fix(relay): keep bulk streaming from blocking client requests

Negotiate downstream delivery credit and schedule response streams fairly before encryption. Bound queued output, preserve deltas and WebSocket close ordering, and retain legacy peer compatibility.

Validated with 81 relay tests, workspace type-check and lint, web build and mobile assets, and slow-link tests through the production relay. Confirmed on LTE by the maintainer.

packages/web/server/lib/relay/cross-compat.test.js

@@ -12,16 +12,42 @@ import {
   decodeTunnelFrame as jsDecode,
   encodeFrameBatch as jsEncodeBatch,
   encodeTunnelFrame as jsEncode,
+  decodeDeliveryAck,
 } from './tunnel-codec.js';
 import {
   decodeFrameBatch as tsDecodeBatch,
   decodeTunnelFrame as tsDecode,
   encodeFrameBatch as tsEncodeBatch,
   encodeTunnelFrame as tsEncode,
+  encodeDeliveryAck,
 } from '../../../../ui/src/lib/relay/tunnel-codec.ts';
 import { TunnelFrameType as TsFrameType } from '../../../../ui/src/lib/relay/protocol.ts';
 
 describe('relay JS-host <-> TS-client cross compatibility', () => {
+  it('negotiates flow control independently of batching, with legacy fallback on either side', async () => {
+    const keys = await generateEcdhKeyPair();
+    const pub = await exportPublicKeyJwk(keys.publicKey);
+    for (const batch of [false, true]) {
+      for (const clientFlow of [false, true]) {
+        for (const hostFlow of [false, true]) {
+          const client = await createClientHandshake(pub, { batch, flowControl: clientFlow });
+          const host = createHostHandshake(keys.privateKey, { batch, flowControl: hostFlow });
+          const ready = await host.handleText(client.helloText);
+          const established = await client.handleText(ready.replyText);
+          expect(ready.flowControl).toBe(clientFlow && hostFlow);
+          expect(established.flowControl).toBe(clientFlow && hostFlow);
+          expect(established.batch).toBe(batch);
+          expect((await host.handleText(client.helloText)).text).toBe(ready.replyText);
+        }
+      }
+    }
+    expect(JsFrameType).toEqual(TsFrameType);
+    for (const bytes of [0, 8197, 2 ** 32 + 17, Number.MAX_SAFE_INTEGER]) {
+      expect(decodeDeliveryAck(encodeDeliveryAck(bytes))).toBe(bytes);
+    }
+    expect(() => decodeDeliveryAck(new Uint8Array(7))).toThrow();
+    expect(() => decodeDeliveryAck(new Uint8Array(8).fill(255))).toThrow();
+  });
   it('completes a handshake and exchanges frames both ways', async () => {
     const hostKeys = await generateEcdhKeyPair();
     const hostPubJwk = await exportPublicKeyJwk(hostKeys.publicKey);