feat(files): @shade/files 0.3.0 — E2EE filesystem RPC primitive

M-Files-1..6 land the full files-RPC layer + everything 0.3.0 needs to
ship. Apps keep their own UI; this layer ships the typed RPC, the
streams bridge for content I/O, and production hooks (rate limit,
retention, fingerprint gate, metrics).

@shade/files (NEW)
- Standard ops: list/stat/mkdir/delete/move/read/write/getThumbnail with
  Zod-validated wire schemas + clean user-handler types.
- Custom ops: typed via TypeScript declaration merging on CustomOpsMap
  + per-op Zod schemas; client.custom('app.foo', {...}) is fully typed.
- Content I/O: inline (≤ 256 KiB plaintext) base64-in-RPC; streams
  (> 256 KiB) ride @shade/transfer via userMetadata.shadeFilesWriteId
  / shadeFilesReadStreamId correlation. Server-side TransformStream
  bridges accept inbound transfers immediately (engine rejects chunks
  that arrive before accept) and park the readable for the matching
  RPC.
- Directory ops: walk(path, opts) async-iterable depth-first walker;
  uploadDirectory()/downloadDirectory() with bounded concurrency pool
  (default 4, cap 16), aggregated progress, abort.
- Production hooks (callback-based, vendor-neutral): rate-limit (op +
  byte), idempotency cache (LRU + TTL + in-flight de-dupe), path
  policy (traversal + percent-decode hardening), fingerprint gate
  (required/optional/reject), pluggable Ed25519 sig verification with
  ±5 min replay window, onMetric sink (standard names).
- React hooks (subpath @shade/files/react): ShadeFilesProvider,
  useShadeFiles, useFileList, useFileTransfer/Upload/Download.
- Shade.files.serve(handler) + Shade.files.client(peer) high-level
  entrypoint in @shade/sdk; lazy + memoized; one handler per Shade.

Wire format bump
- @shade/proto wire VERSION 0x01 → 0x02. Length prefixes changed from
  u16 to u32. The previous u16 silently truncated payloads above
  64 KiB — a hard correctness ceiling that blocked inline file ops
  up to 256 KiB. Wire-incompatible with 0.2.x peers; new sessions
  only. Cross-platform Kotlin port (android/shade-android) updated to
  match; test-vectors/wire-format.json regenerated.

Concurrency safety
- ShadeSessionManager.encrypt/.decrypt now run under per-peer mutex.
  Concurrent decryptions of the same peer raced ratchet state
  (manifested as sporadic "Failed to decrypt — wrong key or tampered
  data" under load — surfaced once concurrent uploadDirectory pumped
  many writes in flight). Encrypt was already serialized via
  Shade.send's encryptChains; decrypt is now serialized at the
  manager layer too.

@shade/streams extension
- StreamMetadata.userMetadata?: Record<string, string> for
  application-level key/value pairs that round-trip verbatim through
  stream-init plaintext. Used by @shade/files for write/read
  correlation; available to any consumer.

@shade/sdk extension
- Shade.files getter (lazy + memoized).
- BackgroundHooks.onPruneFiles + periodic timer (default 5 min) +
  BackgroundTasks.setHook(name, fn) for runtime hook registration.

Bundles in-flight 0.2.0 work
- packages/shade-streams/, packages/shade-transfer/, related
  shade-sdk streams-bridge + shade-widgets transfer hooks were
  uncommitted prior to this session. Including them keeps the
  workspace consistent at 0.3.0 since @shade/files depends on them.

Tests
- 74 new tests in @shade/files (572 → 646 workspace pass; 0 fail;
  3× stable). Coverage spans unit (inline-threshold + concurrency),
  integration (read-write inline + streams up to 1 MiB, walk +
  upload/download directory, custom-op, metrics, SDK namespace
  end-to-end), and security (tampered-envelope sig verification,
  replay window, fingerprint gate, rate-limit + quota).

Release artifacts
- All packages bumped to 0.3.0 via scripts/bump-version.ts.
- scripts/publish-all.ts PACKAGES updated with shade-files in
  topological order (after shade-transfer, before shade-sdk).
- bun run publish:dry clean (14 packed, 0 failed).
- examples/08-files-browser/ — three-process CLI demo (prekey + Bob
  server + Alice CLI) covering list/stat/mkdir/delete/upload/download.
- docs/files.md — full API + design doc.
- CHANGELOG.md 0.3.0 entry.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/shade-transfer/tests/http-roundtrip.test.ts

@@ -0,0 +1,204 @@
+import { describe, test, expect, afterAll } from 'bun:test';
+import { SubtleCryptoProvider } from '@shade/crypto-web';
+import { sha256Once } from '@shade/streams';
+import {
+  TransferEngine,
+  MemoryControlChannel,
+  ShadeTransferHttpTransport,
+  createTransferRoutes,
+  type TransferHandle,
+  type TransferResult,
+} from '../src/index.js';
+
+const crypto = new SubtleCryptoProvider();
+
+function hex(bytes: Uint8Array): string {
+  return Array.from(bytes, (b) => b.toString(16).padStart(2, '0')).join('');
+}
+
+interface IntegrationServers {
+  baseUrl: string;
+  senderEngine: TransferEngine;
+  receiverEngine: TransferEngine;
+  serverHandle: { stop: () => void };
+}
+
+const cleanups: Array<() => void> = [];
+
+afterAll(() => {
+  for (const c of cleanups) c();
+});
+
+async function setup(): Promise<IntegrationServers> {
+  const { a: ctrlA, b: ctrlB } = MemoryControlChannel.linked('alice', 'bob');
+
+  const receiverEngine = new TransferEngine({
+    crypto,
+    controlChannel: ctrlB,
+    transport: {
+      // Receiver-side transport is unused for outgoing operations; we only
+      // route incoming chunks via the Hono server.
+      probe: async () => undefined,
+      sendChunk: async () => {
+        throw new Error('receiver-side sendChunk should not be called');
+      },
+      fetchResumeState: async () => null,
+    },
+    myAddress: 'bob',
+  });
+
+  // Spin up a Hono+Bun server that routes chunks into receiverEngine.
+  const app = await createTransferRoutes(receiverEngine);
+  // Bun's `Bun.serve` accepts a Hono app's `fetch` handler.
+  const bunGlobal = (globalThis as unknown as { Bun?: { serve: (opts: unknown) => { url: URL; stop: () => void } } }).Bun;
+  if (bunGlobal === undefined) throw new Error('Bun runtime required for this test');
+  const server = bunGlobal.serve({
+    port: 0,
+    fetch: (req: Request) => app.fetch(req),
+  });
+  const baseUrl = server.url.toString().replace(/\/$/, '');
+
+  const senderEngine = new TransferEngine({
+    crypto,
+    controlChannel: ctrlA,
+    transport: new ShadeTransferHttpTransport({
+      resolveBaseUrl: async () => baseUrl,
+      authenticator: {
+        signChunk: async () => ({ 'X-Shade-Sender-Address': 'alice' }),
+        signControl: async () => ({ 'X-Shade-Sender-Address': 'alice' }),
+      },
+    }),
+    myAddress: 'alice',
+  });
+
+  cleanups.push(() => {
+    server.stop();
+    senderEngine.destroy();
+    receiverEngine.destroy();
+  });
+
+  return { baseUrl, senderEngine, receiverEngine, serverHandle: server };
+}
+
+async function uploadRoundtrip(
+  servers: IntegrationServers,
+  input: Uint8Array,
+  opts?: { lanes?: number; chunkSize?: number; partition?: 'auto' | 'range' | 'round-robin' },
+): Promise<{ senderResult: TransferResult; received: Uint8Array }> {
+  let resolveRecv!: (h: TransferHandle) => void;
+  const recvHandlePromise = new Promise<TransferHandle>((r) => {
+    resolveRecv = r;
+  });
+  const unsubscribe = servers.receiverEngine.onIncomingTransfer(async (incoming) => {
+    const h = await incoming.accept({ output: { kind: 'buffer' } });
+    resolveRecv(h);
+  });
+
+  const handle = await servers.senderEngine.upload({
+    to: 'bob',
+    input,
+    ...(opts?.lanes !== undefined ? { lanes: opts.lanes } : {}),
+    ...(opts?.chunkSize !== undefined ? { chunkSize: opts.chunkSize } : {}),
+    ...(opts?.partition !== undefined ? { partition: opts.partition } : {}),
+    metadata: { name: 'http-test.bin' },
+  });
+  const recvHandle = await recvHandlePromise;
+  const [senderResult, recvResult] = await Promise.all([handle.done(), recvHandle.done()]);
+  unsubscribe();
+  const received =
+    (recvResult as TransferResult & { bytes?: Uint8Array }).bytes ?? new Uint8Array();
+  return { senderResult, received };
+}
+
+describe('HTTP transport — Bun.serve loopback', () => {
+  test('100 KiB / 1 lane', async () => {
+    const servers = await setup();
+    const input = crypto.randomBytes(100 * 1024);
+    const { senderResult, received } = await uploadRoundtrip(servers, input, {
+      lanes: 1,
+      chunkSize: 32 * 1024,
+    });
+    expect(received).toEqual(input);
+    expect(senderResult.sha256).toBe(hex(sha256Once(input)));
+    expect(senderResult.bytesSent).toBe(input.length);
+  });
+
+  test('1 MiB / 4 lanes range', async () => {
+    const servers = await setup();
+    const input = crypto.randomBytes(1024 * 1024);
+    const { senderResult, received } = await uploadRoundtrip(servers, input, {
+      lanes: 4,
+      chunkSize: 64 * 1024,
+      partition: 'range',
+    });
+    expect(received).toEqual(input);
+    expect(senderResult.sha256).toBe(hex(sha256Once(input)));
+  });
+
+  test('1 MiB / 4 lanes round-robin', async () => {
+    const servers = await setup();
+    const input = crypto.randomBytes(1024 * 1024);
+    const { senderResult, received } = await uploadRoundtrip(servers, input, {
+      lanes: 4,
+      chunkSize: 64 * 1024,
+      partition: 'round-robin',
+    });
+    expect(received).toEqual(input);
+    expect(senderResult.sha256).toBe(hex(sha256Once(input)));
+  });
+
+  test(
+    '8 MiB / 4 lanes range (ship-gate proxy for 100 MB)',
+    async () => {
+      const servers = await setup();
+      const input = crypto.randomBytes(8 * 1024 * 1024);
+      const { senderResult, received } = await uploadRoundtrip(servers, input, {
+        lanes: 4,
+        chunkSize: 256 * 1024,
+        partition: 'range',
+      });
+      expect(received).toEqual(input);
+      expect(senderResult.sha256).toBe(hex(sha256Once(input)));
+    },
+    30_000,
+  );
+
+  test('upload with ReadableStream input — round-robin auto-pick', async () => {
+    const servers = await setup();
+    const input = crypto.randomBytes(512 * 1024);
+    const stream = new ReadableStream<Uint8Array>({
+      start(controller) {
+        for (let off = 0; off < input.length; off += 32 * 1024) {
+          controller.enqueue(input.subarray(off, Math.min(off + 32 * 1024, input.length)));
+        }
+        controller.close();
+      },
+    });
+    const { senderResult, received } = await uploadRoundtrip(servers, stream as unknown as Uint8Array, {
+      lanes: 4,
+      chunkSize: 32 * 1024,
+    });
+    expect(received).toEqual(input);
+    expect(senderResult.sha256).toBe(hex(sha256Once(input)));
+  });
+
+  test('peer offline → TransferOfflineError', async () => {
+    const { a: ctrlA } = MemoryControlChannel.linked('alice', 'bob');
+    const sender = new TransferEngine({
+      crypto,
+      controlChannel: ctrlA,
+      transport: new ShadeTransferHttpTransport({
+        resolveBaseUrl: async () => 'http://127.0.0.1:1', // intentionally unreachable
+      }),
+      myAddress: 'alice',
+    });
+    cleanups.push(() => sender.destroy());
+
+    await expect(
+      sender.upload({
+        to: 'bob',
+        input: crypto.randomBytes(64),
+      }),
+    ).rejects.toThrow(/offline|fetch failed|connection|ECONN|connect/i);
+  });
+});

packages/shade-transfer/tests/memory-roundtrip.test.ts

@@ -0,0 +1,193 @@
+import { describe, test, expect } from 'bun:test';
+import { SubtleCryptoProvider } from '@shade/crypto-web';
+import { sha256Once } from '@shade/streams';
+import {
+  TransferEngine,
+  MemoryControlChannel,
+  MemoryTransferTransport,
+} from '../src/index.js';
+import type { IncomingTransfer, TransferResult } from '../src/index.js';
+
+const crypto = new SubtleCryptoProvider();
+
+function hex(bytes: Uint8Array): string {
+  return Array.from(bytes, (b) => b.toString(16).padStart(2, '0')).join('');
+}
+
+interface PairedEngines {
+  sender: TransferEngine;
+  receiver: TransferEngine;
+}
+
+function makePair(): PairedEngines {
+  const { a: ctrlA, b: ctrlB } = MemoryControlChannel.linked('alice', 'bob');
+  const { a: txA, b: txB } = MemoryTransferTransport.linked('alice', 'bob');
+
+  const senderEngine = new TransferEngine({
+    crypto,
+    controlChannel: ctrlA,
+    transport: txA,
+    myAddress: 'alice',
+  });
+  const receiverEngine = new TransferEngine({
+    crypto,
+    controlChannel: ctrlB,
+    transport: txB,
+    myAddress: 'bob',
+  });
+
+  // Wire receiver-side transport to route chunks into receiver-engine.
+  txB.setChunkHandler(async (from, streamId, laneId, seq, bytes) =>
+    receiverEngine.receiveChunk(from, streamId, laneId, seq, bytes),
+  );
+  txB.setResumeProvider(async (from, streamId) =>
+    receiverEngine.getResumeState(from, streamId),
+  );
+
+  return { sender: senderEngine, receiver: receiverEngine };
+}
+
+async function uploadAndAwait(
+  pair: PairedEngines,
+  input: Uint8Array,
+  opts?: { lanes?: number; chunkSize?: number; partition?: 'auto' | 'range' | 'round-robin' },
+): Promise<{ result: TransferResult; received: Uint8Array }> {
+  // The handler accepts and PUBLISHES the receive-handle out-of-band so
+  // it can return promptly (control channel awaits handler completion).
+  let resolveReceiveHandle!: (h: import('../src/index.js').TransferHandle) => void;
+  const receiveHandlePromise = new Promise<import('../src/index.js').TransferHandle>(
+    (r) => { resolveReceiveHandle = r; },
+  );
+  const unsubscribe = pair.receiver.onIncomingTransfer(async (incoming: IncomingTransfer) => {
+    const handle = await incoming.accept({ output: { kind: 'buffer' } });
+    resolveReceiveHandle(handle);
+  });
+
+  const handle = await pair.sender.upload({
+    to: 'bob',
+    input,
+    ...(opts?.lanes !== undefined ? { lanes: opts.lanes } : {}),
+    ...(opts?.chunkSize !== undefined ? { chunkSize: opts.chunkSize } : {}),
+    ...(opts?.partition !== undefined ? { partition: opts.partition } : {}),
+    metadata: { name: 'test.bin', contentType: 'application/octet-stream' },
+  });
+  const recvHandle = await receiveHandlePromise;
+  const [senderResult, receiverResult] = await Promise.all([handle.done(), recvHandle.done()]);
+  unsubscribe();
+  const bytes =
+    (receiverResult as TransferResult & { bytes?: Uint8Array }).bytes ?? new Uint8Array(0);
+  return { result: senderResult, received: bytes };
+}
+
+describe('TransferEngine (memory loopback)', () => {
+  test('1 KiB upload — 1 lane (auto-degrade for small file)', async () => {
+    const pair = makePair();
+    const input = crypto.randomBytes(1024);
+    const { result, received } = await uploadAndAwait(pair, input, { lanes: 4, chunkSize: 256 });
+    expect(received).toEqual(input);
+    expect(result.sha256).toBe(hex(sha256Once(input)));
+  });
+
+  test('256 KiB upload — 4 lanes range partition', async () => {
+    const pair = makePair();
+    const input = crypto.randomBytes(256 * 1024);
+    const { result, received } = await uploadAndAwait(pair, input, {
+      lanes: 4,
+      chunkSize: 16 * 1024,
+      partition: 'range',
+    });
+    expect(received).toEqual(input);
+    expect(result.sha256).toBe(hex(sha256Once(input)));
+  });
+
+  test('1 MiB upload — 4 lanes round-robin partition', async () => {
+    const pair = makePair();
+    const input = crypto.randomBytes(1024 * 1024);
+    const { result, received } = await uploadAndAwait(pair, input, {
+      lanes: 4,
+      chunkSize: 64 * 1024,
+      partition: 'round-robin',
+    });
+    expect(received).toEqual(input);
+    expect(result.sha256).toBe(hex(sha256Once(input)));
+  });
+
+  test('integrity: same sha256 across lane counts', async () => {
+    const input = crypto.randomBytes(512 * 1024);
+    const expected = hex(sha256Once(input));
+    for (const lanes of [1, 2, 4, 8]) {
+      const pair = makePair();
+      const { result, received } = await uploadAndAwait(pair, input, { lanes, chunkSize: 8 * 1024 });
+      expect(received).toEqual(input);
+      expect(result.sha256).toBe(expected);
+    }
+  });
+
+  test('upload with ReadableStream input → round-robin partition', async () => {
+    const pair = makePair();
+    const input = crypto.randomBytes(300 * 1024);
+    const stream = new ReadableStream<Uint8Array>({
+      start(controller) {
+        for (let off = 0; off < input.length; off += 64 * 1024) {
+          controller.enqueue(input.subarray(off, Math.min(off + 64 * 1024, input.length)));
+        }
+        controller.close();
+      },
+    });
+    let resolveRecv!: (h: import('../src/index.js').TransferHandle) => void;
+    const recvHandlePromise = new Promise<import('../src/index.js').TransferHandle>((r) => {
+      resolveRecv = r;
+    });
+    const unsubscribe = pair.receiver.onIncomingTransfer(async (incoming) => {
+      const h = await incoming.accept({ output: { kind: 'buffer' } });
+      resolveRecv(h);
+    });
+    const handle = await pair.sender.upload({
+      to: 'bob',
+      input: stream,
+      lanes: 4,
+      chunkSize: 32 * 1024,
+    });
+    const recvHandle = await recvHandlePromise;
+    const [, recvResult] = await Promise.all([handle.done(), recvHandle.done()]);
+    unsubscribe();
+    const bytes = (recvResult as TransferResult & { bytes?: Uint8Array }).bytes ?? new Uint8Array();
+    expect(bytes).toEqual(input);
+  });
+
+  test('progress events fire and end with complete', async () => {
+    const pair = makePair();
+    const input = crypto.randomBytes(64 * 1024);
+    const senderProgressSamples: number[] = [];
+    const receiverEvents: string[] = [];
+
+    let resolveRecv!: (h: import('../src/index.js').TransferHandle) => void;
+    const recvHandlePromise = new Promise<import('../src/index.js').TransferHandle>((r) => {
+      resolveRecv = r;
+    });
+    const unsub = pair.receiver.onIncomingTransfer(async (incoming) => {
+      const h = await incoming.accept({
+        output: { kind: 'buffer' },
+        onEvent: (e) => {
+          receiverEvents.push(e.type);
+        },
+      });
+      resolveRecv(h);
+    });
+
+    const handle = await pair.sender.upload({
+      to: 'bob',
+      input,
+      lanes: 2,
+      chunkSize: 8 * 1024,
+      onProgress: (p) => senderProgressSamples.push(p.bytesSent),
+    });
+    const recvHandle = await recvHandlePromise;
+    await Promise.all([handle.done(), recvHandle.done()]);
+    unsub();
+    expect(senderProgressSamples.length).toBeGreaterThan(0);
+    expect(senderProgressSamples[senderProgressSamples.length - 1]).toBe(64 * 1024);
+    expect(receiverEvents).toContain('start');
+    expect(receiverEvents).toContain('complete');
+  });
+});

packages/shade-transfer/tests/resume.test.ts

@@ -0,0 +1,152 @@
+import { describe, test, expect } from 'bun:test';
+import { SubtleCryptoProvider } from '@shade/crypto-web';
+import { sha256Once } from '@shade/streams';
+import {
+  TransferEngine,
+  MemoryControlChannel,
+  MemoryResumeStore,
+  ShadeTransferHttpTransport,
+  createTransferRoutes,
+  type TransferHandle,
+  type TransferResult,
+} from '../src/index.js';
+
+const crypto = new SubtleCryptoProvider();
+
+function hex(b: Uint8Array): string {
+  return Array.from(b, (x) => x.toString(16).padStart(2, '0')).join('');
+}
+
+describe('Resume protocol — kill-restart-verify', () => {
+  test('sender crash mid-transfer → resumeUpload completes the same stream', async () => {
+    const senderResumeStore = new MemoryResumeStore();
+    // Stable deviceKey shared across engine instances — simulates a stable
+    // identity-derived key. In real use this is `deriveDeviceKey(identity)`.
+    const deviceKey = crypto.randomBytes(32);
+
+    // Receiver is a single, long-lived engine. Its in-memory IncomingState
+    // already tracks accepted chunks; we don't need to persist receiver state
+    // for the in-process scenario.
+    const { a: ctrlA, b: ctrlB } = MemoryControlChannel.linked('alice', 'bob');
+    const receiverEngine = new TransferEngine({
+      crypto,
+      controlChannel: ctrlB,
+      transport: {
+        probe: async () => undefined,
+        sendChunk: async () => {
+          throw new Error('receiver-side sendChunk should not be called');
+        },
+        fetchResumeState: async () => null,
+      },
+      myAddress: 'bob',
+    });
+    const receiverApp = await createTransferRoutes(receiverEngine);
+    const port = 22000 + Math.floor(Math.random() * 500);
+    const server = Bun.serve({ port, fetch: receiverApp.fetch });
+    const baseUrl = `http://localhost:${port}`;
+
+    // Receiver accepts incoming.
+    let resolveRecv!: (h: TransferHandle) => void;
+    const recvHandlePromise = new Promise<TransferHandle>((r) => {
+      resolveRecv = r;
+    });
+    receiverEngine.onIncomingTransfer(async (incoming) => {
+      const h = await incoming.accept({ output: { kind: 'buffer' } });
+      resolveRecv(h);
+    });
+
+    // Sender #1 — this one will "crash" partway through.
+    const senderEngine1 = new TransferEngine({
+      crypto,
+      controlChannel: ctrlA,
+      transport: new ShadeTransferHttpTransport({
+        resolveBaseUrl: async () => baseUrl,
+        authenticator: {
+          signChunk: async () => ({ 'X-Shade-Sender-Address': 'alice' }),
+          signControl: async () => ({ 'X-Shade-Sender-Address': 'alice' }),
+        },
+      }),
+      myAddress: 'alice',
+      resumeStore: senderResumeStore,
+      deviceKey,
+    });
+
+    const input = crypto.randomBytes(256 * 1024); // 256 KiB
+
+    // Start an upload that will be intentionally interrupted. We pause the
+    // sender by aborting the upload after ~25% bytes. The receiver still
+    // holds its IncomingState — chunks already accepted stay tracked.
+    const abort = new AbortController();
+    let bytesAtAbort = 0;
+    const handle1 = await senderEngine1.upload({
+      to: 'bob',
+      input,
+      lanes: 4,
+      chunkSize: 8 * 1024,
+      partition: 'range',
+      signal: abort.signal,
+      onProgress: (p) => {
+        if (p.bytesSent > input.length / 4 && bytesAtAbort === 0) {
+          bytesAtAbort = p.bytesSent;
+          abort.abort();
+        }
+      },
+    });
+    const streamId = handle1.streamId;
+
+    // Wait for the upload to fail (abort).
+    let firstErrCaught = false;
+    try {
+      await handle1.done();
+    } catch {
+      firstErrCaught = true;
+    }
+    expect(firstErrCaught).toBe(true);
+    expect(bytesAtAbort).toBeGreaterThan(0);
+
+    // Tear down the first sender engine — simulates a crashed/restarted client.
+    senderEngine1.destroy();
+
+    // Sender #2 — fresh engine, same resume store.
+    const senderEngine2 = new TransferEngine({
+      crypto,
+      controlChannel: ctrlA, // re-use the link; in real life this would
+      transport: new ShadeTransferHttpTransport({
+        resolveBaseUrl: async () => baseUrl,
+        authenticator: {
+          signChunk: async () => ({ 'X-Shade-Sender-Address': 'alice' }),
+          signControl: async () => ({ 'X-Shade-Sender-Address': 'alice' }),
+        },
+      }),
+      myAddress: 'alice',
+      resumeStore: senderResumeStore,
+      deviceKey,
+    });
+
+    // Verify state is still in the resume store.
+    const persisted = await senderResumeStore.get(streamId);
+    expect(persisted).not.toBeNull();
+    expect(persisted!.status).toBe('active');
+
+    // Resume the upload with the same input bytes.
+    const handle2 = await senderEngine2.resumeUpload(streamId, input);
+    const senderResult = await handle2.done();
+    expect(senderResult.streamId).toBe(streamId);
+
+    // Receiver finishes too.
+    const recvHandle = await recvHandlePromise;
+    const recvResult = await recvHandle.done();
+    const received =
+      (recvResult as TransferResult & { bytes?: Uint8Array }).bytes ?? new Uint8Array();
+    expect(received).toEqual(input);
+    expect(senderResult.sha256).toBe(hex(sha256Once(input)));
+
+    // Persisted state should now be finished.
+    const after = await senderResumeStore.get(streamId);
+    expect(after?.status).toBe('finished');
+
+    senderEngine2.destroy();
+    receiverEngine.destroy();
+    server.stop();
+  }, 30_000);
+});

packages/shade-transfer/tests/ws-fallback.test.ts

@@ -0,0 +1,98 @@
+import { describe, test, expect, afterAll } from 'bun:test';
+import { SubtleCryptoProvider } from '@shade/crypto-web';
+import { sha256Once } from '@shade/streams';
+import {
+  TransferEngine,
+  MemoryControlChannel,
+  ShadeTransferHttpTransport,
+  ShadeTransferWsTransport,
+  FallbackTransferTransport,
+  createTransferRoutes,
+  type TransferHandle,
+  type TransferResult,
+} from '../src/index.js';
+
+const crypto = new SubtleCryptoProvider();
+
+function hex(b: Uint8Array): string {
+  return Array.from(b, (x) => x.toString(16).padStart(2, '0')).join('');
+}
+
+const cleanups: Array<() => void> = [];
+afterAll(() => {
+  for (const c of cleanups) c();
+});
+
+describe('WS opt-in transport with HTTP fallback', () => {
+  test('WS connect failure → falls back to HTTP transparently', async () => {
+    const { a: ctrlA, b: ctrlB } = MemoryControlChannel.linked('alice', 'bob');
+    const receiverEngine = new TransferEngine({
+      crypto,
+      controlChannel: ctrlB,
+      transport: {
+        probe: async () => undefined,
+        sendChunk: async () => {
+          throw new Error('not used');
+        },
+        fetchResumeState: async () => null,
+      },
+      myAddress: 'bob',
+    });
+    const httpApp = await createTransferRoutes(receiverEngine);
+    const httpPort = 23000 + Math.floor(Math.random() * 500);
+    const httpServer = Bun.serve({ port: httpPort, fetch: httpApp.fetch });
+    const httpBaseUrl = `http://localhost:${httpPort}`;
+    cleanups.push(() => httpServer.stop());
+
+    const ws = new ShadeTransferWsTransport({
+      // Resolve to a closed port — guaranteed connect failure.
+      resolveWsUrl: async () => `ws://127.0.0.1:1`,
+      connectTimeoutMs: 500,
+    });
+    const http = new ShadeTransferHttpTransport({
+      resolveBaseUrl: async () => httpBaseUrl,
+      authenticator: {
+        signChunk: async () => ({ 'X-Shade-Sender-Address': 'alice' }),
+        signControl: async () => ({ 'X-Shade-Sender-Address': 'alice' }),
+      },
+    });
+    const fallback = new FallbackTransferTransport(ws, http);
+
+    const senderEngine = new TransferEngine({
+      crypto,
+      controlChannel: ctrlA,
+      transport: fallback,
+      myAddress: 'alice',
+    });
+    cleanups.push(() => senderEngine.destroy());
+    cleanups.push(() => receiverEngine.destroy());
+
+    let resolveRecv!: (h: TransferHandle) => void;
+    const recvHandlePromise = new Promise<TransferHandle>((r) => {
+      resolveRecv = r;
+    });
+    receiverEngine.onIncomingTransfer(async (incoming) => {
+      const h = await incoming.accept({ output: { kind: 'buffer' } });
+      resolveRecv(h);
+    });
+
+    const input = crypto.randomBytes(64 * 1024);
+    const handle = await senderEngine.upload({
+      to: 'bob',
+      input,
+      lanes: 2,
+      chunkSize: 8 * 1024,
+    });
+    const recvHandle = await recvHandlePromise;
+    const [senderResult, recvResult] = await Promise.all([
+      handle.done(),
+      recvHandle.done(),
+    ]);
+
+    expect(fallback.fellBack).toBe(true);
+    const received =
+      (recvResult as TransferResult & { bytes?: Uint8Array }).bytes ?? new Uint8Array();
+    expect(received).toEqual(input);
+    expect(senderResult.sha256).toBe(hex(sha256Once(input)));
+  });
+});