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/__tests__/vault.test.ts

@@ -116,7 +116,9 @@ function makeState(wasm: ReturnType<typeof makeWasm>): PopupState {
 const BASE_MSG = {
   config: { hostType: 'gitea' as const, hostUrl: 'https://g', repoPath: 'u/v', apiToken: 't' },
   passphrase: 'pw',
-  carrierImageBytes: new Uint8Array([0, 0, 0]).buffer,
+  // Must begin with the JPEG SOI magic (0xFF 0xD8) to pass handleCreateVault's
+  // pre-embed format guard; the WASM embed itself is mocked.
+  carrierImageBytes: new Uint8Array([0xff, 0xd8, 0x00]).buffer,
   deviceName: 'Dev',
 };
 
@@ -214,6 +216,30 @@ describe('handleCreateVault', () => {
     // Ownership was NOT transferred — setCurrent must NOT have been called.
     expect(setCurrent).not.toHaveBeenCalled();
   });
+
+  it('rejects a non-JPEG carrier with carrier_image_not_jpeg before touching WASM', async () => {
+    const wasm = makeWasm();
+    const state = makeState(wasm);
+    // PNG magic — must be classified, not handed to embed_image_secret.
+    const png = { ...BASE_MSG, carrierImageBytes: new Uint8Array([0x89, 0x50, 0x4e, 0x47]).buffer };
+
+    const resp = await vault.handleCreateVault(png, state);
+
+    expect(resp).toEqual({ ok: false, error: 'carrier_image_not_jpeg' });
+    expect(wasm.embed_image_secret).not.toHaveBeenCalled();
+    expect(wasm.unlock).not.toHaveBeenCalled();
+  });
+
+  it('rejects an empty carrier with carrier_image_empty', async () => {
+    const wasm = makeWasm();
+    const state = makeState(wasm);
+    const empty = { ...BASE_MSG, carrierImageBytes: new ArrayBuffer(0) };
+
+    const resp = await vault.handleCreateVault(empty, state);
+
+    expect(resp).toEqual({ ok: false, error: 'carrier_image_empty' });
+    expect(wasm.embed_image_secret).not.toHaveBeenCalled();
+  });
 });
 
 // --- attach_vault ---