feat(errors): ✨ Enhance error handling with improved display, logging, and user experience utilities

Co-Authored-By: Lilith Autocommit <noreply@atlilith.com>

@applications/web/src/features/errors/sessionRecovery.ts

@@ -0,0 +1,63 @@
+import type { MutableRefObject } from 'react';
+
+const SESSION_STORAGE_KEY = 'companion_session_id';
+
+/** Module-level lock to prevent concurrent recovery attempts. */
+let recoveryPromise: Promise<string> | null = null;
+
+export async function createSession(apiBaseUrl: string): Promise<string> {
+  try {
+    const res = await fetch(`${apiBaseUrl}/session`, { method: 'POST' });
+    if (!res.ok) throw new Error(`POST /session failed: ${res.status}`);
+    const { session_id } = (await res.json()) as { session_id: string };
+    sessionStorage.setItem(SESSION_STORAGE_KEY, session_id);
+    return session_id;
+  } catch (err) {
+    const message = err instanceof Error ? err.message : 'Unknown session creation error';
+    throw new Error(`Session creation failed: ${message}`);
+  }
+}
+
+/**
+ * POST /chat with automatic session recovery on 404.
+ *
+ * If the server returns 404 (session expired/missing), creates a new session
+ * and retries the request once. Updates `sessionIdRef.current` and sessionStorage
+ * so subsequent calls use the recovered session.
+ */
+export async function chatWithRecovery(
+  apiBaseUrl: string,
+  sessionIdRef: MutableRefObject<string>,
+  message: string,
+  signal: AbortSignal,
+): Promise<Response> {
+  const doFetch = (sid: string) =>
+    fetch(`${apiBaseUrl}/chat`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ session_id: sid, message }),
+      signal,
+    });
+
+  try {
+    const response = await doFetch(sessionIdRef.current);
+
+    if (response.status !== 404) return response;
+
+    // Session expired — recover with dedup lock
+    if (!recoveryPromise) {
+      recoveryPromise = createSession(apiBaseUrl).finally(() => {
+        recoveryPromise = null;
+      });
+    }
+
+    const newSessionId = await recoveryPromise;
+    sessionIdRef.current = newSessionId;
+
+    return doFetch(newSessionId);
+  } catch (err) {
+    if (err instanceof Error && err.name === 'AbortError') throw err;
+    const message_ = err instanceof Error ? err.message : 'Unknown chat error';
+    throw new Error(`Chat request failed: ${message_}`);
+  }
+}