web(coder UI): ChatInput migration + Thinking render + DiffPanel route fix

Bundles in-progress working-tree UI work not authored this session (CoderPane ChatInput migration, AgentComposerBar/CoderMessageList/tab-bar/sidebar/pane refinements, provider icons) with this session's changes to the same files: MessageBubble renders a collapsible 'Thinking' block from reasoning_text/reasoning_parts (surfacing ACP agent_thought_chunk + native reasoning), and the DiffPanel approve/reject calls are repointed to the real /api/coder/pending/:id/apply and /reject routes (the old /sessions/:id/pending/:id/approve|reject paths did not exist).

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

apps/web/src/hooks/useSessionStream.ts

@@ -294,5 +294,21 @@ export function useSessionStream(sessionId: string | undefined) {
     };
   }, [sessionId]);
 
+  useEffect(() => {
+    if (!sessionId) return;
+    return sessionEvents.subscribe((event) => {
+      if (event.type === 'refetch_messages') {
+        void api.messages
+          .list(sessionId)
+          .then((messages) => {
+            setState((s) => applyFrame(s, { type: 'snapshot', messages }));
+          })
+          .catch((err: unknown) => {
+            console.warn('refetch_messages failed', err);
+          });
+      }
+    });
+  }, [sessionId]);
+
   return state;
 }