feat(chat): unify session gateway with stable IDs and a single WS protocol

The frontend previously juggled placeholder IDs, provider-native IDs, and session_created handoffs, which caused race conditions and provider-specific branching. This introduces app-allocated session IDs, a chat run registry with event replay, delta sidebar updates, and one kind-based websocket contract so the UI can treat every provider the same while JSONL remains the source of truth.

src/components/app/AppContent.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useRef } from 'react';
+import { useEffect } from 'react';
 import { useNavigate, useParams } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
 
@@ -24,8 +24,7 @@ function AppContentInner() {
   const { sessionId } = useParams<{ sessionId?: string }>();
   const { t } = useTranslation('common');
   const { isMobile } = useDeviceSettings({ trackPWA: false });
-  const { ws, sendMessage, latestMessage, isConnected } = useWebSocket();
-  const wasConnectedRef = useRef(false);
+  const { ws, sendMessage, subscribe } = useWebSocket();
 
   const {
     processingSessions,
@@ -52,7 +51,7 @@ function AppContentInner() {
   } = useProjectsState({
     sessionId,
     navigate,
-    latestMessage,
+    subscribe,
     isMobile,
     activeSessions: processingSessions,
   });
@@ -96,23 +95,9 @@ function AppContentInner() {
     };
   }, [navigate, refreshProjectsSilently, setActiveTab, setSidebarOpen]);
 
-  // Permission recovery: query pending permissions on WebSocket reconnect or session change
-  useEffect(() => {
-    const isReconnect = isConnected && !wasConnectedRef.current;
-
-    if (isReconnect) {
-      wasConnectedRef.current = true;
-    } else if (!isConnected) {
-      wasConnectedRef.current = false;
-    }
-
-    if (isConnected && selectedSession?.id) {
-      sendMessage({
-        type: 'get-pending-permissions',
-        sessionId: selectedSession.id
-      });
-    }
-  }, [isConnected, selectedSession?.id, sendMessage]);
+  // Pending tool permissions are recovered through the `chat.subscribe` flow:
+  // the `chat_subscribed` ack carries them on session open and on reconnect,
+  // so no separate permission-recovery message is needed here.
 
   // Adjust the app container to stay above the virtual keyboard on iOS Safari.
   // On Chrome for Android the layout viewport already shrinks when the keyboard opens,
@@ -177,7 +162,6 @@ function AppContentInner() {
           setActiveTab={setActiveTab}
           ws={ws}
           sendMessage={sendMessage}
-          latestMessage={latestMessage}
           isMobile={isMobile}
           onMenuClick={() => setSidebarOpen(true)}
           isLoading={isLoadingProjects}