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>

opencode_bridge/routes.py

@@ -249,6 +249,58 @@ class SessionReleaseHandler(APIHandler):
         }))
 
 
+class SessionMessagesHandler(APIHandler):
+    """List the current session's messages for a notebook (scrollable history).
+
+    Query param: notebook=<notebook path, URL-encoded>
+    Returns: { messages: [{ role: "user"|"assistant", content: string }] }
+    If no session exists for the notebook yet, returns { messages: [] }
+    (does NOT create a session just to report emptiness).
+    """
+
+    @tornado.web.authenticated
+    async def get(self):
+        notebook_path = self.get_query_argument("notebook", "")
+        if not notebook_path:
+            self.set_status(400)
+            self.finish(json.dumps({"error": "missing 'notebook' query parameter"}))
+            return
+        sm = get_session_manager(self)
+        sid = sm.peek(notebook_path)
+        if sid is None:
+            self.finish(json.dumps({"messages": []}))
+            return
+        try:
+            client = make_client(self)
+            raw = await client.list_session_messages(sid)
+        except OpenCodeError as e:
+            if "404" in str(e) or "not found" in str(e).lower():
+                sm.invalidate(notebook_path)
+                log.warning("invalidated dead session for %s", notebook_path)
+            log.exception("list session messages failed")
+            self.set_status(502)
+            self.finish(json.dumps({"ok": False, "error": str(e)}))
+            return
+        except Exception as e:
+            log.exception("list session messages failed")
+            self.set_status(502)
+            self.finish(json.dumps({"ok": False, "error": str(e)}))
+            return
+
+        # Project OpenCode's {info, parts}[] into a frontend-friendly
+        # {role, content}[] by joining the text parts.
+        messages = []
+        for m in raw or []:
+            info = m.get("info") or {}
+            role = info.get("role") or "assistant"
+            parts = m.get("parts") or []
+            content = "\n".join(
+                p.get("text", "") for p in parts if p.get("type") == "text"
+            ).strip()
+            messages.append({"role": role, "content": content})
+        self.finish(json.dumps({"messages": messages}))
+
+
 def setup_route_handlers(web_app):
     host_pattern = ".*$"
     base_url = web_app.settings["base_url"]
@@ -260,6 +312,7 @@ def setup_route_handlers(web_app):
         (url_path_join(base_url, "opencode-bridge", "edit"), EditHandler),
         (url_path_join(base_url, "opencode-bridge", "sessions"), SessionListHandler),
         (url_path_join(base_url, "opencode-bridge", "session"), SessionReleaseHandler),
+        (url_path_join(base_url, "opencode-bridge", "session-messages"), SessionMessagesHandler),
     ]
 
     web_app.add_handlers(host_pattern, handlers)