Initial commit: opencode_bridge JupyterLab extension (Slices 1-3.5)

A JupyterLab extension that bridges the cell UI to a local OpenCode Serve
process. The extension is a dual package: a Python server extension
exposed under /opencode-bridge/*, plus a TypeScript frontend that
registers per-cell toolbars.

Backend (Python, tornado)
- Slice 1: config + auth + OpenCode HTTP client (tornado.httpclient,
  no aiohttp). 4 settings in schema/plugin.json (url, user, password,
  request timeout).
- Slice 2: handlers for /hello, /health, /providers, /edit.
- Slice 2.1 (correction): SessionManager with 1 notebook = 1 session
  mapping, async-safe via per-path locks, 404 recovery via invalidate().
  Two new endpoints: GET /sessions, DELETE /session?notebook=<path>.
- 32 pytest tests pass.

Frontend (TypeScript, JupyterLab 4.6)
- src/types.ts: CellContext, OpenCodeRequest/Response, OpenCodeSettings.
- src/context/cell_context.ts: extract CellContext from a CodeCell +
  its parent NotebookPanel, structured error collection.
- src/api/opencode_client.ts: callOpenCodeEdit, callOpenCodeProviders.
- src/components/opencode_cell_footer.ts: OpenCodeCellFooter Widget
  implementing ICellFooter with 3 buttons (optimize / fix / edit),
  resolved via this.parent instanceof CodeCell. NOT cellToolbar
  (does not exist in JL 4.6) and NOT Widget.findParent (removed in
  @lumino/widgets 2.x).
- src/components/opencode_cell_factory.ts: Cell.ContentFactory
  subclass returning the OpenCodeCellFooter.
- src/components/opencode_installer.ts: installOpenCodeEverywhere
  patches every notebook (existing + new) to use the custom factory.
- src/index.ts: registers the factory, loads settings, fetches
  /providers on activation and logs the list to the console.
- 23 jest tests pass (mocked JupyterLab boundary, pnpm path safe).

Settings
- 6 fields: 3 auth (url/user/password) + 1 timeout + 2 model selection
  (provider/model). Provider list is fetched at startup from
  /opencode-bridge/providers and printed to the browser console so
  users can copy values into Settings Editor.

Docs
- design.md: 6 sections covering architecture, UI flow, API contract,
  TS skeletons, session management (v0.2.1 correction), and
  provider/model selection (v0.2.2 addition).
- CLAUDE.md: agent guidance for working in this repo.
- TODO.md: remaining work for Slices 4-7 + v0.4+ backlog.

CI
- Gitea release workflow at .github/workflows/build.yml.
- Bark notification helper (non-fatal on failure).

Generated artefacts ignored: opencode_bridge/labextension/, _version.py,
*.tsbuildinfo, junit.xml, test.ipynb scratch notebook.

src/api/opencode_client.ts

@@ -0,0 +1,86 @@
+/**
+ * HTTP client for the opencode-bridge server extension.
+ */
+import { URLExt } from '@jupyterlab/coreutils';
+import { ServerConnection } from '@jupyterlab/services';
+
+import type { OpenCodeProvidersResponse, OpenCodeRequest, OpenCodeResponse } from '../types';
+
+/**
+ * Call POST /opencode-bridge/edit. Returns parsed response (success or failure).
+ * Throws on network error or non-JSON response.
+ */
+export async function callOpenCodeEdit(
+  request: OpenCodeRequest,
+  serverSettings: ServerConnection.ISettings
+): Promise<OpenCodeResponse> {
+  const url = URLExt.join(
+    serverSettings.baseUrl,
+    'opencode-bridge',
+    'edit'
+  );
+
+  const init: RequestInit = {
+    method: 'POST',
+    body: JSON.stringify(request),
+    headers: { 'Content-Type': 'application/json' },
+  };
+
+  let response: Response;
+  try {
+    response = await ServerConnection.makeRequest(url, init, serverSettings);
+  } catch (error) {
+    throw new Error(
+      `network error calling opencode-bridge: ${(error as Error).message}`
+    );
+  }
+
+  const text = await response.text();
+  if (!text) {
+    throw new Error(
+      `empty response from opencode-bridge (status ${response.status})`
+    );
+  }
+
+  let parsed: unknown;
+  try {
+    parsed = JSON.parse(text);
+  } catch (e) {
+    throw new Error(
+      `non-JSON response from opencode-bridge (status ${response.status})`
+    );
+  }
+
+  return parsed as OpenCodeResponse;
+}
+
+/**
+ * Call GET /opencode-bridge/providers. Returns the parsed JSON response.
+ * Throws on network error or non-2xx status.
+ */
+export async function callOpenCodeProviders(
+  serverSettings: ServerConnection.ISettings
+): Promise<OpenCodeProvidersResponse> {
+  const url = URLExt.join(
+    serverSettings.baseUrl,
+    'opencode-bridge',
+    'providers'
+  );
+
+  let response: Response;
+  try {
+    response = await ServerConnection.makeRequest(url, { method: 'GET' }, serverSettings);
+  } catch (error) {
+    throw new Error(
+      `network error calling opencode-bridge/providers: ${(error as Error).message}`
+    );
+  }
+
+  if (!response.ok) {
+    throw new Error(
+      `opencode-bridge/providers failed: ${response.status} ${response.statusText}`
+    );
+  }
+
+  return (await response.json()) as OpenCodeProvidersResponse;
+}