feat: invite-code mode for cross-device RP flows (WDP-73 / APP-9428)

[SeanROlszewski]

Summary

Adds a code-based discovery channel to the existing Bridge proof flow. Instead of clicking a deeplink or scanning a QR code, an RP shows the user a 6-character code; the user types it into World App on their phone and completes the existing Selfie Check / proof flow. Same proof flow, same poll loop, same Status enum — only the discovery channel changes.

• Wire shape matches wallet-bridge (APP-9425) and world-app-ios (APP-9424). Code is 6-char Crockford Base32 (5 random + 1 weighted check digit). HKDF-SHA256, no salt, IKM = canonical code's UTF-8 bytes; info="dx" → lookup index (lowercase hex), info="key" → AES-256-GCM key. The encryption key never reaches Bridge — only the index and ciphertext do. iv and payload are sent as standard base64, matching the URL/QR path.
• Cross-device-first by product reality (Reddit × World): the original WDP-73 mermaid's delivery_token mechanism is fundamentally same-device (universal links route to the device that opened them), so we drop it from idkit's surface entirely. Anti-collusion in the code path now degrades to "10-min TTL + one-shot redeem + per-IP rate limit" — see the spec for the full discussion.
• session_nonce Bearer auth sent on GET /response/:id for forward compatibility with wallet-bridge's session-nonce gate (release-blocking follow-up on Bridge). URL/QR connections keep session_nonce: None and the header is omitted, so existing bridge behavior is unchanged.
• Adopter diff is two lines per integration:

  // before
  const req = await IDKit.request(config).constraints(...);
  showQR(req.connectorURI);
  // after
  const req = await IDKit.requestWithInviteCode(config).constraints(...);
  showCode(req.code);

API surface added (mirrors existing URL-mode)

• Rust: BridgeConnection::create_for_invite_code with retry-once-on-409. BridgeConnection.invite_code() / .code_expires_at() accessors. New crypto.rs primitives: generate_invite_code, parse_invite_code, hkdf_invite_index_hex, hkdf_invite_key, generate_nonce.
• FFI: IDKitInviteCodeRequest sibling to IDKitRequestWrapper. New builder methods constraints_with_invite_code / preset_with_invite_code on IDKitBuilder.
• WASM: IDKitInviteCodeRequest sibling to IDKitRequest, same Rc<RefCell<Option<…>>> close semantics. constraintsWithInviteCode / presetWithInviteCode on the WASM builder.
• TypeScript: IDKitInviteCodeRequest interface + impl, IDKitInviteCodeBuilder, IDKit.requestWithInviteCode(...) entry point. Code mode is bridge-only by definition (user is on a different device than World App), so the builder skips the isInWorldApp() branch.
• React: IDKitInviteCodeRequestWidget, useIDKitInviteCodeRequest, useIDKitInviteCodeFlow hooks. New InviteCodeState UI component.
• Swift: presetWithInviteCode(_:) / constraintsWithInviteCode(_:) on the builder; IDKitInviteCodeRequest wrapper exposing code and expiresAt: Date.
• Examples: browser (vanilla), Next.js (React widget + mode toggle), iOS sample.

Tests

• 9 new Rust unit tests covering code generation, parser (round-trip, separator stripping, lowercase normalization, Crockford ambiguity collapse, U-rejection, length validation, check-digit validation, exhaustive single-char substitution detection across all positions × all alphabet chars), HKDF determinism, hex output shape, index/key differentiation across info strings.
• 86 existing Rust tests pass; 54 core JS tests pass; 23 React tests pass.
• Clippy clean on native + ffi feature combos.

Test plan

• Run the browser example (pnpm -C js/examples/browser dev); toggle "Use invite code" and confirm a 6-char code is rendered with countdown.
• Run the Next.js example (pnpm -C js/examples/nextjs dev); switch the demo toggle to invite-code and confirm the widget renders the code.
• Run the iOS sample, switch to invite-code mode, and confirm the code surfaces with the same expiry semantics.
• End-to-end: enter the code in World App on iOS (APP-9424), confirm proof completes and the RP poll loop resolves to Confirmed.
• Verify URL/QR-mode adopters compile and run unchanged (no header sent on GET /response/:id).

Dependencies

• wallet-bridge APP-9425 must be deployed for the code path to function. The session_nonce enforcement on GET /response/:id is a release-blocking follow-up on the Bridge side (currently stored but not verified — see spec §10).
• world-app-ios APP-9424 ships the WalletBridgeInviteCodeRedeemer that decrypts the /code/redeem payload and runs the iOS Selfie Check flow.

🤖 Generated with Claude Code

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