fix(auth): re-issue session cookie on each request (sliding expiry)

The codeman_session cookie was only set on the Basic Auth path with a fixed
lifetime from login and never refreshed, while the server-side session store
slides its TTL (refreshOnGet). So the browser cookie expired mid-use, the next
request arrived cookie-less and fell through to Basic Auth, popping the native
username/password dialog — perceived as a random logout while actively working.

Re-issue the cookie on every authenticated (valid-cookie) request so the browser
lifetime tracks the server-side sliding TTL.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/web/middleware/auth.ts

@@ -151,6 +151,19 @@ export function registerAuthMiddleware(app: FastifyInstance, https: boolean): Au
     // Use get() instead of has() so refreshOnGet extends the TTL on active sessions
     const sessionToken = req.cookies[AUTH_COOKIE_NAME];
     if (sessionToken && authSessions.get(sessionToken) !== undefined) {
+      // Sliding cookie: re-issue on every authenticated request so the browser
+      // cookie lifetime tracks the server-side sliding TTL (refreshOnGet above).
+      // Without this the cookie has a fixed lifetime from login; the browser
+      // drops it mid-use, the next request arrives cookie-less and falls through
+      // to Basic Auth — popping the native username/password dialog, which reads
+      // as a random logout while actively working.
+      reply.setCookie(AUTH_COOKIE_NAME, sessionToken, {
+        httpOnly: true,
+        secure: https,
+        sameSite: 'lax',
+        maxAge: AUTH_SESSION_TTL_MS / 1000, // seconds
+        path: '/',
+      });
       done();
       return;
     }