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/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(