[world-vercel] Use stream control frame for transparent reconnection by VaguelySerious · Pull Request #1790 · vercel/workflow

VaguelySerious · 2026-04-17T00:26:29Z

Summary

Re-applies #1742's reconnect feature on `stable` — without the `arrayBuffer()` rewrite that shipped in 4.2.3 (#1766) and broke incremental streaming on Vercel (content only arrived on stream close). #1766 was reverted on `stable` (#1788, released as 4.2.4).

Root cause of the 4.2.3 regression: `await response.arrayBuffer()` inside `readFromStream` drained the upstream before returning the `ReadableStream`, so `run.getReadable()` blocked until the server closed the stream. The returned stream just replayed the already-complete buffer.

This PR restores the original hold-back buffer approach from #1742 (still in use on `main`), adapted to `stable`'s `readFromStream` signature.

What's in it

`readFromStream` returns the `ReadableStream` promptly. A hold-back buffer inside the pull loop keeps only the last 13 bytes (the control-frame size), forwarding surplus bytes as they arrive.
On upstream close, the tail is parsed:
- `done=true` → close cleanly
- `done=false` → reconnect from `nextIndex`
- no frame → forward tail as data (older-server backward compat)
Network errors propagate via `controller.error()` rather than a silent close.
Reconnections capped at 50 (~100 min of streaming at 2-min server timeout).
New regression test (`emits upstream bytes to the consumer before the stream closes`) asserts data flows before upstream EOF — any buffer-then-replay implementation fails it. This specifically catches the class of bug that shipped as 4.2.3.

Test plan

`pnpm vitest run` — 67/67 world-vercel tests pass (28 streamer + 11 reconnect parser + 28 other)
Reconnect + backward-compat + control-frame-split tests from [backport] [world-vercel] Use stream control frame for transparent reconnection #1766 still pass
New regression test fails if `readFromStream` is rewritten to drain upstream first
CI + auto-created workflow-server preview e2e
Manual validation against flight-booking-app once a preview tarball is available

Notes

Targets `stable` directly because `main` already carries [world-vercel] Use stream close control frame to decide whether to reconnect to stream #1742's hold-back implementation — this PR brings `stable` back into parity with reconnect support, on top of the 4.2.4 revert.
The pre-existing `writeToStream` typecheck error on `stable` (present on `origin/stable` before this branch) is untouched.

🤖 Generated with Claude Code

changeset-bot · 2026-04-17T00:26:34Z

🦋 Changeset detected

Latest commit: ee258dc

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 18 packages

Name	Type
@workflow/world-vercel	Patch
@workflow/cli	Patch
@workflow/core	Patch
@workflow/web	Patch
workflow	Patch
@workflow/world-testing	Patch
@workflow/builders	Patch
@workflow/next	Patch
@workflow/nitro	Patch
@workflow/vitest	Patch
@workflow/web-shared	Patch
@workflow/ai	Patch
@workflow/astro	Patch
@workflow/nest	Patch
@workflow/rollup	Patch
@workflow/sveltekit	Patch
@workflow/vite	Patch
@workflow/nuxt	Patch

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vercel · 2026-04-17T00:26:36Z

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Project	Deployment	Actions	Updated (UTC)
example-nextjs-workflow-turbopack	Ready	Preview, Comment	Apr 17, 2026 0:30am
example-nextjs-workflow-webpack	Ready	Preview, Comment	Apr 17, 2026 0:30am
example-workflow	Ready	Preview, Comment	Apr 17, 2026 0:30am
workbench-astro-workflow	Ready	Preview, Comment	Apr 17, 2026 0:30am
workbench-express-workflow	Ready	Preview, Comment	Apr 17, 2026 0:30am
workbench-fastify-workflow	Ready	Preview, Comment	Apr 17, 2026 0:30am
workbench-hono-workflow	Ready	Preview, Comment	Apr 17, 2026 0:30am
workbench-nitro-workflow	Ready	Preview, Comment	Apr 17, 2026 0:30am
workbench-nuxt-workflow	Ready	Preview, Comment	Apr 17, 2026 0:30am
workbench-sveltekit-workflow	Ready	Preview, Comment	Apr 17, 2026 0:30am
workbench-vite-workflow	Ready	Preview, Comment	Apr 17, 2026 0:30am
workflow-docs	Ready	Preview, Comment, Open in v0	Apr 17, 2026 0:30am
workflow-swc-playground	Ready	Preview, Comment	Apr 17, 2026 0:30am
workflow-web	Ready	Preview, Comment	Apr 17, 2026 0:30am

github-actions · 2026-04-17T00:26:41Z

🧪 E2E Test Results

❌ Some tests failed

Summary

	Passed	Failed	Skipped	Total
❌ ▲ Vercel Production	900	1	67	968
✅ 💻 Local Development	970	0	86	1056
✅ 📦 Local Production	970	0	86	1056
✅ 🐘 Local Postgres	970	0	86	1056
✅ 🪟 Windows	88	0	0	88
❌ 🌍 Community Worlds	139	83	0	222
✅ 📋 Other	246	0	18	264
Total	4283	84	343	4710

❌ Failed Tests

▲ Vercel Production (1 failed)

sveltekit (1 failed):

error handling catchability FatalError can be caught and detected with FatalError.is()

🌍 Community Worlds (83 failed)

mongodb (11 failed):

readableStreamWorkflow | wrun_01KPCDEV0N8PQBX7HQXBRBVS64
hookWorkflow is not resumable via public webhook endpoint | wrun_01KPCDFH1YQSFSVV015W1WK17T
webhookWorkflow | wrun_01KPCDFSP9DFEP41FPPJ2QYNP2
outputStreamWorkflow no startIndex (reads all chunks)
outputStreamWorkflow negative startIndex (reads from end)
outputStreamWorkflow - getTailIndex and getStreamChunks getTailIndex returns correct index after stream completes
outputStreamWorkflow - getTailIndex and getStreamChunks getTailIndex returns -1 before any chunks are written
outputStreamWorkflow - getTailIndex and getStreamChunks getStreamChunks returns same content as reading the stream
outputStreamInsideStepWorkflow - getWritable() called inside step functions | wrun_01KPCDJRHYBET9BD520MHYJQG7
concurrent hook token conflict - two workflows cannot use the same hook token simultaneously | wrun_01KPCDQ7X1M91F15KWCSG7H033
resilient start: addTenWorkflow completes when run_created returns 500 | wrun_01KPCDXEXGCXH0VHDT49AAHF97

redis (7 failed):

hookWorkflow is not resumable via public webhook endpoint | wrun_01KPCDFH1YQSFSVV015W1WK17T
outputStreamWorkflow negative startIndex (reads from end)
outputStreamWorkflow - getTailIndex and getStreamChunks getTailIndex returns correct index after stream completes
outputStreamWorkflow - getTailIndex and getStreamChunks getTailIndex returns -1 before any chunks are written
outputStreamWorkflow - getTailIndex and getStreamChunks getStreamChunks returns same content as reading the stream
concurrent hook token conflict - two workflows cannot use the same hook token simultaneously | wrun_01KPCDQ7X1M91F15KWCSG7H033
resilient start: addTenWorkflow completes when run_created returns 500 | wrun_01KPCDXEXGCXH0VHDT49AAHF97

turso (65 failed):

addTenWorkflow | wrun_01KPCDEB45HR5F1E88RVZK3JAE
addTenWorkflow | wrun_01KPCDEB45HR5F1E88RVZK3JAE
wellKnownAgentWorkflow (.well-known/agent) | wrun_01KPCDF08KKPWAQ7PVD2SKCJ78
should work with react rendering in step
promiseAllWorkflow | wrun_01KPCDEHJWP5ETJS19AG89D448
promiseRaceWorkflow | wrun_01KPCDEQ1GD6AXHKS1E2FZMER9
promiseAnyWorkflow | wrun_01KPCDES15ZVBHEQ419230WC22
importedStepOnlyWorkflow | wrun_01KPCDFDB96AA2827YQ3CD8AJD
readableStreamWorkflow | wrun_01KPCDEV0N8PQBX7HQXBRBVS64
hookWorkflow | wrun_01KPCDF5S02DMW2T56KA1W34G2
hookWorkflow is not resumable via public webhook endpoint | wrun_01KPCDFH1YQSFSVV015W1WK17T
webhookWorkflow | wrun_01KPCDFSP9DFEP41FPPJ2QYNP2
sleepingWorkflow | wrun_01KPCDFZ2DGN157PQ61KNDPAA3
parallelSleepWorkflow | wrun_01KPCDGB2FNK5G4XVQJ7GSZM8R
nullByteWorkflow | wrun_01KPCDGE8FE22NA1YJ1WFF6VBY
workflowAndStepMetadataWorkflow | wrun_01KPCDGGH4DQKZJZX552S74HRQ
outputStreamWorkflow no startIndex (reads all chunks)
outputStreamWorkflow positive startIndex (skips first chunk)
outputStreamWorkflow negative startIndex (reads from end)
outputStreamWorkflow - getTailIndex and getStreamChunks getTailIndex returns correct index after stream completes
outputStreamWorkflow - getTailIndex and getStreamChunks getTailIndex returns -1 before any chunks are written
outputStreamWorkflow - getTailIndex and getStreamChunks getStreamChunks returns same content as reading the stream
outputStreamInsideStepWorkflow - getWritable() called inside step functions | wrun_01KPCDJRHYBET9BD520MHYJQG7
fetchWorkflow | wrun_01KPCDK5ENNGNJHHMJC1RKW1NT
promiseRaceStressTestWorkflow | wrun_01KPCDK8P00SQXPD3707XAM87T
error handling error propagation workflow errors nested function calls preserve message and stack trace
error handling error propagation workflow errors cross-file imports preserve message and stack trace
error handling error propagation step errors basic step error preserves message and stack trace
error handling error propagation step errors cross-file step error preserves message and function names in stack
error handling retry behavior regular Error retries until success
error handling retry behavior FatalError fails immediately without retries
error handling retry behavior RetryableError respects custom retryAfter delay
error handling retry behavior maxRetries=0 disables retries
error handling catchability FatalError can be caught and detected with FatalError.is()
error handling not registered WorkflowNotRegisteredError fails the run when workflow does not exist
error handling not registered StepNotRegisteredError fails the step but workflow can catch it
error handling not registered StepNotRegisteredError fails the run when not caught in workflow
hookCleanupTestWorkflow - hook token reuse after workflow completion | wrun_01KPCDPM3JVFJVVH4SBXR892QP
concurrent hook token conflict - two workflows cannot use the same hook token simultaneously | wrun_01KPCDQ7X1M91F15KWCSG7H033
hookDisposeTestWorkflow - hook token reuse after explicit disposal while workflow still running | wrun_01KPCDQWKW6XF2NYGHMAD769N5
stepFunctionPassingWorkflow - step function references can be passed as arguments (without closure vars) | wrun_01KPCDRGBQGBX4PP2J61VG8MFW
stepFunctionWithClosureWorkflow - step function with closure variables passed as argument | wrun_01KPCDRRSK12SDD1NC9AF698RX
closureVariableWorkflow - nested step functions with closure variables | wrun_01KPCDRZ9C5MXV1S38E1EYN5BG
spawnWorkflowFromStepWorkflow - spawning a child workflow using start() inside a step | wrun_01KPCDS1EG8NXNNB1VYFR7246C
health check (queue-based) - workflow and step endpoints respond to health check messages
pathsAliasWorkflow - TypeScript path aliases resolve correctly | wrun_01KPCDSGJ3KQKHEHFAQ13QZCPF
Calculator.calculate - static workflow method using static step methods from another class | wrun_01KPCDSNXEVWHWXH3928ZG4X1T
AllInOneService.processNumber - static workflow method using sibling static step methods | wrun_01KPCDSW86T6BVEAKWY7EGFDV4
ChainableService.processWithThis - static step methods using this to reference the class | wrun_01KPCDT2MD8TR3WGMNYS0FKRCH
thisSerializationWorkflow - step function invoked with .call() and .apply() | wrun_01KPCDT8BW51BYHXX7QR5QZJ7G
customSerializationWorkflow - custom class serialization with WORKFLOW_SERIALIZE/WORKFLOW_DESERIALIZE | wrun_01KPCDTH53VT0AX0SWMD03EWA9
instanceMethodStepWorkflow - instance methods with "use step" directive | wrun_01KPCDTQK0WGZ0T10CH13Q2GZK
crossContextSerdeWorkflow - classes defined in step code are deserializable in workflow context | wrun_01KPCDV322NQVNK879EXAZ7AW4
stepFunctionAsStartArgWorkflow - step function reference passed as start() argument | wrun_01KPCDVAMGFBSHY0F50B9XRY6S
cancelRun - cancelling a running workflow | wrun_01KPCDVH3SYGSQWMH1V24W8DQ3
cancelRun via CLI - cancelling a running workflow | wrun_01KPCDVTNWAD8331GPPK683AWF
pages router addTenWorkflow via pages router
pages router promiseAllWorkflow via pages router
pages router sleepingWorkflow via pages router
hookWithSleepWorkflow - hook payloads delivered correctly with concurrent sleep | wrun_01KPCDW6J1SYGVPA6PZ0HVTMYF
sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_01KPCDWTJ0A2RBCBADY4TB6PZ7
sleepWithSequentialStepsWorkflow - sequential steps work with concurrent sleep (control) | wrun_01KPCDX4F3VP5DQDC942H624E4
importMetaUrlWorkflow - import.meta.url is available in step bundles | wrun_01KPCDXAT2MWN03RQDQCCVYB16
metadataFromHelperWorkflow - getWorkflowMetadata/getStepMetadata work from module-level helper (#1577) | wrun_01KPCDXCWM794ANQS89DT0VN2S
resilient start: addTenWorkflow completes when run_created returns 500 | wrun_01KPCDXEXGCXH0VHDT49AAHF97

Details by Category

❌ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro	81	0	7
✅ example	81	0	7
✅ express	81	0	7
✅ fastify	81	0	7
✅ hono	81	0	7
✅ nextjs-turbopack	86	0	2
✅ nextjs-webpack	86	0	2
✅ nitro	81	0	7
✅ nuxt	81	0	7
❌ sveltekit	80	1	7
✅ vite	81	0	7

✅ 💻 Local Development

App	Passed	Skipped
✅ astro-stable	82	6
✅ express-stable	82	6
✅ fastify-stable	82	6
✅ hono-stable	82	6
✅ nextjs-turbopack-canary	69	19
✅ nextjs-turbopack-stable	88	0
✅ nextjs-webpack-canary	69	19
✅ nextjs-webpack-stable	88	0
✅ nitro-stable	82	6
✅ nuxt-stable	82	6
✅ sveltekit-stable	82	6
✅ vite-stable	82	6

✅ 📦 Local Production

App	Passed	Skipped
✅ astro-stable	82	6
✅ express-stable	82	6
✅ fastify-stable	82	6
✅ hono-stable	82	6
✅ nextjs-turbopack-canary	69	19
✅ nextjs-turbopack-stable	88	0
✅ nextjs-webpack-canary	69	19
✅ nextjs-webpack-stable	88	0
✅ nitro-stable	82	6
✅ nuxt-stable	82	6
✅ sveltekit-stable	82	6
✅ vite-stable	82	6

✅ 🐘 Local Postgres

App	Passed	Skipped
✅ astro-stable	82	6
✅ express-stable	82	6
✅ fastify-stable	82	6
✅ hono-stable	82	6
✅ nextjs-turbopack-canary	69	19
✅ nextjs-turbopack-stable	88	0
✅ nextjs-webpack-canary	69	19
✅ nextjs-webpack-stable	88	0
✅ nitro-stable	82	6
✅ nuxt-stable	82	6
✅ sveltekit-stable	82	6
✅ vite-stable	82	6

✅ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack	88	0	0

❌ 🌍 Community Worlds

App	Passed	Failed
✅ mongodb-dev	5	0
❌ mongodb	58	11
✅ redis-dev	5	0
❌ redis	62	7
✅ turso-dev	5	0
❌ turso	4	65

✅ 📋 Other

App	Passed	Skipped
✅ e2e-local-dev-nest-stable	82	6
✅ e2e-local-postgres-nest-stable	82	6
✅ e2e-local-prod-nest-stable	82	6

📋 View full workflow run

❌ Some E2E test jobs failed:

Vercel Prod: failure
Local Dev: success
Local Prod: success
Local Postgres: success
Windows: success

Check the workflow run for details.

… 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>

VaguelySerious force-pushed the peter/stream-reconnect-proper branch from d76d170 to ee258dc Compare April 17, 2026 00:26

vercel bot deployed to Preview – workflow-web April 17, 2026 00:27 View deployment

vercel bot deployed to Preview – workflow-docs April 17, 2026 00:27 View deployment

vercel bot deployed to Preview – workbench-vite-workflow April 17, 2026 00:27 View deployment

vercel bot deployed to Preview – workbench-astro-workflow April 17, 2026 00:27 View deployment

vercel bot deployed to Preview – workbench-nitro-workflow April 17, 2026 00:27 View deployment

vercel bot deployed to Preview – workbench-express-workflow April 17, 2026 00:27 View deployment

vercel bot deployed to Preview – workbench-sveltekit-workflow April 17, 2026 00:27 View deployment

vercel bot deployed to Preview – workbench-hono-workflow April 17, 2026 00:28 View deployment

vercel bot deployed to Preview – workbench-nuxt-workflow April 17, 2026 00:28 View deployment

vercel bot deployed to Preview – workbench-fastify-workflow April 17, 2026 00:28 View deployment

vercel bot deployed to Preview – example-workflow April 17, 2026 00:28 View deployment

vercel bot deployed to Preview – example-nextjs-workflow-turbopack April 17, 2026 00:28 View deployment

vercel bot deployed to Preview – example-nextjs-workflow-webpack April 17, 2026 00:28 View deployment

vercel bot deployed to Preview – workflow-swc-playground April 17, 2026 00:30 View deployment

VaguelySerious changed the title ~~[world-vercel] Use stream control frame for transparent reconnection (proper streaming fix)~~ [world-vercel] Use stream control frame for transparent reconnection Apr 17, 2026

VaguelySerious marked this pull request as ready for review April 17, 2026 00:42

VaguelySerious requested a review from a team as a code owner April 17, 2026 00:42

TooTallNate approved these changes Apr 17, 2026

View reviewed changes

VaguelySerious merged commit 5ef9ac2 into stable Apr 17, 2026
87 of 89 checks passed

VaguelySerious deleted the peter/stream-reconnect-proper branch April 17, 2026 00:48

workflow-devkit-release-bot bot mentioned this pull request Apr 17, 2026

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[world-vercel] Use stream control frame for transparent reconnection#1790

[world-vercel] Use stream control frame for transparent reconnection#1790
VaguelySerious merged 1 commit intostablefrom
peter/stream-reconnect-proper

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VaguelySerious commented Apr 17, 2026

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