feat: inline prompt history area — scrollable session messages

The inline prompt now shows the current session's full message
history (user + assistant), scrollable, replacing the single-output
display from the previous commit. The user can scroll back through
prior exchanges in the same notebook's OpenCode session.

Server (opencode_bridge/):
  - New route: GET /opencode-bridge/session-messages?notebook=<path>
    - Resolves notebook to session via SessionManager.peek (no create).
    - If no session: {"messages": []} (no OpenCode call).
    - Else: GET /session/{id}/message on OpenCode Serve, project the
      raw {info, parts}[] into a frontend-friendly {role, content}[].
  - OpenCodeClient.list_session_messages(sid).
  - SessionManager.peek(notebook_path) -> Optional[str] (read without
    creating, to avoid spawning a session just to report emptiness).
  - Wired the new route in setup_route_handlers.

Client (src/):
  - types.ts: OpenCodeMessage { role, content } + OpenCodeMessagesResponse.
  - api/opencode_client.ts: callOpenCodeSessionMessages(notebook, serverSettings).
  - components/opencode_inline_prompt.ts:
    - Replaces the single .opencode-inline-output area with a
      scrollable .opencode-inline-history (max-height 320px, overflow-y
      auto, auto-scrolls to bottom on update).
    - setMessages(messages): renders user messages as plain text,
      assistant messages via marked.parse. No more setOutput/hideOutput.
  - components/opencode_cell_actions.ts:
    - _showPrompt now fires a _refreshHistory(notebookPath) which
      fetches and calls prompt.setMessages.
    - _handleResponse on success also calls _refreshHistory (the new
      assistant message appears as the last item in the history).
    - Cell source is still NOT replaced.
  - api/opencode_client module is mocked in the cell_actions test to
    avoid jsdom network calls.

style/base.css:
  - .opencode-inline-output* rules replaced with .opencode-inline-history
    (max-height 320px, overflow-y auto, border, padding) and
    .opencode-msg / .opencode-msg-user / .opencode-msg-assistant.
  - pre/code/p/h1-3 content styling scoped under .opencode-inline-history.

Tests:
  - pytest 37/37: FakeOpenCodeClient.list_session_messages + 3 new
    session_messages route tests (no session, projects messages, 400).
  - jest 29/29: setMessages renders user/assistant + history area tests.
  - FakeSessionManager.peek (returns None when session_id is falsy).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/components/opencode_cell_actions.ts

@@ -16,7 +16,7 @@ import type { NotebookPanel } from '@jupyterlab/notebook';
 import { ServerConnection } from '@jupyterlab/services';
 import { Widget } from '@lumino/widgets';
 
-import { callOpenCodeEdit } from '../api/opencode_client';
+import { callOpenCodeEdit, callOpenCodeSessionMessages } from '../api/opencode_client';
 import { extractCellContext } from '../context/cell_context';
 import type {
   CellContext,
@@ -123,6 +123,31 @@ export class OpenCodeCellActions extends Widget {
     });
     Widget.attach(prompt, this._cell.node);
     this._prompt = prompt;
+
+    // Fetch the current session's message history and render it into
+    // the prompt's scrollable history area. Empty list (no session yet)
+    // is a normal no-op render.
+    const notebookPath = this._context?.notebookPath;
+    if (notebookPath) {
+      void this._refreshHistory(notebookPath);
+    }
+  }
+
+  private async _refreshHistory(notebookPath: string): Promise<void> {
+    if (!_serverSettings || !this._prompt) {
+      return;
+    }
+    try {
+      const resp = await callOpenCodeSessionMessages(
+        notebookPath,
+        _serverSettings
+      );
+      this._prompt.setMessages(resp.messages);
+    } catch (e) {
+      // Non-fatal: the history is a convenience. The user can still
+      // send new prompts; just the scrollback won't update.
+      console.warn('opencode_bridge: failed to fetch session messages', e);
+    }
   }
 
   private _hidePrompt(): void {
@@ -172,11 +197,12 @@ export class OpenCodeCellActions extends Widget {
   private _handleResponse(resp: OpenCodeResponse): void {
     this._status = 'idle';
     if (resp.ok) {
-      // Display the AI response in the inline prompt's output area as
-      // rendered markdown. The cell source is NOT replaced — the user
-      // decides what to do with the output (close it, or resend).
-      if (this._prompt) {
-        this._prompt.setOutput(resp.markdown);
+      // Refetch the (now-updated) session history and render the new
+      // assistant message as the last item in the scrollable history.
+      // The cell source is NOT replaced.
+      const notebookPath = this._context?.notebookPath;
+      if (notebookPath) {
+        void this._refreshHistory(notebookPath);
       }
       Notification.info(
         `OpenCode 完成 (${resp.markdown.length} chars). Session: ${resp.sessionId.slice(0, 8)}…`