fix: simplify chat rendering, persist drawer size, fix auth guard (v2) (#335)

* fix: simplify chat rendering, persist drawer size, fix auth guard

- Simplify chat-messages.tsx: remove dual-path tailContent rendering,
  always use AssistantMessage for both stream and committed states
- Remove dead code: chat-status-state.ts (ThinkingGroup/ToolGroup/StatusTimer)
- Remove dead exports: busyStartedAt, composerPlaceholder from use-chat-session
- Fix ThinkingBlock label: remove hardcoded label="Thinking" so defaults
  work ("Thinking" shimmer → "Thought" static)
- Persist resizable drawer panel size in localStorage alongside open state
  to eliminate layout shift on page refresh
- Add busy grace period in use-chat-session for smooth stream→committed transition
- Accumulate reasoning parts across multi-step tool use in durable-chat-run
- Fix auth-guard: remove localSandboxMode bypass so login always works
- Fix chatThreads.getMessages: return [] instead of throwing when unauthenticated

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: remove unnecessary busy grace period

Convex reactive queries handle data consistency — no need for a 600ms
grace period to bridge the stream→committed transition.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: remove dead shouldShowToolsForAssistantSnapshot

Greptile P1: function was exported and tested but never called.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: stabilize resizable drawer defaultSize to prevent drag breakage

The aside panel's defaultSize prop included state.activeSize, which
changed on every drag frame. In react-resizable-panels, changing
defaultSize triggers panel de-registration and re-registration, which
destroys the active drag's panel references and prevents resizing.

Use useState initializer to capture the size once on mount and keep it
stable. The existing useEffect handles all open/close/resize via
panelRef imperatively.

Also clean up context-chip: split active/inactive into distinct
render paths, remove unused Plus import.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* fix: resolve ../ relative paths in file citations

Strip one leading ../ segment and resolve against rootPath's parent
instead of naively concatenating, which produced un-normalized routes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/coding-agent/test/durable-chat-run.test.ts

@@ -125,6 +125,75 @@ describe("DurableChatRunReporter", () => {
     });
   });
 
+  it("accumulates reasoning across multi-step tool use", async () => {
+    const fetchMock = vi.fn<typeof fetch>().mockResolvedValue(mockOkResponse());
+    vi.stubGlobal("fetch", fetchMock);
+
+    const reporter = new DurableChatRunReporter({
+      runId: "run-3",
+      callbackUrl: "https://web.example/api/chat/runs/run-3/events",
+      callbackToken: "callback-token",
+    });
+
+    const step1Message = {
+      role: "assistant",
+      timestamp: 100,
+      content: [
+        { type: "thinking", thinking: "step 1 reasoning" },
+        { type: "text", text: "step 1 text" },
+      ],
+    };
+
+    reporter.handleSessionEvent(
+      { type: "message_start", message: step1Message } as never,
+      [],
+    );
+    reporter.handleSessionEvent(
+      { type: "message_end", message: step1Message } as never,
+      [],
+    );
+
+    const step2Message = {
+      role: "assistant",
+      timestamp: 200,
+      content: [
+        { type: "thinking", thinking: "step 2 reasoning" },
+        { type: "text", text: "step 2 text" },
+      ],
+    };
+
+    reporter.handleSessionEvent(
+      { type: "message_start", message: step2Message } as never,
+      [],
+    );
+    reporter.handleSessionEvent(
+      { type: "message_end", message: step2Message } as never,
+      [],
+    );
+
+    await reporter.finalize({
+      ok: true,
+      response: "step 2 text",
+      sessionKey: "session-1",
+    });
+
+    const itemsCall = fetchMock.mock.calls.find((call) =>
+      String(call[1]?.body).includes('"items"'),
+    );
+    const body = JSON.parse(String(itemsCall?.[1]?.body)) as {
+      items: Array<{ partsJson: string }>;
+    };
+    const parts = JSON.parse(body.items[0]?.partsJson ?? "[]") as Array<{
+      type: string;
+      text?: string;
+    }>;
+
+    const reasoningParts = parts.filter((p) => p.type === "reasoning");
+    expect(reasoningParts).toHaveLength(2);
+    expect(reasoningParts[0]?.text).toBe("step 1 reasoning");
+    expect(reasoningParts[1]?.text).toBe("step 2 reasoning");
+  });
+
   it("marks aborted runs as interrupted", async () => {
     const fetchMock = vi.fn<typeof fetch>().mockResolvedValue(mockOkResponse());
     vi.stubGlobal("fetch", fetchMock);