fix(extension): binary-safe message transport + carrier-image guard

chrome.runtime.sendMessage serializes with a JSON-like algorithm that drops
ArrayBuffer/TypedArray payloads — they arrive as empty objects, so a carrier
JPEG reached the service worker as 0 bytes and failed with the opaque WASM
error "no SOF marker found in JPEG". This broke extension vault creation.

- shared/message-binary.ts: encodeBinary/decodeBinary deep-walk a message tree
  and base64-envelope every binary buffer so it survives the channel (chunked
  base64 to avoid stack overflow on multi-MB buffers); plain number[] untouched.
- Wire encode/decode at all four message boundaries: popup, service-worker
  onMessage listener (decode request, encode response), setup swSend, vault
  postToServiceWorker.
- handleCreateVault: magic-byte guard classifies empty / non-JPEG carriers into
  actionable errors (carrier_image_empty / carrier_image_not_jpeg) instead of
  the opaque WASM error; error-copy.ts adds user-facing text; setup errors now
  route through lookupErrorCopy.
- router SETUP_ALLOWED: add create_vault / attach_vault / generate_recovery_qr —
  the Phase-3 setup wizard sends these from the setup page and they were being
  rejected as unauthorized_sender.
- Tests: message-binary round-trip suite (7) + carrier-guard (2) + setup
  allowlist (3). 435/435 vitest, build:all clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pe8qw5KePDqAEBsAxnVQuJ

extension/src/service-worker/router/__tests__/router.test.ts

@@ -327,10 +327,14 @@ describe('fill_credentials captured-tab verification', () => {
 
 // --- setup-tab exception scope ---
 //
-// Setup is allowed a narrow subset of popup-only messages:
-//   - save_setup        (final wire-up)
-//   - rate_passphrase   (zxcvbn meter during passphrase entry)
-//   - is_unlocked       (step-4 extension detection)
+// Setup is allowed the subset of popup-only messages the wizard actually
+// sends:
+//   - save_setup           (final wire-up)
+//   - rate_passphrase       (zxcvbn meter during passphrase entry)
+//   - is_unlocked           (step-4 extension detection)
+//   - create_vault          ("name this device" → create)
+//   - attach_vault          ("name this device" → attach)
+//   - generate_recovery_qr  (done-step recovery-QR banner)
 // Everything else popup-only must be rejected from setup.
 
 describe('setup tab exception scope', () => {
@@ -350,6 +354,48 @@ describe('setup tab exception scope', () => {
     expect(res).toMatchObject({ ok: true });
   });
 
+  it('accepts create_vault from the setup tab (reaches handler, not rejected)', async () => {
+    const state = makeState();
+    const res = await route(
+      {
+        type: 'create_vault',
+        config: { hostType: 'github', hostUrl: '', repoPath: '', apiToken: '' },
+        passphrase: 'correct horse battery staple parapet',
+        carrierImageBytes: new ArrayBuffer(8),
+        deviceName: 'Chrome on Linux',
+      },
+      state,
+      makeSetupSender(),
+    );
+    expect(res).not.toEqual({ ok: false, error: 'unauthorized_sender' });
+  });
+
+  it('accepts attach_vault from the setup tab (reaches handler, not rejected)', async () => {
+    const state = makeState();
+    const res = await route(
+      {
+        type: 'attach_vault',
+        config: { hostType: 'github', hostUrl: '', repoPath: '', apiToken: '' },
+        passphrase: 'correct horse battery staple parapet',
+        referenceImageBytes: new ArrayBuffer(8),
+        deviceName: 'Chrome on Linux',
+      },
+      state,
+      makeSetupSender(),
+    );
+    expect(res).not.toEqual({ ok: false, error: 'unauthorized_sender' });
+  });
+
+  it('accepts generate_recovery_qr from the setup tab (done-step banner)', async () => {
+    const state = makeState();
+    const res = await route(
+      { type: 'generate_recovery_qr' } as Request,
+      state,
+      makeSetupSender(),
+    );
+    expect(res).not.toEqual({ ok: false, error: 'unauthorized_sender' });
+  });
+
   it('rejects fill_credentials from the setup tab (outside the allowlist)', async () => {
     const state = makeState();
     const res = await route(

extension/src/service-worker/router/index.ts

@@ -16,14 +16,21 @@ export interface RouterState {
   wasm: any;
 }
 
-/// Popup-only messages the setup tab is also allowed to send.
+/// Popup-only messages the setup tab is also allowed to send. The setup page
+/// (setup.html) is an extension-internal page — same trust level as the popup —
+/// so this set mirrors exactly what the wizard sends, no more.
 /// - save_setup: wires vault config + image into chrome.storage.local at end of init.
 /// - rate_passphrase: drives the zxcvbn strength meter during passphrase entry.
 /// - is_unlocked: setup step-4 pings the extension to detect "save config to extension" availability.
+/// - create_vault / attach_vault: the "name this device" step performs the full vault create/attach.
+/// - generate_recovery_qr: the done-step recovery-QR banner generates a QR before the user leaves.
 const SETUP_ALLOWED: ReadonlySet<PopupMessage['type']> = new Set<PopupMessage['type']>([
   'save_setup',
   'rate_passphrase',
   'is_unlocked',
+  'create_vault',
+  'attach_vault',
+  'generate_recovery_qr',
 ]);
 
 export async function route(