Drain released step stream writers before completion by alangenfeld · Pull Request #3941 · vercel/workflow

alangenfeld · 2026-09-02T21:12:36Z

Summary & Motivation

Situation

Workflow stream writers are expected to call releaseLock() when a step finishes writing so another step can acquire the stream.
The runtime observes that release and drains the server sink, but step_completed currently races the overall stream operation against 500ms.
A slow PUT can therefore continue under waitUntil while the next step starts and reads a stale tail.
Release can also happen while native writer.write() promises remain unsettled, leaving frames upstream of the server sink when a naive drain runs.
Writers intentionally kept locked must remain non-blocking so producer and consumer steps can overlap.

Fix

Treat a writer released before step return as an implicit durable handoff boundary.
At step end, acquire the unlocked stream with a temporary writer and enqueue an internal checkpoint behind all writes queued by the released writer.
Once the checkpoint crosses serialization, wait for those frames to reach the server sink and drain the group-commit PUT before step_completed.
If the writer remains locked, do not wait for durability; preserve the existing 500ms inline-loop heuristic and background waitUntil lifecycle.
Drain failures or the 30-second safety timeout fail/retry the step. Client disconnect errors remain non-fatal.

Test Plan

Covers released and held locks, release with unsettled writes, delayed first writer acquisition, forwarded writable arguments, drain timeout/failure, and multiple streams.
pnpm --filter @workflow/core build
pnpm --filter @workflow/core typecheck
pnpm --filter @workflow/core test — 2,405 passed, 3 expected failures, 1 skipped

Docs Preview

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Runtime tuning	Preview

changeset-bot · 2026-09-02T21:12:41Z

🦋 Changeset detected

Latest commit: ca0c499

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

This PR includes changesets to release 16 packages

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

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

vercel · 2026-09-02T21:12:43Z

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
example-nextjs-workflow-turbopack	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
example-nextjs-workflow-webpack	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
example-workflow	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
workbench-astro-workflow	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
workbench-express-workflow	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
workbench-fastify-workflow	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
workbench-hono-workflow	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
workbench-nestjs-workflow	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
workbench-nitro-workflow	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
workbench-nuxt-workflow	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
workbench-python-workflow	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
workbench-sveltekit-workflow	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
workbench-tanstack-start-workflow	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
workbench-vite-workflow	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
workflow-docs	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
workflow-swc-playground	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
workflow-tarballs	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC
workflow-web	Ready	Preview, v0	Sep 10, 2026 8:59pm UTC

github-actions · 2026-09-02T21:12:54Z

📊 Workflow Benchmarks

commit ca0c499 · Thu, 10 Sep 2026 21:19:47 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	196 (-81%) 💚	1274 🔴 (+9.6%)	1338 🔴 (+12%)	1725 🔴 (+31%) 🔻	30
TTFS	stream	187 (-23%) 💚	1357 🔴 (+23%) 🔻	1400 🔴 (+18%) 🔻	1422 🔴 (-5.8%)	30
TTFS	hook + stream	1456 (+19%) 🔻	1621 🔴 (+17%) 🔻	1673 🔴 (+9.0%)	1743 🔴 (-1.2%)	30
Fan-out TTFS	Promise.all(100 steps)	626 (-5.6%)	1905 (+110%) 🔻	1984 (+5.9%)	2260 (+15%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	1774 (+6.8%)	6523 (+13%)	8539 (+17%) 🔻	9246 (+14%)	10
STSO	1020 steps (inline)	116 (+3.6%)	158 (+3.9%)	197 (+12%)	357 (+19%) 🔻	1019
WO	1020 steps	156861 (+3.8%)	156861 (+3.8%)	156861 (+3.8%)	156861 (+3.8%)	1
CRTT	first chunk (pooled)	62 (±0%)	103 (-21%) 💚	137 (-21%) 💚	430 (-2.7%)	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	90.5 (-25%)	176 (-33%)	245 (-55%)	408 (-50%)	174 (-46%)	10
size sweep (100/s, 160B-12KB)	88.5 (-23%)	194 (-40%)	267 (-55%)	636 (-19%)	178 (-40%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	103 (+1%)	179 (-20%)	232 (-31%)	402 (-36%)	321 (-25%)	3
replay eve-gpt-5.6-sol-2000t (1x)	104 (±0%)	154 (-32%)	206 (-40%)	386 (-39%)	365 (-5%)	2
replay eve-gpt-5.6-sol-2000t (2x)	99 (-31%)	341 (+4%)	524 (+14%)	1042 (+18%)	492 (-22%)	3

📈 STSO distribution vs main (inline / queue-hop histograms)

1020 steps (inline)

Cumulative STSO time: main 150999ms → this run 156656ms (Δ +5657ms, +4%)

100-150 ms  █████████████████████┃██  main 743  this 681   -62
150-200 ms  ███████┃                  main 220  this 240   +20
200-250 ms  █┃                        main  43  this  60   +17
250-300 ms  ┃                         main   4  this  16   +12
300-350 ms  ┃                         main   3  this  11    +8
350-400 ms  ┃                         main   3  this   5    +2
400-450 ms  ┃                         main   2  this   1    -1
450-500 ms  ┃                         main   1  this   3    +2
500-550 ms  ┃                         main   0  this   2    +2

📈 CRTT drill-down vs main (RTT distributions & profiles)

variant  RTT 1ms→5s+             avg         p50         p90          p99     n
control  ······▂█▂····  145.5 (-31%)  134 (-23%)  245 (-55%)   408 (-50%)  3000
sweep    ······▂█▂▁···  159.4 (-33%)  146 (-27%)  267 (-55%)   636 (-19%)  3000
gw 1x    ·····▁▂█▂▁···  151.2 (-20%)  141 (-18%)  232 (-31%)   402 (-36%)  5295
eve 1x   ·····▁▄█▂▁···  132.8 (-32%)  115 (-29%)  206 (-40%)   386 (-39%)  5186
eve 2x   ·····▁▁█▇▂▁··   242.4 (-6%)   189 (-9%)  524 (+14%)  1042 (+18%)  7779

RTT over stream progress (avg per tenth of stream, bars scaled min→max):

control  ▇██▄▁▄▅▄▁▃  122–169ms
sweep    ▅▂▄█▃▃▁▁▄▃  132–212ms
gw 1x    ▆▄▁█▃▃▆▂▂▄  133–175ms
eve 1x   ▁▁█▄▂▇▃▃▂▂  119–161ms
eve 2x   ▂▁▂▃▁▂▃█▄▁  166–451ms

RTT by chunk size (avg per log size bin, ~160B → ~12KB serialized, bars scaled min→max):

sweep  ▁▆▆▂▁▇█  158–161ms

Delivery jitter over stream progress (avg positive CDV per tenth of stream, bars scaled min→max):

control  ▄█▆▆▃▆▅▄▁▄  40–53ms
sweep    ▁▂▇▅▅▆▅▅█▄  51–78ms
gw 1x    ▅▄▁▄▂▆█▂▃▅  38–56ms
eve 1x   ▂▁▆▅▂█▄▃▄▂  23–32ms
eve 2x   █▂▄▄▄▅▁▅▂▃  31–45ms

📜 Previous results (1)

`179ebf0`

Thu, 10 Sep 2026 20:32:20 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	291 (-71%) 💚	1334 🔴 (+19%) 🔻	1347 🔴 (+15%)	1464 🔴 (+22%) 🔻	30
TTFS	stream	290 (+41%) 🔻	1342 🔴 (+23%) 🔻	1363 🔴 (+21%) 🔻	1392 🔴 (+20%) 🔻	30
TTFS	hook + stream	1475 (+8.9%)	1614 🔴 (+8.0%)	1663 🔴 (+8.8%)	1748 🔴 (+6.7%)	30
Fan-out TTFS	Promise.all(100 steps)	602 (-11%)	881 (-21%) 💚	1992 (+4.5%)	2141 (+3.4%)	10
Fan-out TTLS	Promise.all(100 steps)	2020 (+16%) 🔻	5656 (+84%) 🔻	6205 (-30%) 💚	8270 (-9.4%)	10
STSO	1020 steps (inline)	108 (-21%) 💚	129 (-26%) 💚	146 (-26%) 💚	180 (-31%) 💚	1019
WO	1020 steps	130656 (-25%) 💚	130656 (-25%) 💚	130656 (-25%) 💚	130656 (-25%) 💚	1
CRTT	first chunk (pooled)	53 (-40%) 💚	85 (-38%) 💚	111 (-34%) 💚	319 (+64%) 🔻	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	67.5 (-37%)	123 (-54%)	163 (-68%)	311 (-71%)	113 (-53%)	10
size sweep (100/s, 160B-12KB)	72 (-42%)	131 (-72%)	225 (-87%)	605 (-88%)	163 (-44%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	64 (-53%)	129 (-66%)	204 (-60%)	547 (-44%)	364 (-37%)	3
replay eve-gpt-5.6-sol-2000t (1x)	195 (+56%)	127 (-42%)	180 (-47%)	437 (-22%)	372 (-12%)	2
replay eve-gpt-5.6-sol-2000t (2x)	81 (-40%)	172 (-53%)	239 (-61%)	601 (-49%)	365 (-38%)	3

ℹ️ Metric definitions & methodology

_{Streams: first-chunk RTT (the stream-open path, before any buffering/backpressure), CRTT percentiles, and worst delivery stall (CDV max). Cells are medians across iterations; per-run values in the artifacts. No 🔴/🟢 marks until targets attach.}

_{The collapsed STSO distribution section above buckets every step gap, split inline (same warm process — pure framework overhead) vs queue-hop (fresh process — dispatch, reinit, replay). █ = main, ┃ = this run, ░ = fill.}

_{The collapsed CRTT drill-down: per-variant RTT histograms (fixed log bins, · = empty) and mean RTT/positive-CDV profile lines over stream progress and chunk size. Histograms, avgs, and profiles merge exactly across runs; p50–p99 are percentile-of-percentiles. Per-index rows live in the artifacts.}

_{Best/P75/P90/P99 deltas compare against the most recent benchmark run on main at the time of this run. 🔻 flags a delta worse than +15%, 💚 one better than −15%.}

_{Metrics — TTFS: time to first step body (in-deployment start() → first step body) · Fan-out TTFS: fan-out time to first step (in-deployment start() → first of the parallel step bodies to complete) · Fan-out TTLS: fan-out time to last step (in-deployment start() → last of the parallel step bodies to complete, i.e. when the Promise.all resolves) · STSO: step-to-step overhead (gap between consecutive step bodies) · WO: workflow overhead (whole-run time outside step bodies, in-deployment anchored) · CRTT: chunk round-trip time (per-chunk write → read latency, one clock domain: deployment → stream backend → same deployment) · CDV: chunk delay variation / delivery jitter (inter-arrival gap minus inter-write gap per seq-adjacent pair; skew-free; the row is each run's MAX positive value, so one stall moves it)}

_{Scenarios — step: one trivial no-op step, no stream; no hooks, so the run stays in turbo mode (in-process fast path) · stream: one streaming step; no hooks, so the run stays in turbo mode (in-process fast path) · hook + stream: registers a hook before one step, which exits turbo mode (dispatch path) · 1020 steps: 1020 trivial sequential steps; STSO is measured between consecutive steps in the given step ranges, and WO is the whole-run overhead outside step bodies · Promise.all(100 steps): 100 trivial no-op steps started together in a single Promise.all; Fan-out TTFS is the first of them to complete and Fan-out TTLS the last, both from the in-deployment clientStart, so their gap is the spread the runtime adds across the fan-out · paced control (100/s, 60B): the control: 300 tiny (~60B) deltas metronome-paced at 100/s — zero workload structure, so it reads the transport floor and flush cadence, and disambiguates transport-wide vs workload-specific when a replay row moves · size sweep (100/s, 160B-12KB): same pacing as the control with deltas padded in rotation across seven log-spaced sizes (~160B–12KB) — rotation decouples size from stream position, so it isolates whether chunk size causes latency · replay gateway-gpt-5.4-nano-2000t (1x): raw provider SSE cadence captured at the AI gateway boundary (gpt-5.4-nano, the most popular gateway model; per-token deltas p50 208B = the modal production chunk size), replayed exactly as measured — the typical customer's workload; its CDV is the typical customer's real delivery jitter · replay eve-gpt-5.6-sol-2000t (1x): a captured eve turn (gpt-5.6-sol, the most-used demanding eve model; ~2000 output tokens = production p50 turn length) replayed exactly as measured — eve's envelope protocol re-ships the cumulative message so sizes ramp 142B→13KB; the demanding outlier tenant's reality · replay eve-gpt-5.6-sol-2000t (2x): the same eve capture at 2x — the headroom/stress row; real fast-tier models emit the same chunk sizes at proportionally higher rate, so time compression is a faithful speed model · first chunk (pooled): every run's seq-0 RTT pooled across all stream scenarios — the first chunk precedes any workload differentiation, so pooling samples one shared stream-open path with exact percentiles}

_{Replay cadences (semantic sha256) — eve-gpt-5.6-sol-2000t eaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t 6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 marks a percentile over its target (within target is left unmarked). Targets (p75/p90/p99, ms) — TTFS 200/300/600}

_{All timestamps are deployment-side; runs are triggered in-deployment, so the CI runner and api.vercel.com sit outside every measured window. TTFS = start() → first step body (includes dispatch + any cold start); Fan-out TTFS/TTLS = first/last step completion of one Promise.all from the same anchor (the gap is the runtime’s fan-out spread); STSO/WO between step bodies; CRTT inside the workflow (excludes the api.vercel.com read path).}

_{Cold starts stay in the numbers (real bursty-workload latency, inflates P75+); Best is the warm floor.}

github-actions · 2026-09-02T21:12:59Z

🧪 E2E Test Results

✅ All tests passed

⚠️ Flaky E2E Tests (passed on retry)

These tests failed at least once and passed on a retry. A recurring entry here is a real race worth investigating.

cancelRun via CLI - cancelling a running workflow (express)
cancelRun via CLI - cancelling a running workflow (nextjs-turbopack)
cancelRun via CLI - cancelling a running workflow (nextjs-webpack)
hookDisposeTestWorkflow - hook token reuse after explicit disposal while workflow still running (sveltekit)
hookWithSleepWorkflow - hook payloads delivered correctly with concurrent sleep (nextjs-webpack)

🛠 Infra Events (absorbed by the harness)

Platform anomalies the e2e harness detected and worked around (e.g. a run the queue never picked up, replaced by a fresh run). Clustered timestamps indicate a backend blip; a steady drip indicates a platform issue worth escalating.

cold-start-warmup · suite warmup (tanstack-start) · at 21:00:27Z · abandoned wrun_01M26HXHSK5DKHTE1C1BQSKTP7
cold-start-warmup · suite warmup (astro) · at 21:00:51Z · abandoned wrun_01M26HYM8PB7TSY12JDXC1CW0F
run-pickup-stall · plainModuleDoneHook resumed via plain API route (o2flow shape) (nextjs-webpack) · at 21:08:34Z · abandoned wrun_01M26JCT7SXRXW06F5XTYJ26BW
run-pickup-stall · hookWithSleepWorkflow - hook payloads delivered correctly with concurrent sleep (nextjs-webpack) · at 21:08:36Z · abandoned wrun_01M26JCVN34TSYACPBXY10VCB0

E2E Test Summary

Summary

	Passed	Skipped	Total
✅ ▲ Vercel Production	3662	685	4347
✅ 💻 Local Development	3922	586	4508
✅ 📦 Local Production	3922	586	4508
✅ 🐘 Local Postgres	3922	586	4508
✅ 🪟 Windows	320	2	322
✅ 🌐 Cross-language Conformance	68	74	142
✅ vercel-http-transport	823	143	966
✅ vercel-multi-region	27	0	27
✅ vercel-ws-transport	557	87	644
Total	17223	2749	19972

Details by Category

✅ ▲ Vercel Production

App	Passed	Skipped
✅ astro-node	133	28
✅ astro-quickjs	133	28
✅ example-node	133	28
✅ example-quickjs	133	28
✅ express-node	133	28
✅ express-quickjs	133	28
✅ fastify-node	133	28
✅ fastify-quickjs	133	28
✅ hono-node	133	28
✅ hono-quickjs	133	28
✅ nest-node	133	28
✅ nest-quickjs	133	28
✅ nextjs-turbopack-node	158	3
✅ nextjs-turbopack-quickjs	158	3
✅ nextjs-webpack-node	158	3
✅ nextjs-webpack-quickjs	158	3
✅ nitro-node	133	28
✅ nitro-quickjs	133	28
✅ nuxt-node	133	28
✅ nuxt-quickjs	133	28
✅ python-node	66	95
✅ sveltekit-node	152	9
✅ sveltekit-quickjs	152	9
✅ tanstack-start-node	133	28
✅ tanstack-start-quickjs	133	28
✅ vite-node	133	28
✅ vite-quickjs	133	28

✅ 💻 Local Development

App	Passed	Skipped
✅ astro-stable-node	134	27
✅ astro-stable-quickjs	134	27
✅ express-stable-node	134	27
✅ express-stable-quickjs	134	27
✅ fastify-stable-node	134	27
✅ fastify-stable-quickjs	134	27
✅ hono-stable-node	134	27
✅ hono-stable-quickjs	134	27
✅ nest-stable-node	134	27
✅ nest-stable-quickjs	134	27
✅ nextjs-turbopack-canary-node	141	20
✅ nextjs-turbopack-canary-quickjs	141	20
✅ nextjs-turbopack-stable-node	160	1
✅ nextjs-turbopack-stable-quickjs	160	1
✅ nextjs-webpack-canary-node	141	20
✅ nextjs-webpack-canary-quickjs	141	20
✅ nextjs-webpack-stable-node	160	1
✅ nextjs-webpack-stable-quickjs	160	1
✅ nitro-stable-node	134	27
✅ nitro-stable-quickjs	134	27
✅ nuxt-stable-node	134	27
✅ nuxt-stable-quickjs	134	27
✅ sveltekit-stable-node	153	8
✅ sveltekit-stable-quickjs	153	8
✅ tanstack-start-node	134	27
✅ tanstack-start-quickjs	134	27
✅ vite-stable-node	134	27
✅ vite-stable-quickjs	134	27

✅ 📦 Local Production

App	Passed	Skipped
✅ astro-stable-node	134	27
✅ astro-stable-quickjs	134	27
✅ express-stable-node	134	27
✅ express-stable-quickjs	134	27
✅ fastify-stable-node	134	27
✅ fastify-stable-quickjs	134	27
✅ hono-stable-node	134	27
✅ hono-stable-quickjs	134	27
✅ nest-stable-node	134	27
✅ nest-stable-quickjs	134	27
✅ nextjs-turbopack-canary-node	141	20
✅ nextjs-turbopack-canary-quickjs	141	20
✅ nextjs-turbopack-stable-node	160	1
✅ nextjs-turbopack-stable-quickjs	160	1
✅ nextjs-webpack-canary-node	141	20
✅ nextjs-webpack-canary-quickjs	141	20
✅ nextjs-webpack-stable-node	160	1
✅ nextjs-webpack-stable-quickjs	160	1
✅ nitro-stable-node	134	27
✅ nitro-stable-quickjs	134	27
✅ nuxt-stable-node	134	27
✅ nuxt-stable-quickjs	134	27
✅ sveltekit-stable-node	153	8
✅ sveltekit-stable-quickjs	153	8
✅ tanstack-start-node	134	27
✅ tanstack-start-quickjs	134	27
✅ vite-stable-node	134	27
✅ vite-stable-quickjs	134	27

✅ 🐘 Local Postgres

App	Passed	Skipped
✅ astro-stable-node	134	27
✅ astro-stable-quickjs	134	27
✅ express-stable-node	134	27
✅ express-stable-quickjs	134	27
✅ fastify-stable-node	134	27
✅ fastify-stable-quickjs	134	27
✅ hono-stable-node	134	27
✅ hono-stable-quickjs	134	27
✅ nest-stable-node	134	27
✅ nest-stable-quickjs	134	27
✅ nextjs-turbopack-canary-node	141	20
✅ nextjs-turbopack-canary-quickjs	141	20
✅ nextjs-turbopack-stable-node	160	1
✅ nextjs-turbopack-stable-quickjs	160	1
✅ nextjs-webpack-canary-node	141	20
✅ nextjs-webpack-canary-quickjs	141	20
✅ nextjs-webpack-stable-node	160	1
✅ nextjs-webpack-stable-quickjs	160	1
✅ nitro-stable-node	134	27
✅ nitro-stable-quickjs	134	27
✅ nuxt-stable-node	134	27
✅ nuxt-stable-quickjs	134	27
✅ sveltekit-stable-node	153	8
✅ sveltekit-stable-quickjs	153	8
✅ tanstack-start-node	134	27
✅ tanstack-start-quickjs	134	27
✅ vite-stable-node	134	27
✅ vite-stable-quickjs	134	27

✅ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack-node	160	0	1
✅ nextjs-turbopack-quickjs	160	0	1

✅ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
✅ python	68	0	74

✅ vercel-http-transport

App	Passed	Skipped
✅ example	133	28
✅ express	133	28
✅ hono	133	28
✅ nextjs-turbopack	158	3
✅ nitro	133	28
✅ vite	133	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Skipped
✅ example	133	28
✅ express	133	28
✅ nextjs-turbopack	158	3
✅ vite	133	28

📋 View full workflow run

github-actions · 2026-09-02T21:16:37Z

Sim World

Simulated world deterministic testing for races. Traces

🟠 world-sim scenario book — 1 fail of 41 total

fence=per-spec

scenario	outcome	events	virt	replay
✅ `smoke-no-steps`	completed	3	0ms	ok
✅ `smoke-one-step`	completed	6	0ms	ok
✅ `hook-at-step-started`	completed	12	0ms	ok
✅ `hook-at-step-completed`	completed	12	0ms	ok
✅ `hook-at-hook-created`	completed	12	0ms	ok
✅ `deadline-hook-wins`	completed	7	1.0h	ok
✅ `deadline-expires`	completed	7	1.0h	ok
✅ `long-sleep`	completed	11	30.0d	ok
✅ `hook-never-arrives`	stalled	3	0ms	skipped
✅ `step-retries-twice`	completed	10	2.0s	ok
✅ `parallel-steps`	completed	9	0ms	ok
✅ `hook-on-execution-state`	completed	12	0ms	ok
✅ `peek-hook-before-branch`	completed	12	0ms	ok
✅ `peek-hook-after-branch`	completed	12	0ms	ok
✅ `peek-hook-at-registration`	completed	12	0ms	ok
✅ `race-hook-before-probe`	completed	12	0ms	ok
✅ `race-hook-after-probe`	completed	12	0ms	ok
✅ `race-duplicate-delivery`	completed	13	0ms	ok
✅ `attr-hook-before-step`	completed	11	0ms	ok
✅ `attr-hook-after-step`	completed	11	0ms	ok
✅ `attr-from-step-body`	completed	13	0ms	ok
✅ `fork-hook-after-timeout`	completed	14	1.0m	ok
✅ `fork-hook-before-timeout`	completed	14	1.0m	ok
✅ `count-hook-after-timeout`	completed	17	1.0m	ok
✅ `count-hook-before-timeout`	completed	20	1.0m	ok
✅ `stale-read-step-count-fork`	completed	20	1.0m	ok
✅ `stale-read-equal-step-counts`	completed	14	1.0m	ok
✅ `step-vs-step-fork`	completed	12	0ms	ok
✅ `step-vs-step-fork-fenced`	completed	12	0ms	ok
✅ `fence-catches-benign-direction`	completed	12	5ms	ok
✅ `in-flight-before-decision`	completed	17	1.0m	ok
❌ `in-flight-before-decision-counted`	completed	17	1.0m	ok
✅ `in-flight-after-decision`	completed	19	2.0m	ok
✅ `stale-read-step-count-fork-fenced`	completed	20	1.0m	ok
✅ `fork-hook-wins`	completed	13	1.0m	ok
✅ `fork-timeout-wins`	completed	13	1.0m	ok
✅ `unclaimed-payload-under-fork`	completed	17	1.0m	ok
✅ `claimed-payload-under-fork`	completed	17	1.0m	ok
✅ `writers-independent-step-bodies`	completed	12	0ms	ok
✅ `writers-scripted-tempo`	completed	12	0ms	ok
✅ `cancel-mid-step`	cancelled	7	0ms	skipped

Full trace: world-sim.txt

github-actions · 2026-09-02T21:17:20Z

Framework	Flow route	Step reg.	Framework output
hono	201.6 KiB (±0)	42.3 KiB (±0)	1.79 MiB (+1.1 KiB)
nextjs-turbopack	207.8 KiB (±0)	439 B (±0)	776.4 KiB (+570 B)

About these numbers

Sizes are gzip; parentheses show the change against main.
Flow route and Step reg. gate this job, on raw bytes rather than the gzip shown, at max(2%, 50.0 KiB). Framework output is informational.

ca0c499 · run

TooTallNate

AI: Requesting changes because explicitly closing a workflow writable currently turns a successful streaming step into retries/failure. The focused unit tests pass, but they do not cover this terminal-stream path; the failing benchmark run confirms the regression.

TooTallNate

AI: Approved on re-review at ca0c499. Both remaining blockers are fixed: downstream errors now propagate to idle pipeTo() producers, and snapshot failures preserve accepted-prefix durability before rejecting. The original normal-close fix remains intact. No new blocking findings in the latest delta or targeted close/abort/lock lifecycle checks. Validation: 269 focused tests passed across flushable-stream, step-executor, serialization, and step/writable-stream; both original actual-serializer reproductions also pass with the corrected invariants. Tests used PR-head workspace sources and installed third-party dependencies whose lockfile matches this head. Some CI jobs are still running; this approval does not claim a completed CI run. No deployed E2E or benchmark was rerun locally.

github-actions · 2026-09-11T14:22:48Z

No backport to stable for c09c1bb (AI decision).

This is a genuine correctness fix (released stream writers' frames must reach durable storage before step_completed), but it is built entirely on main-only infrastructure: packages/core/src/runtime/step-executor.ts does not exist on stable (v4.8.8 uses step-handler.ts, which flushes stream ops purely in the background via waitUntil with no inline race), and stable's flushable-stream.ts has none of the group-commit drain-barrier machinery (drainBarrier/STREAM_DRAIN_SYMBOL) whose early-ack behavior this patch is correcting. It also adds a new env var (WORKFLOW_STEP_STREAM_DRAIN_TIMEOUT_MS) documented only under docs/content/docs/v5/. Porting it would mean reimplementing the barrier against a different v4 stream lifecycle rather than cherry-picking a fix; force it via workflow_dispatch only if the same data-staleness bug is confirmed on the v4 stream path.

To override, re-run the Backport to stable workflow manually via workflow_dispatch and paste this commit SHA into the ref input:

c09c1bb6ea743d6c8e24574aa8dd5516fb287548

main advanced since the previous merge (notably #3902's Zod 4.5 upgrade and #3941's step-stream drain fix). Only pnpm-lock.yaml conflicted; resolved by taking main's lockfile and reinstalling to fold this branch's ai-sdk-v7 named catalog additions back in. Everything else merged cleanly. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Upstream vercel/workflow#3941 ships the same fix in 5.0.0-beta.51. Record it and the pending createHook force-claim API as merge prerequisites in the research doc instead of carrying a vendored runtime patch. Signed-off-by: Andrew Barba <barba@hey.com>

main now vendors beta.51, which includes vercel/workflow#3941. The integration test gated on that release runs unconditionally, and the research doc records the remaining Workflow prerequisite as the force-claim hook API. Signed-off-by: Andrew Barba <barba@hey.com>

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alangenfeld force-pushed the alangenfeld/workflow-released-writer-drain branch from 856a910 to fc449bc Compare September 3, 2026 14:58

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TooTallNate approved these changes Sep 10, 2026

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alangenfeld merged commit c09c1bb into main Sep 11, 2026
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alangenfeld deleted the alangenfeld/workflow-released-writer-drain branch September 11, 2026 14:21

github-actions Bot mentioned this pull request Sep 11, 2026

Version Packages (beta) #4071

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github-actions Bot mentioned this pull request Sep 11, 2026

Version Packages ben-vargas/workflow#104

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github-actions Bot mentioned this pull request Sep 11, 2026

Version Packages (beta) Jokacar10/jkworkflow#548

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AndrewBarba mentioned this pull request Sep 12, 2026

feat(eve): run sessions in one owner workflow with deployment handoff vercel/eve#3263

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alangenfeld mentioned this pull request Sep 24, 2026

fix(core): refresh pending ops after stream durability waits #4387

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Drain released step stream writers before completion - #3941

Drain released step stream writers before completion#3941
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