fix(browse): extension token bootstrap moves to pinned-origin POST; /health carries no token

GET /health is now liveness/status only in every mode — both token
carve-outs (headed-mode disjunct AND chrome-extension:// Origin
disjunct) are removed. Token bootstrap is POST /extension-token on the
local listener: the Origin header must be exactly
chrome-extension://<GSTACK_EXTENSION_ID> and the Host header's hostname
must parse to 127.0.0.1 or localhost (parsed via new URL, never literal
equality — Host arrives as '127.0.0.1:34567'). Wrong origin/host → 403
with no detail. The tunnel surface 404s the endpoint (not in
TUNNEL_PATHS, verified by test).

The extension ID is pinned by a new "key" field (RSA public key) in
extension/manifest.json; browse/scripts/extension-id.ts reproduces the
ID derivation (first 16 bytes of SHA-256 of the DER public key, hex
mapped 0-9a-f → a-p). The private key is not committed anywhere —
unpacked/baked-in loads only need the public key.

Extension side: background.js bootstraps and refreshes the token via
POST /extension-token (403 → disconnected state); sidepanel.js direct
connect path does the same; sidepanel-terminal.js's dead /health token
fallback (read AUTH_TOKEN/authToken keys the server never sent,
hardcoded port) is replaced with the window.gstackAuthToken path.

MIGRATION NOTE: the manifest key pins the extension ID, so existing
installs' side-panel local state (saved port, snoozes) resets once —
explained in-product via a one-time notice (flag
gstack_id_migrated_v162). After upgrading the server, restart the
browser so the old service worker stops polling for a token GET /health
no longer serves.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
(cherry picked from commit e9a0b6847a2d17fe6656a4686b4efd0c8380eb09)

browse/test/pair-agent-e2e.test.ts

@@ -22,6 +22,7 @@ import { describe, test, expect, beforeAll, afterAll } from 'bun:test';
 import * as fs from 'fs';
 import * as os from 'os';
 import * as path from 'path';
+import { GSTACK_EXTENSION_ID } from '../src/server';
 
 const ROOT = path.resolve(import.meta.dir, '../..');
 const SERVER_ENTRY = path.join(ROOT, 'browse/src/server.ts');
@@ -94,22 +95,44 @@ describe('pair-agent flow end-to-end (HTTP only, no ngrok)', () => {
     if (daemon) killDaemon(daemon);
   });
 
-  test('GET /health returns daemon status and includes token for chrome-extension origin', async () => {
+  test('GET /health returns daemon status and NEVER includes a token (even for chrome-extension origins)', async () => {
     const resp = await fetch(`${daemon.baseUrl}/health`, {
-      headers: { Origin: 'chrome-extension://test-extension-id' },
+      headers: { Origin: `chrome-extension://${GSTACK_EXTENSION_ID}` },
     });
     expect(resp.status).toBe(200);
     const body = await resp.json() as any;
     expect(body.status).toBeDefined();
-    // Extension bootstrap — local listener delivers the token
-    expect(body.token).toBe(daemon.token);
+    // v1.62: token bootstrap moved to POST /extension-token. /health is
+    // liveness-only in every mode.
+    expect(body.token).toBeUndefined();
   });
 
-  test('GET /health without chrome-extension origin does NOT include token', async () => {
+  test('GET /health without origin does NOT include token', async () => {
     const resp = await fetch(`${daemon.baseUrl}/health`);
     expect(resp.status).toBe(200);
     const body = await resp.json() as any;
-    // Headless mode + no chrome-extension origin → token withheld
+    expect(body.token).toBeUndefined();
+  });
+
+  test('POST /extension-token with pinned Origin over real HTTP (Host carries port) returns the token', async () => {
+    // Real fetch → Host arrives as '127.0.0.1:<port>'; the server must parse
+    // the hostname out rather than compare the raw header (amendment C9).
+    const resp = await fetch(`${daemon.baseUrl}/extension-token`, {
+      method: 'POST',
+      headers: { Origin: `chrome-extension://${GSTACK_EXTENSION_ID}` },
+    });
+    expect(resp.status).toBe(200);
+    const body = await resp.json() as any;
+    expect(body.token).toBe(daemon.token);
+  });
+
+  test('POST /extension-token with a non-pinned extension Origin returns 403 without the token', async () => {
+    const resp = await fetch(`${daemon.baseUrl}/extension-token`, {
+      method: 'POST',
+      headers: { Origin: 'chrome-extension://aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa' },
+    });
+    expect(resp.status).toBe(403);
+    const body = await resp.json() as any;
     expect(body.token).toBeUndefined();
   });