[backport] [world-vercel] Use stream control frame for transparent reconnection#1766
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VaguelySerious merged 5 commits intostablefrom Apr 16, 2026
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[backport] [world-vercel] Use stream control frame for transparent reconnection#1766VaguelySerious merged 5 commits intostablefrom
VaguelySerious merged 5 commits intostablefrom
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Add hold-back buffer to readFromStream that detects the 13-byte stream control frame appended by workflow-server on timeout. When the server signals a timeout (done=false), the client transparently reconnects from the next chunk index. Caps reconnections at 50 (~100 min). Network errors propagate to consumers via controller.error() instead of silently closing. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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🦋 Changeset detectedLatest commit: d78a4d4 The changes in this PR will be included in the next version bump. This PR includes changesets to release 18 packages
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🧪 E2E Test Results❌ Some tests failed Summary
❌ Failed Tests▲ Vercel Production (12 failed)astro (1 failed):
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hono (1 failed):
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nextjs-webpack (3 failed):
sveltekit (1 failed):
vite (2 failed):
🌍 Community Worlds (68 failed)mongodb-dev (1 failed):
redis-dev (1 failed):
turso-dev (1 failed):
turso (65 failed):
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The code itself is a clean backport of the reconnection logic from #1742, but there's a fundamental protocol mismatch that makes it non-functional.
Re: why not use the backport Action: The repo has a Backport to stable workflow (.github/workflows/backport.yml) that triggers on merged PRs with the backport-stable label. PR #1742 has no labels and hasn't been merged yet, so the action was never triggered. Once #1742 is merged with the backport-stable label, the action would cherry-pick it automatically (or use OpenCode to resolve conflicts if the cherry-pick fails). That said, cherry-picking #1742 would have the same protocol mismatch described below, so a manual backport with adaptation is the right call — it just needs a different approach to signal control frame support.
Changes reviewed:
parseStreamControlFrame,concatUint8Arrays,STREAM_CONTROL_FRAME_SIZE— identical to main, correct.- Hold-back buffer + reconnection loop in
readFromStream— identical logic to main'sstreams.get, withMAX_RECONNECTS=50andcontroller.error(err)on network errors. All good. - Unit tests for
parseStreamControlFrame— identical to main, 8 tests. Good. - Integration tests for reconnection — 3 tests (reconnect, backward compat, error propagation). Good coverage.
- Changeset — correct.
| }); | ||
| if (!response.ok) { | ||
| throw new Error(`Failed to fetch stream: ${response.status}`); | ||
| } |
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Blocking: ?controlFrame=1 is not supported by workflow-server. The server decides whether to emit the control frame based solely on the API version from the URL path:
// workflow-server/lib/handlers/stream.ts:420
const enableControlFrame = getApiVersion(req) >= 3;getApiVersion() is set by the v3 Hono sub-app middleware when the request path starts with /api/v3/. A query parameter has no effect.
On main, PR #1742 solved this by switching getStreamUrl to use /v3/runs/:runId/stream/:name. But on stable, readFromStream uses the deprecated route /v2/stream/:name (no runId), and the v3 API doesn't register that deprecated route — only /v3/runs/:runId/stream/:streamId exists.
So the control frame will never be emitted for this code path, and the reconnection logic is dead code.
Options to fix:
- If
readFromStreamonstablehas access to arunIdsomewhere (even via a different caller), thread it through and use/v3/runs/:runId/stream/:name - Add server-side support for
?controlFrame=1on the v2 deprecated stream route (a small change ingetStreamHandler) - Register the deprecated
/stream/:streamIdroute on the v3 sub-app inapp.ts(one line)
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Fixed in 8781b5f — switched to /v3/stream/:name (option 3). Companion server PR: vercel/workflow-server#387 registers the deprecated stream route on the v3 sub-app.
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I suppose you did a "manual" backport because the World API is different on |
The server enables control frames based on API version (v3+), not a query param. Use the v3 deprecated stream route which will be registered on the server via vercel/workflow-server#387. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Co-authored-by: vercel[bot] <35613825+vercel[bot]@users.noreply.github.com> Signed-off-by: Peter Wielander <mittgfu@gmail.com>
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… with streaming hold-back buffer Re-applies #1742's reconnect feature on stable, without the arrayBuffer() rewrite that shipped in 4.2.3 (#1766) and defeated incremental streaming. - readFromStream returns the ReadableStream promptly; a hold-back buffer inside the pull loop holds only the last 13 bytes, forwarding surplus bytes as they arrive. This preserves incremental delivery for AI UIs. - On upstream close, the tail is parsed for a stream control frame (done=true → close; done=false → reconnect from nextIndex; no frame → forward tail as data for older servers). - Network errors propagate via controller.error() rather than silent close. - Caps reconnections at 50 (~100 min of streaming at 2-min server timeout). Adds a regression test that asserts data reaches the consumer before upstream close — any buffer-then-replay implementation fails it. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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… with streaming hold-back buffer Re-applies #1742's reconnect feature on stable, without the arrayBuffer() rewrite that shipped in 4.2.3 (#1766) and defeated incremental streaming. - readFromStream returns the ReadableStream promptly; a hold-back buffer inside the pull loop holds only the last 13 bytes, forwarding surplus bytes as they arrive. This preserves incremental delivery for AI UIs. - On upstream close, the tail is parsed for a stream control frame (done=true → close; done=false → reconnect from nextIndex; no frame → forward tail as data for older servers). - Network errors propagate via controller.error() rather than silent close. - Caps reconnections at 50 (~100 min of streaming at 2-min server timeout). Adds a regression test that asserts data reaches the consumer before upstream close — any buffer-then-replay implementation fails it. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> Signed-off-by: Peter Wielander <mittgfu@gmail.com>
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Summary
Backport of #1742 to
stable.readFromStreamthat detects the 13-byte stream control frame appended by workflow-server on timeoutdone=false), the client transparently reconnects from the next chunk index using?controlFrame=1controller.error()instead of silently closingTest plan
parseStreamControlFrame(8 tests)🤖 Generated with Claude Code