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/server-auth.test.ts

@@ -22,14 +22,29 @@ function sliceBetween(source: string, startMarker: string, endMarker: string): s
 }
 
 describe('Server auth security', () => {
-  // Test 1: /health serves token conditionally (headed mode or chrome extension only)
-  test('/health serves token only in headed mode or to chrome extensions', () => {
+  // Test 1 (IRON RULE, inverted in v1.62): /health NEVER serves a token in
+  // ANY mode. Both carve-outs (headed-mode disjunct + chrome-extension://
+  // Origin disjunct) are gone. Token bootstrap moved to POST /extension-token
+  // with a pinned extension Origin.
+  test('/health never serves a token — no headed-mode or chrome-extension carve-out', () => {
     const healthBlock = sliceBetween(SERVER_SRC, "url.pathname === '/health'", "url.pathname === '/connect'");
-    // v1.35.0.0: AUTH_TOKEN const was deleted; factory uses cfg-derived authToken.
-    // Token must be conditional, not unconditional
-    expect(healthBlock).toContain('token: authToken');
-    expect(healthBlock).toContain('headed');
-    expect(healthBlock).toContain('chrome-extension://');
+    expect(healthBlock).not.toContain('token: authToken');
+    expect(healthBlock).not.toContain("getConnectionMode() === 'headed'");
+    expect(healthBlock).not.toContain("startsWith('chrome-extension://')");
+  });
+
+  // Test 1a: the pinned-origin bootstrap endpoint exists and gates on both
+  // the exact extension Origin and a loopback Host.
+  test('POST /extension-token gates on pinned Origin and loopback Host', () => {
+    const tokenBlock = sliceBetween(SERVER_SRC, "url.pathname === '/extension-token'", "url.pathname === '/health'");
+    expect(tokenBlock).toContain('GSTACK_EXTENSION_ID');
+    expect(tokenBlock).toContain('token: authToken');
+    // Host is parsed to a hostname (arrives as '127.0.0.1:34567'), never
+    // compared literally against the raw header.
+    expect(tokenBlock).toContain('.hostname');
+    expect(tokenBlock).toContain("'127.0.0.1'");
+    expect(tokenBlock).toContain("'localhost'");
+    expect(tokenBlock).toContain('403');
   });
 
   // Test 1b: /health does not expose sensitive browsing state