diff --git a/public/sw.js b/public/sw.js
index ade69d1..3c2b889 100644
--- a/public/sw.js
+++ b/public/sw.js
@@ -1,8 +1,8 @@
 // CompetenceTrack — Service Worker for PWA Offline Support
-const CACHE_NAME = 'competencetrack-v2';
-const STATIC_CACHE = 'competencetrack-static-v2';
-const DATA_CACHE = 'competencetrack-data-v2';
-const OFFLINE_CACHE = 'competencetrack-offline-v2';
+const CACHE_NAME = 'competencetrack-v3';
+const STATIC_CACHE = 'competencetrack-static-v3';
+const DATA_CACHE = 'competencetrack-data-v3';
+const OFFLINE_CACHE = 'competencetrack-offline-v3';
 
 // Static assets to cache on install
 const STATIC_ASSETS = [
@@ -80,13 +80,20 @@ self.addEventListener('fetch', (event) => {
     return;
   }
 
-  // Static assets (CSS, JS, images) — CacheFirst strategy
-  // But use NetworkFirst for JS/CSS from Next.js dev server (_next/) to avoid stale module factories
+  // Never cache /_next/ paths — Turbopack recompiles frequently and cached chunks
+  // cause "module factory is not available" errors. Always fetch from network.
+  if (url.pathname.startsWith('/_next/')) {
+    event.respondWith(
+      fetch(request).catch(() => new Response('Offline', { status: 503 }))
+    );
+    return;
+  }
+
+  // Static assets (CSS, JS, images) from other origins — CacheFirst strategy
   if (
     url.pathname.endsWith('.css') ||
     url.pathname.endsWith('.js')
   ) {
-    // Always use NetworkFirst for JS/CSS to avoid stale Turbopack chunks
     event.respondWith(networkFirstStrategy(request, STATIC_CACHE));
     return;
   }
diff --git a/src/app/api/auth/route.ts b/src/app/api/auth/route.ts
index 4fa7708..7bd6baa 100644
--- a/src/app/api/auth/route.ts
+++ b/src/app/api/auth/route.ts
@@ -7,6 +7,9 @@ import {
   createSession,
   getSession,
   clearSession,
+  isSecureRequest,
+  SESSION_COOKIE_NAME,
+  getSessionCookieOptions,
 } from '@/lib/auth';
 import { withRateLimit, checkRateLimit, getRateLimitKey, getRateLimitHeaders, createRateLimitResponse } from '@/lib/rate-limit';
 
@@ -60,9 +63,13 @@ export const POST = withRateLimit(async function POST(request: Request) {
         );
       }
 
-      await createSession(user.id);
+      const secure = isSecureRequest(request);
+      await createSession(user.id, secure);
 
-      return NextResponse.json({
+      // Also set cookie on the response object to guarantee the Set-Cookie
+      // header is included. In some Next.js App Router scenarios, cookies().set()
+      // alone may not propagate to the NextResponse body.
+      const response = NextResponse.json({
         id: user.id,
         email: user.email,
         firstName: user.firstName,
@@ -72,6 +79,8 @@ export const POST = withRateLimit(async function POST(request: Request) {
         locale: user.locale,
         isDemo: user.isDemo,
       });
+      response.cookies.set(SESSION_COOKIE_NAME, user.id, getSessionCookieOptions(secure));
+      return response;
     }
 
     // ── Register ──
@@ -108,9 +117,10 @@ export const POST = withRateLimit(async function POST(request: Request) {
         },
       });
 
-      await createSession(user.id);
+      const secure = isSecureRequest(request);
+      await createSession(user.id, secure);
 
-      return NextResponse.json(
+      const response = NextResponse.json(
         {
           id: user.id,
           email: user.email,
@@ -123,28 +133,56 @@ export const POST = withRateLimit(async function POST(request: Request) {
         },
         { status: 201 }
       );
+      response.cookies.set(SESSION_COOKIE_NAME, user.id, getSessionCookieOptions(secure));
+      return response;
     }
 
     // ── Logout ──
     if (action === 'logout') {
       await clearSession();
-      return NextResponse.json({ message: 'Logged out' });
+
+      const response = NextResponse.json({ message: 'Logged out' });
+      response.cookies.delete(SESSION_COOKIE_NAME);
+      return response;
     }
 
     return NextResponse.json({ error: 'Unknown action' }, { status: 400 });
   } catch (error) {
-    console.error('Auth error:', error);
+    console.error('Auth POST error:', error);
+
+    // Return more specific error info for debugging
+    const message =
+      error instanceof Error ? error.message : 'Unknown error';
+    const isZod = error instanceof z.ZodError;
+    const isPrisma =
+      error instanceof Error &&
+      (error.message.includes('Prisma') || error.constructor.name.includes('Prisma'));
+
+    if (isZod) {
+      return NextResponse.json(
+        { error: 'Validation error', details: (error as z.ZodError).issues },
+        { status: 400 }
+      );
+    }
+
+    if (isPrisma) {
+      return NextResponse.json(
+        { error: 'Database error', detail: message },
+        { status: 500 }
+      );
+    }
+
     return NextResponse.json(
-      { error: 'Internal server error' },
+      { error: 'Internal server error', detail: message },
       { status: 500 }
     );
   }
 }, 'auth');
 
 export async function GET(request: Request) {
-  // Apply rate limit for auth check endpoint
+  // Apply rate limit for auth check endpoint — 120 per minute
   const key = getRateLimitKey(request);
-  const result = checkRateLimit(key, 60, 60 * 1000); // 60 per minute for GET
+  const result = checkRateLimit(key, 120, 60 * 1000);
 
   if (!result.allowed) {
     const rateLimitResponse = createRateLimitResponse(result);
@@ -167,9 +205,11 @@ export async function GET(request: Request) {
     }
     return response;
   } catch (error) {
-    console.error('Auth me error:', error);
+    console.error('Auth GET error:', error);
+    const message =
+      error instanceof Error ? error.message : 'Unknown error';
     return NextResponse.json(
-      { error: 'Internal server error' },
+      { error: 'Internal server error', detail: message },
       { status: 500 }
     );
   }
diff --git a/src/app/page.tsx b/src/app/page.tsx
index 260cc57..a080b2e 100644
--- a/src/app/page.tsx
+++ b/src/app/page.tsx
@@ -1,6 +1,6 @@
 'use client';
 
-import React, { useEffect } from 'react';
+import React, { useEffect, useRef } from 'react';
 import { useAppStore } from '@/lib/store';
 import { fetchCurrentUser } from '@/lib/api';
 import AuthView from '@/components/auth-view';
@@ -10,8 +10,13 @@ export default function Home() {
   const currentUser = useAppStore((s) => s.currentUser);
   const isLoadingAuth = useAppStore((s) => s.isLoadingAuth);
   const setCurrentUser = useAppStore((s) => s.setCurrentUser);
+  const hasCheckedRef = useRef(false);
 
   useEffect(() => {
+    // Prevent duplicate auth checks: only run once per component lifecycle
+    if (hasCheckedRef.current) return;
+    hasCheckedRef.current = true;
+
     async function checkAuth() {
       try {
         const user = await fetchCurrentUser();
diff --git a/src/components/offline-indicator.tsx b/src/components/offline-indicator.tsx
index 877c681..72c31cf 100644
--- a/src/components/offline-indicator.tsx
+++ b/src/components/offline-indicator.tsx
@@ -179,6 +179,9 @@ export function useServiceWorker() {
   useEffect(() => {
     if (typeof window === 'undefined') return;
     if (!('serviceWorker' in navigator)) return;
+    // Skip service worker registration during development to avoid stale
+    // Turbopack chunk caching ("module factory is not available" errors)
+    if (process.env.NODE_ENV === 'development') return;
 
     async function registerSW() {
       try {
diff --git a/src/components/ui/chart.tsx b/src/components/ui/chart.tsx
index 97cc280..4687cb6 100644
--- a/src/components/ui/chart.tsx
+++ b/src/components/ui/chart.tsx
@@ -78,12 +78,9 @@ const ChartStyle = ({ id, config }: { id: string; config: ChartConfig }) => {
     return null
   }
 
-  return (
-    <style
-      dangerouslySetInnerHTML={{
-        __html: Object.entries(THEMES)
-          .map(
-            ([theme, prefix]) => `
+  const cssText = Object.entries(THEMES)
+    .map(
+      ([theme, prefix]) => `
 ${prefix} [data-chart=${id}] {
 ${colorConfig
   .map(([key, itemConfig]) => {
@@ -95,11 +92,12 @@ ${colorConfig
   .join("\n")}
 }
 `
-          )
-          .join("\n"),
-      }}
-    />
-  )
+    )
+    .join("\n")
+
+  // Use ref to set textContent instead of dangerouslySetInnerHTML to avoid
+  // React 19 "Encountered a script tag" warning for style elements
+  return <style ref={(el) => { if (el) el.textContent = cssText }} />
 }
 
 const ChartTooltip = RechartsPrimitive.Tooltip
diff --git a/src/lib/auth.ts b/src/lib/auth.ts
index 39935c7..24251d9 100644
--- a/src/lib/auth.ts
+++ b/src/lib/auth.ts
@@ -3,8 +3,33 @@ import { cookies } from 'next/headers';
 import { Prisma } from '@prisma/client';
 import { db } from '@/lib/db';
 
-const SESSION_COOKIE_NAME = 'ct_session';
-const SESSION_COOKIE_MAX_AGE = 60 * 60 * 24 * 7; // 7 days
+export const SESSION_COOKIE_NAME = 'ct_session';
+export const SESSION_COOKIE_MAX_AGE = 60 * 60 * 24 * 7; // 7 days
+
+/**
+ * Determine whether the Secure flag should be set on cookies.
+ * Returns true when:
+ *  - NODE_ENV is production, OR
+ *  - the request came through an HTTPS proxy (x-forwarded-proto: https)
+ */
+export function isSecureRequest(request: Request): boolean {
+  if (process.env.NODE_ENV === 'production') return true;
+  const forwarded = request.headers.get('x-forwarded-proto');
+  return forwarded === 'https';
+}
+
+/**
+ * Returns the cookie options object for the session cookie.
+ */
+export function getSessionCookieOptions(secure: boolean) {
+  return {
+    httpOnly: true,
+    secure,
+    sameSite: 'lax' as const,
+    maxAge: SESSION_COOKIE_MAX_AGE,
+    path: '/',
+  };
+}
 
 export async function hashPassword(password: string): Promise<string> {
   const salt = await bcrypt.genSalt(10);
@@ -18,15 +43,10 @@ export async function verifyPassword(
   return bcrypt.compare(password, hash);
 }
 
-export async function createSession(userId: string): Promise<void> {
+export async function createSession(userId: string, secure?: boolean): Promise<void> {
   const cookieStore = await cookies();
-  cookieStore.set(SESSION_COOKIE_NAME, userId, {
-    httpOnly: true,
-    secure: process.env.NODE_ENV === 'production',
-    sameSite: 'lax',
-    maxAge: SESSION_COOKIE_MAX_AGE,
-    path: '/',
-  });
+  const cookieSecure = secure ?? (process.env.NODE_ENV === 'production');
+  cookieStore.set(SESSION_COOKIE_NAME, userId, getSessionCookieOptions(cookieSecure));
 }
 
 const sessionUserSelect = Prisma.validator<Prisma.UserSelect>()({
diff --git a/src/lib/rate-limit.ts b/src/lib/rate-limit.ts
index 2d44eb2..fb9e174 100644
--- a/src/lib/rate-limit.ts
+++ b/src/lib/rate-limit.ts
@@ -23,8 +23,11 @@ setInterval(() => {
 // ─── Preset Limits ────────────────────────────────────────────────────
 
 export const RATE_LIMITS = {
-  // Auth endpoints: 20 requests per minute (allows retries & multiple tabs)
-  auth: { limit: 20, windowMs: 60 * 1000 },
+  // Auth POST endpoints: 30 requests per minute (allows retries & multiple tabs)
+  auth: { limit: 30, windowMs: 60 * 1000 },
+
+  // Auth GET endpoint: 120 requests per minute (high frequency, low cost)
+  authGet: { limit: 120, windowMs: 60 * 1000 },
 
   // Data read endpoints: 60 requests per minute (generous)
   dataRead: { limit: 60, windowMs: 60 * 1000 },
diff --git a/src/lib/utils.ts b/src/lib/utils.ts
index b9f8576..4a39fd6 100644
--- a/src/lib/utils.ts
+++ b/src/lib/utils.ts
@@ -13,15 +13,25 @@ export function cn(...inputs: ClassValue[]) {
 export function sanitizeHtml(html: string): string {
   if (!html) return '';
   return html
-    // Remove <script> tags and their content
-    .replace(/<script\b[^<]*(?:(?!<\/script>)<[^<]*)*<\/script>/gi, '')
+    // Remove <script> tags and their content (handles multi-line, attributes, and unclosed tags)
+    .replace(/<script\b[\s\S]*?<\/script\s*>/gi, '')
+    // Remove unclosed <script> tags (no closing tag)
+    .replace(/<script\b[^>]*>[\s\S]*$/gi, '')
+    // Remove self-closing <script /> tags
+    .replace(/<script\b[^>]*\/>/gi, '')
     // Remove on* event handler attributes (onclick, onload, onerror, etc.)
     .replace(/\s+on\w+\s*=\s*(?:"[^"]*"|'[^']*'|[^\s>]+)/gi, '')
     // Remove javascript: URLs
     .replace(/href\s*=\s*(?:"javascript:[^"]*"|'javascript:[^']*')/gi, 'href="#"')
     // Remove <iframe> tags
-    .replace(/<iframe\b[^<]*(?:(?!<\/iframe>)<[^<]*)*<\/iframe>/gi, '')
+    .replace(/<iframe\b[\s\S]*?<\/iframe\s*>/gi, '')
     // Remove <object> and <embed> tags
-    .replace(/<object\b[^<]*(?:(?!<\/object>)<[^<]*)*<\/object>/gi, '')
-    .replace(/<embed\b[^>]*>/gi, '');
+    .replace(/<object\b[\s\S]*?<\/object\s*>/gi, '')
+    .replace(/<embed\b[^>]*>/gi, '')
+    // Remove <noscript> tags (may contain script-like content)
+    .replace(/<noscript\b[\s\S]*?<\/noscript\s*>/gi, '')
+    // Remove <link> tags (could load external scripts)
+    .replace(/<link\b[^>]*>/gi, '')
+    // Remove <meta> tags with http-equiv="refresh" (could redirect)
+    .replace(/<meta\b[^>]*http-equiv\s*=\s*["']?refresh["']?[^>]*>/gi, '');
 }
diff --git a/worklog.md b/worklog.md
index b4263d1..551e033 100644
--- a/worklog.md
+++ b/worklog.md
@@ -1,5 +1,34 @@
 # CompetenceTrack — Project Worklog
 
+---
+Task ID: 1
+Agent: fix-auth-500-and-session-issues
+Task: Fix Auth 500 Errors and Session Persistence Issues
+Date: 2025-01-28
+
+Work Log:
+- **Session persistence fix** (`src/lib/auth.ts` + `src/app/api/auth/route.ts`):
+  - Root cause: `cookies().set()` from `next/headers` may not reliably propagate the `Set-Cookie` header to the `NextResponse` body in Next.js App Router route handlers.
+  - Fix: Added `response.cookies.set()` on the `NextResponse` object for login, register, and logout actions, guaranteeing the cookie is sent.
+  - Added `isSecureRequest(request)` helper that checks `x-forwarded-proto: https` header (for HTTPS proxies like sslip.io) in addition to `NODE_ENV === 'production'` to determine the `Secure` cookie flag.
+  - Exported `SESSION_COOKIE_NAME`, `SESSION_COOKIE_MAX_AGE`, and `getSessionCookieOptions()` from `auth.ts` so the route handler can set cookies on the response with consistent options.
+  - `createSession()` now accepts an optional `secure` parameter.
+
+- **Excessive GET /api/auth 401 polling fix** (`src/app/page.tsx`):
+  - Added a `useRef(false)` guard (`hasCheckedRef`) to the auth-check `useEffect` so it only fires once per component lifecycle, preventing duplicate or repeated calls.
+
+- **Rate limit increase** (`src/lib/rate-limit.ts` + `src/app/api/auth/route.ts`):
+  - Auth POST rate limit: 20 → 30 req/min.
+  - Auth GET rate limit: 60 → 120 req/min (in both the `RATE_LIMITS.authGet` preset and the inline `checkRateLimit` call in the GET handler).
+  - Added `authGet` preset to `RATE_LIMITS` for future use.
+
+- **Better error handling** (`src/app/api/auth/route.ts`):
+  - POST catch block now distinguishes Zod validation errors, Prisma/database errors, and generic errors, returning specific messages and status codes.
+  - GET catch block now includes the error message in the response body for debugging.
+  - Error logs use `Auth POST error:` and `Auth GET error:` prefixes for easier log filtering.
+
+- Verification: `bun run lint` — 0 errors ✓
+
 ---
 Task ID: 26
 Agent: bug-fix-auth-500-script-tag-dynamic-import-rate-limit
@@ -1208,3 +1237,33 @@ Work Log:
   - bun run lint: 0 errors
   - Dev server running without errors
 
+---
+Task ID: 2
+Agent: fix-script-tag-warning-module-factory-error
+Task: Fix Script Tag Warning and Module Factory Error
+Date: 2025-01-27
+
+Work Log:
+- Fixed script tag warning in chart.tsx:
+  - Replaced `<style dangerouslySetInnerHTML={{...}}>` with `<style ref={(el) => { if (el) el.textContent = cssText }} />` in the ChartStyle component
+  - This avoids React 19's "Encountered a script tag" warning that is triggered for style elements using dangerouslySetInnerHTML
+  - The ref-based approach sets textContent synchronously during the commit phase, so no FOUC occurs
+- Improved sanitizeHtml function in utils.ts:
+  - Replaced the fragile `[^<]*` regex pattern with `[\s\S]*?` (non-greedy, matches any character including newlines)
+  - Added handling for unclosed `<script>` tags (no closing tag)
+  - Added handling for self-closing `<script />` tags
+  - Added removal of `<noscript>` tags (may contain script-like content)
+  - Added removal of `<link>` tags (could load external scripts)
+  - Added removal of `<meta>` tags with http-equiv="refresh" (could redirect)
+  - Updated iframe, object regex patterns to use `[\s\S]*?` for multi-line support
+- Fixed module factory error in service worker:
+  - Bumped cache version from v2 to v3 to force cache invalidation
+  - Added a dedicated `/_next/` path check that uses NetworkOnly strategy (never caches)
+  - This prevents stale Turbopack chunks from being served, which cause "module factory is not available" errors
+  - Comment explains why /_next/ paths must never be cached
+- Updated offline-indicator.tsx useServiceWorker hook:
+  - Added `process.env.NODE_ENV === 'development'` check to skip service worker registration during development
+  - This prevents the service worker from interfering with Turbopack's hot module replacement
+  - Service worker is only active in production builds
+- Verification: bun run lint passes with 0 errors
+