Model mapping for API profiles */
@@ -389,3 +391,58 @@ export function validateFilePath(filePath: string): {
 
   return { valid: false, readonly: false, error: 'Access to this path is not allowed' };
 }
+
+/**
+ * Parse and validate a target param (claude/droid). Returns null if invalid/absent.
+ * Shared by profile-routes and variant-routes.
+ */
+export function parseTarget(rawTarget: unknown): TargetType | null {
+  if (rawTarget === undefined || rawTarget === null || rawTarget === '') {
+    return null;
+  }
+
+  if (typeof rawTarget !== 'string') {
+    return null;
+  }
+
+  const normalized = rawTarget.trim().toLowerCase();
+  if (normalized === 'claude' || normalized === 'droid') {
+    return normalized;
+  }
+
+  return null;
+}
+
+/**
+ * Create route-specific error helpers with a log prefix.
+ * Eliminates duplicate logRouteError/respondInternalError in each route file.
+ */
+export function createRouteErrorHelpers(prefix: string): {
+  logRouteError: (context: string, error: unknown) => void;
+  respondInternalError: (
+    res: Response,
+    error: unknown,
+    fallbackMessage: string,
+    statusCode?: number
+  ) => void;
+} {
+  function logRouteError(context: string, error: unknown): void {
+    if (error instanceof Error) {
+      console.error(`[${prefix}] ${context}: ${error.message}`);
+      return;
+    }
+    console.error(`[${prefix}] ${context}: unknown error`);
+  }
+
+  function respondInternalError(
+    res: Response,
+    error: unknown,
+    fallbackMessage: string,
+    statusCode = 500
+  ): void {
+    logRouteError(fallbackMessage, error);
+    res.status(statusCode).json({ error: fallbackMessage });
+  }
+
+  return { logRouteError, respondInternalError };
+}
diff --git a/src/web-server/routes/settings-routes.ts b/src/web-server/routes/settings-routes.ts
index 4d6a7af7..69dc878e 100644
--- a/src/web-server/routes/settings-routes.ts
+++ b/src/web-server/routes/settings-routes.ts
@@ -32,6 +32,7 @@ import {
   extractProviderFromPathname,
   getDeniedModelIdReasonForProvider,
 } from '../../cliproxy/model-id-normalizer';
+import { createRouteErrorHelpers } from './route-helpers';
 
 const router = Router();
 const MODEL_ENV_KEYS = [
@@ -42,23 +43,7 @@ const MODEL_ENV_KEYS = [
 ] as const;
 const PRESET_MODEL_KEYS = ['default', 'opus', 'sonnet', 'haiku'] as const;
 
-function logRouteError(context: string, error: unknown): void {
-  if (error instanceof Error) {
-    console.error(`[settings-routes] ${context}: ${error.message}`);
-    return;
-  }
-  console.error(`[settings-routes] ${context}: unknown error`);
-}
-
-function respondInternalError(
-  res: Response,
-  error: unknown,
-  fallbackMessage: string,
-  statusCode = 500
-): void {
-  logRouteError(fallbackMessage, error);
-  res.status(statusCode).json({ error: fallbackMessage });
-}
+const { logRouteError, respondInternalError } = createRouteErrorHelpers('settings-routes');
 
 function isLoopbackAddress(value: string | undefined): boolean {
   if (!value) return false;
diff --git a/src/web-server/routes/variant-routes.ts b/src/web-server/routes/variant-routes.ts
index 65a4c07b..7e9013ef 100644
--- a/src/web-server/routes/variant-routes.ts
+++ b/src/web-server/routes/variant-routes.ts
@@ -7,7 +7,7 @@
 import { Router, Request, Response } from 'express';
 import { isReservedName, RESERVED_PROFILE_NAMES } from '../../config/reserved-names';
 import type { CLIProxyProvider } from '../../cliproxy/types';
-import type { TargetType } from '../../targets/target-adapter';
+import { parseTarget } from './route-helpers';
 import {
   createVariant,
   removeVariant,
@@ -24,23 +24,6 @@ import {
 
 const router = Router();
 
-export function parseTarget(rawTarget: unknown): TargetType | null {
-  if (rawTarget === undefined || rawTarget === null || rawTarget === '') {
-    return null;
-  }
-
-  if (typeof rawTarget !== 'string') {
-    return null;
-  }
-
-  const normalized = rawTarget.trim().toLowerCase();
-  if (normalized === 'claude' || normalized === 'droid') {
-    return normalized;
-  }
-
-  return null;
-}
-
 /**
  * GET /api/cliproxy - List cliproxy variants
  * Uses variant-service for consistent behavior with CLI