release(v4.1.0): browser-friendly HTTP RPC for @shade/files

Default shade.files.client(peer) requires both peers to be mutually
addressable over HTTP — the response round-trips through
Shade.deliverControlEnvelope (POST to peer's /v1/transfer/control).
Browser tabs can't host an HTTP server, so they couldn't consume
@shade/files at all. Dispatch's filutforsker (admin-panel browser UI)
is the canonical use-case.

This release adds a parallel request-response transport: one POST per
RPC, encrypted envelope in the body, encrypted response in the same
HTTP response. No inbound channel needed on the client.

### New API

- shade.files.rpcRoute(opts?) — Hono app exposing POST /rpc.
- shade.files.httpClient(peer, opts) — request-response FileClient.
- FilesNamespace.serve(handler, { inlineOnly: true }) — skip streams-
  bridge (and its configureTransfers pre-condition); also skip
  channel-based dispatch so requests aren't double-dispatched.

### Limitations (v1)

Inline only (≤ 256 KiB). Streamed reads/writes throw clear errors
directing to shade.files.client(peer) on a server-to-server deploy.

### Tests

7 integration tests in tests/integration/http-rpc.test.ts covering
round-trip + negative cases (sender header, empty/garbage body,
maxBodyBytes, rpcRoute-without-serve).

### Symmetry

Mirrors @shade/server's shade-auth-middleware: encrypted envelope in
request body, decrypted via existing ratchet, response in same HTTP
roundtrip. No WebSocket, no SSE, no outbound from server.

Wire-compatible. Source-compatible. Lockstep bump to 4.1.0.

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

packages/shade-files/src/server/rpc-route.ts

@@ -0,0 +1,218 @@
+/**
+ * Request-response RPC route for `@shade/files`.
+ *
+ * Mounts a single `POST /rpc` Hono endpoint that accepts an encrypted
+ * `RpcRequest` envelope, dispatches it through the file handler, and
+ * returns the encrypted `RpcResponse` (or `RpcError`) envelope in the
+ * SAME HTTP response.
+ *
+ * This is the browser-friendly transport: the server never needs to
+ * make outbound calls back to the client, so a browser tab — which
+ * cannot host an HTTP server — can fully consume `@shade/files`.
+ *
+ * ### Wire contract
+ *
+ * Request:
+ * ```
+ * POST <mount>/rpc HTTP/1.1
+ * Content-Type: application/octet-stream
+ * X-Shade-Sender-Address: <peer address>
+ *
+ * <wire-encoded ShadeEnvelope (0x01 PreKeyMessage or 0x02 RatchetMessage)
+ *  containing JSON-encoded RpcRequest>
+ * ```
+ *
+ * Response (success):
+ * ```
+ * 200 OK
+ * Content-Type: application/octet-stream
+ *
+ * <wire-encoded ShadeEnvelope (0x02 RatchetMessage)
+ *  containing JSON-encoded RpcResponse | RpcError>
+ * ```
+ *
+ * Response (transport-level failure — no session, undecryptable, etc.):
+ * ```
+ * 4xx
+ * Content-Type: application/json
+ *
+ * { "error": "..." }
+ * ```
+ *
+ * ### Symmetry with shade-auth-middleware
+ *
+ * The shape mirrors `@shade/server`'s shade-auth-middleware: an
+ * encrypted envelope rides the request body, the server decrypts via
+ * the existing ratchet session, performs the protected operation,
+ * and returns an encrypted envelope in the response. No bidirectional
+ * channel required.
+ *
+ * @see {@link createFilesHttpClient} for the matching browser client.
+ */
+import { Hono } from 'hono';
+import { decodeEnvelope, encodeEnvelope } from '@shade/proto';
+import type { ShadeBridge } from '../integration/shade-bridge.js';
+import {
+  encodeEnvelope as encodeRpcEnvelope,
+  tryParseEnvelope,
+} from '../protocol/envelope-codec.js';
+import type { FileHandler } from './handler.js';
+import type { RpcError, RpcRequest, RpcResponse } from '../schemas/envelope.js';
+import { KIND_ERROR_V1 } from '../protocol/kinds.js';
+
+export interface FilesRpcRouteOptions {
+  /**
+   * Maximum request body size in bytes. Default 1 MiB. Inline payloads
+   * are capped at 256 KiB by the protocol; the headroom is for
+   * custom-op payloads and base64 inflation.
+   */
+  maxBodyBytes?: number;
+  /**
+   * Allow this server to accept the very first message (PreKeyMessage,
+   * `0x01`) over the RPC route. Disabled by default — most browser
+   * clients establish a session via `shade.initSessionFromBundle`
+   * before the first RPC. Enable when you want the RPC route to also
+   * be the X3DH carrier (uncommon but supported).
+   */
+  acceptFirstMessage?: boolean;
+}
+
+const DEFAULT_MAX_BODY_BYTES = 1 * 1024 * 1024;
+
+/**
+ * Build a Hono app with a single `POST /rpc` route. Mount under any
+ * base path: `app.route('/api/v1/shade-files', shade.files.rpcRoute())`.
+ *
+ * The `handler` must already be attached (typically via
+ * `shade.files.serve(handlerConfig)`); this route only ships the
+ * transport — it does not register a new file handler.
+ */
+export function createFilesRpcRoute(
+  shade: ShadeBridge,
+  handler: FileHandler,
+  options: FilesRpcRouteOptions = {},
+): Hono {
+  const maxBodyBytes = options.maxBodyBytes ?? DEFAULT_MAX_BODY_BYTES;
+  const app = new Hono();
+
+  app.post('/rpc', async (c) => {
+    const senderAddress = c.req.header('X-Shade-Sender-Address');
+    if (senderAddress === undefined || senderAddress === '') {
+      return c.json({ error: 'missing X-Shade-Sender-Address header' }, 400);
+    }
+
+    const contentLengthHeader = c.req.header('Content-Length');
+    if (contentLengthHeader !== undefined) {
+      const contentLength = Number.parseInt(contentLengthHeader, 10);
+      if (Number.isFinite(contentLength) && contentLength > maxBodyBytes) {
+        return c.json(
+          { error: `body exceeds maxBodyBytes (${contentLength} > ${maxBodyBytes})` },
+          413,
+        );
+      }
+    }
+
+    let bodyBytes: Uint8Array;
+    try {
+      const ab = await c.req.arrayBuffer();
+      if (ab.byteLength > maxBodyBytes) {
+        return c.json(
+          { error: `body exceeds maxBodyBytes (${ab.byteLength} > ${maxBodyBytes})` },
+          413,
+        );
+      }
+      bodyBytes = new Uint8Array(ab);
+    } catch (err) {
+      return c.json({ error: `failed to read request body: ${(err as Error).message}` }, 400);
+    }
+
+    if (bodyBytes.byteLength === 0) {
+      return c.json({ error: 'empty request body' }, 400);
+    }
+
+    // Decode the wire envelope. `decodeEnvelope` handles both `0x01`
+    // PreKeyMessage and `0x02` RatchetMessage shapes.
+    let plaintext: string;
+    try {
+      const envelope = decodeEnvelope(bodyBytes);
+      // First-message gate: only allow `prekey` envelopes when the
+      // operator has explicitly opted in.
+      if (options.acceptFirstMessage !== true && envelope.type === 'prekey') {
+        return c.json(
+          {
+            error:
+              'PreKeyMessage envelopes are not accepted on this RPC route — establish the session first via shade.initSessionFromBundle, or set acceptFirstMessage: true',
+          },
+          400,
+        );
+      }
+      plaintext = await shade.receive(senderAddress, envelope);
+    } catch (err) {
+      // Decryption failure — could be no session, corrupted envelope,
+      // or sender address mismatch. Treat as 401 since the envelope is
+      // self-authenticating: a valid sender would decrypt cleanly.
+      return c.json({ error: `decrypt failed: ${(err as Error).message}` }, 401);
+    }
+
+    // Parse the plaintext as an RpcRequest.
+    const classified = tryParseEnvelope(plaintext);
+    if (classified === null) {
+      return c.json({ error: 'plaintext is not a valid @shade/files envelope' }, 400);
+    }
+    if (classified.kind !== 'request') {
+      // Cancel envelopes are silently dropped — RPC route is request/
+      // response only. Cancellation across HTTP is achieved via
+      // AbortController on the client side, not protocol-level.
+      if (classified.kind === 'cancel') {
+        handler.handleCancel(senderAddress, classified.envelope);
+        // No response body — the cancel was best-effort.
+        return new Response(null, { status: 204 });
+      }
+      return c.json(
+        { error: `unexpected envelope kind on RPC route: ${classified.kind}` },
+        400,
+      );
+    }
+
+    const request: RpcRequest = classified.envelope;
+
+    // Dispatch through the file handler.
+    let result: RpcResponse | RpcError;
+    try {
+      result = await handler.handleRequest(senderAddress, request);
+    } catch (err) {
+      // Should never happen — handler.handleRequest catches its own
+      // errors and returns RpcError. If it didn't, that's a bug; emit
+      // a generic transport-level RpcError so the client can surface
+      // it deterministically.
+      result = {
+        kind: KIND_ERROR_V1,
+        id: request.id,
+        error: {
+          code: 'INTERNAL',
+          message: `handler raised: ${(err as Error).message}`,
+        },
+      };
+    }
+
+    // Encrypt the response and return it as wire bytes.
+    let responseBytes: Uint8Array;
+    try {
+      const responsePlaintext = encodeRpcEnvelope(result);
+      const responseEnvelope = await shade.send(senderAddress, responsePlaintext);
+      responseBytes = encodeEnvelope(responseEnvelope);
+    } catch (err) {
+      return c.json(
+        { error: `failed to encrypt response: ${(err as Error).message}` },
+        500,
+      );
+    }
+
+    return new Response(new Blob([responseBytes as unknown as ArrayBuffer]), {
+      status: 200,
+      headers: { 'Content-Type': 'application/octet-stream' },
+    });
+  });
+
+  return app;
+}