[core] Retain workflow VMs across attributes

[NathanColosimo]

Summary

• retain the workflow VM across workflow attribute writes
• generation-guard attribute suspension signals
• keep waits on the cold-replay path

Verification

• pnpm --filter @workflow/core... build
• pnpm --filter @workflow/core test
• pnpm --filter @workflow/core typecheck
• focused Biome check (existing complexity warnings only)

[changeset-bot]

🦋 Changeset detected

Latest commit: f980c84

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]

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

Project	Deployment	Actions	Updated (UTC)
example-nextjs-workflow-turbopack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-nextjs-workflow-webpack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-astro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-express-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-fastify-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-hono-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nestjs-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nitro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nuxt-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-python-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-sveltekit-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-tanstack-start-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-vite-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-swc-playground	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-tarballs	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-web	Ready	Preview, v0	Aug 25, 2026 10:13pm

1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
workflow-docs	Skipped	v0	Aug 25, 2026 10:13pm

[github-actions]

🧪 E2E Test Results

❌ Some tests failed

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

python-node (8 failed):

• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP | 🔍 observability
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG | 🔍 observability
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8 | 🔍 observability
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR | 🔍 observability
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8 | 🔍 observability
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ | 🔍 observability
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R | 🔍 observability
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W | 🔍 observability

🌐 Cross-language Conformance (9 failed)

python (9 failed):

• deploymentId: 'latest' is a no-op in non-Vercel worlds | wrun_01M0XFVJ4Q5N1HH8PZ8PNMZJGM
• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W

⚠️ 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.

• addTenWorkflow (nitro)
• deploymentId: 'latest' is a no-op in non-Vercel worlds (nest)
• promiseAllWorkflow (tanstack-start)

🛠 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.

36 infra events

• cold-start-warmup · suite warmup (tanstack-start) · at 22:12:44Z · abandoned wrun_01M0XFPDAXWJQ7SD4FCKWQZYRA
• run-pickup-stall · readableStreamWorkflow (nuxt) · at 22:13:10Z · abandoned wrun_01M0XFQJSYN1EQ26EFWPB3FX7R
• cold-start-warmup · suite warmup (python) · at 22:13:14Z · abandoned wrun_41M0XFMGBW0GW4N24MJB4H7RZ2 · (+7 more)
• run-pickup-stall · promiseAllWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5680GKBWE9XG0BBRZ9M
• run-pickup-stall · nullByteWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56G0GGHTT01RVT5ZPQR
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56D0GGXH8CCPSM3Z9K0
• run-pickup-stall · sleepingWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56C0GNDC6T0ZY9S0GWJ
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5FK0GT4GR0302EQNF4C
• cold-start-warmup · suite warmup (python) · at 22:13:50Z · abandoned wrun_01M0XFNKQ582S72PXQHAGBHJWF · (+7 more)
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:14:03Z · abandoned wrun_41M0XFS5AQ0GQYVWX4P4E6BHBP
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VG6MYP4JCRF0YND76P
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VHYJRWT478MJQ5ATEM
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VPDWD6VRV31BCMBYKY
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VR3R0PYV37K2YVRRRT
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VS4X2AZC5TRBB4JGXA
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0FH0GMQFFRGHVXJJ4Z8
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0HP0GSMD2Y4Y5A9Z9YN
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KQ0GSSSERV48EGPZSX
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KW0GG34XF8JV5G9XBZ
• run-pickup-stall · spawnWorkflowFromStepWorkflow - spawning a child workflow using start() inside a step (nuxt) · at 22:14:36Z · abandoned wrun_01M0XFT6K1JSH0VSC613AMTMGZ
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FJRBBQF23Q3566PCDC
• run-pickup-stall · nullByteWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FKN4FY46S8NDW7FZC3
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FD12ZSSQN6DBYV3TYQ
• run-pickup-stall · sleepingWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FHR4YF1YXKYJEBBFF8
• run-pickup-stall · promiseAllWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FFR71T5MAHWFM1Q4XZ
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:15:21Z · abandoned wrun_41M0XFT4Y30GMP0Z8BB64YMFJV
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY33ZDAP24JG416SA097
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3AQJN5VYNF0Q0J4EWH
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3EYEP30QARW9VV86X7
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEHZ4Q2CVSNNP7Z9KYH
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEJ4WZR29NMCBTBKBQ3
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 22:16:56Z · abandoned wrun_01M0XFYFBN0RT2K0DG7ZMKDBMN
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 22:17:00Z · abandoned wrun_01M0XFYK9380895PK345J1CJ1D
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:17:02Z · abandoned wrun_41M0XFWWTM0GJJ8E84Y8DP0DJN
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:03Z · abandoned wrun_41M0XFWRC40GSMR0C35G2N42CZ
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:05Z · abandoned wrun_01M0XFYRPJNQB6GCV3QJYQ45M9

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
❌ ▲ Vercel Production	3570	8	742	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
❌ 🌐 Cross-language Conformance	0	9	132	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17053	17	2778	19848

Details by Category

❌ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
❌ python-node	0	8	152
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

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

❌ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
❌ python	0	9	132

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

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

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit f980c84 · Tue, 25 Aug 2026 22:35:16 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1289 (+30%) 🔻	1390 🔴 (+27%) 🔻	1423 🔴 (+26%) 🔻	1502 🔴 (+14%)	30
TTFS	stream	251 (-15%) 💚	1370 🔴 (+21%) 🔻	1390 🔴 (+21%) 🔻	1511 🔴 (+24%) 🔻	30
TTFS	hook + stream	1587 (+20%) 🔻	1724 🔴 (+19%) 🔻	1776 🔴 (+18%) 🔻	5891 🔴 (+283%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	652 (+5.8%)	2053 (+65%) 🔻	2209 (+18%) 🔻	2396 (+21%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	2103 (-2.0%)	4041 (+3.2%)	4273 (-33%) 💚	11906 (+45%) 🔻	10
STSO	1020 steps (inline)	121 (+17%) 🔻	161 (-12%)	178 (-15%)	236 (-72%) 💚	1019
WO	1020 steps	159955 (-15%)	159955 (-15%)	159955 (-15%)	159955 (-15%)	1
CRTT	first chunk (pooled)	119 (-2.5%)	183 (+11%)	212 (+9.8%)	329 (-18%) 💚	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	147 (+2%)	170 (-23%)	208 (-56%)	320 (-61%)	120 (-47%)	10
size sweep (100/s, 160B-12KB)	134 (-6%)	196 (-5%)	310 (+12%)	536 (+25%)	138 (-21%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	149 (-6%)	157 (-20%)	188 (-28%)	409 (-13%)	263 (-13%)	3
replay eve-gpt-5.6-sol-2000t (1x)	167 (+4%)	144 (-19%)	180 (-19%)	360 (-5%)	214 (-28%)	2
replay eve-gpt-5.6-sol-2000t (2x)	139 (-5%)	191 (-64%)	250 (-75%)	404 (-75%)	241 (-76%)	3

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

1020 steps (inline)

Cumulative STSO time: main 186880ms → this run 159772ms (Δ -27108ms, -15%)

100-150 ms █░░░░░░░░░░┃ main 40 this 434 +394
150-200 ms ███████████████┃████████ main 841 this 557 -284
200-250 ms ┃██ main 104 this 21 -83
250-300 ms ┃ main 17 this 3 -14
300-350 ms ┃ main 0 this 4 +4
350-400 ms ┃ main 2 this 0 -2
400-450 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
800-850 ms ┃ main 2 this 0 -2
850-900 ms ┃ main 10 this 0 -10
900-950 ms ┃ main 1 this 0 -1

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

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▂█▁···· 142.1 (-17%) 136 (-5%) 208 (-56%) 320 (-61%) 3000
sweep ······▂█▂▁··· 149.8 (-10%) 133 (-14%) 310 (+12%) 536 (+25%) 3000
gw 1x ·····▁▃█▁▁··· 131.6 (-16%) 125 (-12%) 188 (-28%) 409 (-13%) 5295
eve 1x ·····▁▃█▁···· 126.6 (-17%) 117 (-15%) 180 (-19%) 360 (-5%) 5186
eve 2x ·····▁▁█▃···· 163.7 (-50%) 151 (-27%) 250 (-75%) 404 (-75%) 7779

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

control █▅▄▄▃▃▄▃▁▄ 126–162ms
sweep █▃▅▆▂▃█▇▄▁ 130–168ms
gw 1x ▃▃▆▅▂▄█▅█▁ 121–143ms
eve 1x ▄▂▄▄▂▂▆█▃▁ 115–151ms
eve 2x ▅▂▄▃▁▅▇█▆▄ 132–196ms

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

sweep ▅█▆▄▁▁▁ 148–153ms

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

control ▁▅▄▇▇▄█▃▂▃ 38–47ms
sweep ▁▂▆▇▃▆█▅▆▃ 43–67ms
gw 1x ▂▃▃▁▃▄█▅▄▂ 35–48ms
eve 1x ▅▄▃▅▄▇██▄▁ 21–25ms
eve 2x █▆▅▄▄▇▄▁▄▅ 21–29ms

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-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 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.}

[VaguelySerious]

AI review: blocking issues found

[VaguelySerious]

LGTM assuming e2e passes (except python)

[TooTallNate]

AI: Approved. I found no blocking issues in the attribute-retention changes relative to the stacked #3604 base.

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.5 KiB (±0)	1.76 MiB (-106 B)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	763.2 KiB (+353 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.

f980c84 · run

[github-actions]

No backport to stable for 82e2678 (AI decision).

This commit extends the retained-VM optimization to cover workflow attribute writes, making attribute suspensions retainable (new generation guard for attribute signals, no_step_driver becomes no_replay_driver). It is a performance enhancement to an existing optimization path, not a fix for a correctness, crash, or data-loss defect on stable, and it changes when a live VM is resumed versus cold-replayed — behavior risk a maintenance line should not take on. The patch changeset does not make it a stability fix.

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

82e267893917e06f5d3ce316baefc27cd024a912

[NathanColosimo]

Summary

• retain the workflow VM across workflow attribute writes
• generation-guard attribute suspension signals
• keep waits on the cold-replay path

Verification

• pnpm --filter @workflow/core... build
• pnpm --filter @workflow/core test
• pnpm --filter @workflow/core typecheck
• focused Biome check (existing complexity warnings only)

[changeset-bot]

🦋 Changeset detected

Latest commit: f980c84

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]

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

Project	Deployment	Actions	Updated (UTC)
example-nextjs-workflow-turbopack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-nextjs-workflow-webpack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-astro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-express-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-fastify-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-hono-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nestjs-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nitro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nuxt-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-python-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-sveltekit-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-tanstack-start-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-vite-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-swc-playground	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-tarballs	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-web	Ready	Preview, v0	Aug 25, 2026 10:13pm

1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
workflow-docs	Skipped	v0	Aug 25, 2026 10:13pm

[github-actions]

🧪 E2E Test Results

❌ Some tests failed

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

python-node (8 failed):

• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP | 🔍 observability
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG | 🔍 observability
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8 | 🔍 observability
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR | 🔍 observability
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8 | 🔍 observability
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ | 🔍 observability
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R | 🔍 observability
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W | 🔍 observability

🌐 Cross-language Conformance (9 failed)

python (9 failed):

• deploymentId: 'latest' is a no-op in non-Vercel worlds | wrun_01M0XFVJ4Q5N1HH8PZ8PNMZJGM
• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W

⚠️ 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.

• addTenWorkflow (nitro)
• deploymentId: 'latest' is a no-op in non-Vercel worlds (nest)
• promiseAllWorkflow (tanstack-start)

🛠 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.

36 infra events

• cold-start-warmup · suite warmup (tanstack-start) · at 22:12:44Z · abandoned wrun_01M0XFPDAXWJQ7SD4FCKWQZYRA
• run-pickup-stall · readableStreamWorkflow (nuxt) · at 22:13:10Z · abandoned wrun_01M0XFQJSYN1EQ26EFWPB3FX7R
• cold-start-warmup · suite warmup (python) · at 22:13:14Z · abandoned wrun_41M0XFMGBW0GW4N24MJB4H7RZ2 · (+7 more)
• run-pickup-stall · promiseAllWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5680GKBWE9XG0BBRZ9M
• run-pickup-stall · nullByteWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56G0GGHTT01RVT5ZPQR
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56D0GGXH8CCPSM3Z9K0
• run-pickup-stall · sleepingWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56C0GNDC6T0ZY9S0GWJ
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5FK0GT4GR0302EQNF4C
• cold-start-warmup · suite warmup (python) · at 22:13:50Z · abandoned wrun_01M0XFNKQ582S72PXQHAGBHJWF · (+7 more)
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:14:03Z · abandoned wrun_41M0XFS5AQ0GQYVWX4P4E6BHBP
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VG6MYP4JCRF0YND76P
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VHYJRWT478MJQ5ATEM
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VPDWD6VRV31BCMBYKY
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VR3R0PYV37K2YVRRRT
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VS4X2AZC5TRBB4JGXA
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0FH0GMQFFRGHVXJJ4Z8
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0HP0GSMD2Y4Y5A9Z9YN
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KQ0GSSSERV48EGPZSX
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KW0GG34XF8JV5G9XBZ
• run-pickup-stall · spawnWorkflowFromStepWorkflow - spawning a child workflow using start() inside a step (nuxt) · at 22:14:36Z · abandoned wrun_01M0XFT6K1JSH0VSC613AMTMGZ
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FJRBBQF23Q3566PCDC
• run-pickup-stall · nullByteWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FKN4FY46S8NDW7FZC3
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FD12ZSSQN6DBYV3TYQ
• run-pickup-stall · sleepingWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FHR4YF1YXKYJEBBFF8
• run-pickup-stall · promiseAllWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FFR71T5MAHWFM1Q4XZ
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:15:21Z · abandoned wrun_41M0XFT4Y30GMP0Z8BB64YMFJV
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY33ZDAP24JG416SA097
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3AQJN5VYNF0Q0J4EWH
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3EYEP30QARW9VV86X7
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEHZ4Q2CVSNNP7Z9KYH
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEJ4WZR29NMCBTBKBQ3
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 22:16:56Z · abandoned wrun_01M0XFYFBN0RT2K0DG7ZMKDBMN
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 22:17:00Z · abandoned wrun_01M0XFYK9380895PK345J1CJ1D
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:17:02Z · abandoned wrun_41M0XFWWTM0GJJ8E84Y8DP0DJN
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:03Z · abandoned wrun_41M0XFWRC40GSMR0C35G2N42CZ
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:05Z · abandoned wrun_01M0XFYRPJNQB6GCV3QJYQ45M9

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
❌ ▲ Vercel Production	3570	8	742	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
❌ 🌐 Cross-language Conformance	0	9	132	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17053	17	2778	19848

Details by Category

❌ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
❌ python-node	0	8	152
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

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

❌ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
❌ python	0	9	132

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

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

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit f980c84 · Tue, 25 Aug 2026 22:35:16 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1289 (+30%) 🔻	1390 🔴 (+27%) 🔻	1423 🔴 (+26%) 🔻	1502 🔴 (+14%)	30
TTFS	stream	251 (-15%) 💚	1370 🔴 (+21%) 🔻	1390 🔴 (+21%) 🔻	1511 🔴 (+24%) 🔻	30
TTFS	hook + stream	1587 (+20%) 🔻	1724 🔴 (+19%) 🔻	1776 🔴 (+18%) 🔻	5891 🔴 (+283%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	652 (+5.8%)	2053 (+65%) 🔻	2209 (+18%) 🔻	2396 (+21%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	2103 (-2.0%)	4041 (+3.2%)	4273 (-33%) 💚	11906 (+45%) 🔻	10
STSO	1020 steps (inline)	121 (+17%) 🔻	161 (-12%)	178 (-15%)	236 (-72%) 💚	1019
WO	1020 steps	159955 (-15%)	159955 (-15%)	159955 (-15%)	159955 (-15%)	1
CRTT	first chunk (pooled)	119 (-2.5%)	183 (+11%)	212 (+9.8%)	329 (-18%) 💚	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	147 (+2%)	170 (-23%)	208 (-56%)	320 (-61%)	120 (-47%)	10
size sweep (100/s, 160B-12KB)	134 (-6%)	196 (-5%)	310 (+12%)	536 (+25%)	138 (-21%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	149 (-6%)	157 (-20%)	188 (-28%)	409 (-13%)	263 (-13%)	3
replay eve-gpt-5.6-sol-2000t (1x)	167 (+4%)	144 (-19%)	180 (-19%)	360 (-5%)	214 (-28%)	2
replay eve-gpt-5.6-sol-2000t (2x)	139 (-5%)	191 (-64%)	250 (-75%)	404 (-75%)	241 (-76%)	3

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

1020 steps (inline)

Cumulative STSO time: main 186880ms → this run 159772ms (Δ -27108ms, -15%)

100-150 ms █░░░░░░░░░░┃ main 40 this 434 +394
150-200 ms ███████████████┃████████ main 841 this 557 -284
200-250 ms ┃██ main 104 this 21 -83
250-300 ms ┃ main 17 this 3 -14
300-350 ms ┃ main 0 this 4 +4
350-400 ms ┃ main 2 this 0 -2
400-450 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
800-850 ms ┃ main 2 this 0 -2
850-900 ms ┃ main 10 this 0 -10
900-950 ms ┃ main 1 this 0 -1

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

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▂█▁···· 142.1 (-17%) 136 (-5%) 208 (-56%) 320 (-61%) 3000
sweep ······▂█▂▁··· 149.8 (-10%) 133 (-14%) 310 (+12%) 536 (+25%) 3000
gw 1x ·····▁▃█▁▁··· 131.6 (-16%) 125 (-12%) 188 (-28%) 409 (-13%) 5295
eve 1x ·····▁▃█▁···· 126.6 (-17%) 117 (-15%) 180 (-19%) 360 (-5%) 5186
eve 2x ·····▁▁█▃···· 163.7 (-50%) 151 (-27%) 250 (-75%) 404 (-75%) 7779

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

control █▅▄▄▃▃▄▃▁▄ 126–162ms
sweep █▃▅▆▂▃█▇▄▁ 130–168ms
gw 1x ▃▃▆▅▂▄█▅█▁ 121–143ms
eve 1x ▄▂▄▄▂▂▆█▃▁ 115–151ms
eve 2x ▅▂▄▃▁▅▇█▆▄ 132–196ms

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

sweep ▅█▆▄▁▁▁ 148–153ms

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

control ▁▅▄▇▇▄█▃▂▃ 38–47ms
sweep ▁▂▆▇▃▆█▅▆▃ 43–67ms
gw 1x ▂▃▃▁▃▄█▅▄▂ 35–48ms
eve 1x ▅▄▃▅▄▇██▄▁ 21–25ms
eve 2x █▆▅▄▄▇▄▁▄▅ 21–29ms

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-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 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.}

[VaguelySerious]

AI review: blocking issues found

[VaguelySerious]

LGTM assuming e2e passes (except python)

[TooTallNate]

AI: Approved. I found no blocking issues in the attribute-retention changes relative to the stacked #3604 base.

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.5 KiB (±0)	1.76 MiB (-106 B)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	763.2 KiB (+353 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.

f980c84 · run

[github-actions]

No backport to stable for 82e2678 (AI decision).

This commit extends the retained-VM optimization to cover workflow attribute writes, making attribute suspensions retainable (new generation guard for attribute signals, no_step_driver becomes no_replay_driver). It is a performance enhancement to an existing optimization path, not a fix for a correctness, crash, or data-loss defect on stable, and it changes when a live VM is resumed versus cold-replayed — behavior risk a maintenance line should not take on. The patch changeset does not make it a stability fix.

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

82e267893917e06f5d3ce316baefc27cd024a912

[NathanColosimo]

Summary

• retain the workflow VM across workflow attribute writes
• generation-guard attribute suspension signals
• keep waits on the cold-replay path

Verification

• pnpm --filter @workflow/core... build
• pnpm --filter @workflow/core test
• pnpm --filter @workflow/core typecheck
• focused Biome check (existing complexity warnings only)

[changeset-bot]

🦋 Changeset detected

Latest commit: f980c84

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]

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

Project	Deployment	Actions	Updated (UTC)
example-nextjs-workflow-turbopack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-nextjs-workflow-webpack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-astro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-express-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-fastify-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-hono-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nestjs-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nitro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nuxt-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-python-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-sveltekit-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-tanstack-start-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-vite-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-swc-playground	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-tarballs	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-web	Ready	Preview, v0	Aug 25, 2026 10:13pm

1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
workflow-docs	Skipped	v0	Aug 25, 2026 10:13pm

[github-actions]

🧪 E2E Test Results

❌ Some tests failed

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

python-node (8 failed):

• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP | 🔍 observability
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG | 🔍 observability
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8 | 🔍 observability
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR | 🔍 observability
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8 | 🔍 observability
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ | 🔍 observability
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R | 🔍 observability
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W | 🔍 observability

🌐 Cross-language Conformance (9 failed)

python (9 failed):

• deploymentId: 'latest' is a no-op in non-Vercel worlds | wrun_01M0XFVJ4Q5N1HH8PZ8PNMZJGM
• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W

⚠️ 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.

• addTenWorkflow (nitro)
• deploymentId: 'latest' is a no-op in non-Vercel worlds (nest)
• promiseAllWorkflow (tanstack-start)

🛠 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.

36 infra events

• cold-start-warmup · suite warmup (tanstack-start) · at 22:12:44Z · abandoned wrun_01M0XFPDAXWJQ7SD4FCKWQZYRA
• run-pickup-stall · readableStreamWorkflow (nuxt) · at 22:13:10Z · abandoned wrun_01M0XFQJSYN1EQ26EFWPB3FX7R
• cold-start-warmup · suite warmup (python) · at 22:13:14Z · abandoned wrun_41M0XFMGBW0GW4N24MJB4H7RZ2 · (+7 more)
• run-pickup-stall · promiseAllWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5680GKBWE9XG0BBRZ9M
• run-pickup-stall · nullByteWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56G0GGHTT01RVT5ZPQR
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56D0GGXH8CCPSM3Z9K0
• run-pickup-stall · sleepingWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56C0GNDC6T0ZY9S0GWJ
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5FK0GT4GR0302EQNF4C
• cold-start-warmup · suite warmup (python) · at 22:13:50Z · abandoned wrun_01M0XFNKQ582S72PXQHAGBHJWF · (+7 more)
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:14:03Z · abandoned wrun_41M0XFS5AQ0GQYVWX4P4E6BHBP
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VG6MYP4JCRF0YND76P
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VHYJRWT478MJQ5ATEM
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VPDWD6VRV31BCMBYKY
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VR3R0PYV37K2YVRRRT
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VS4X2AZC5TRBB4JGXA
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0FH0GMQFFRGHVXJJ4Z8
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0HP0GSMD2Y4Y5A9Z9YN
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KQ0GSSSERV48EGPZSX
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KW0GG34XF8JV5G9XBZ
• run-pickup-stall · spawnWorkflowFromStepWorkflow - spawning a child workflow using start() inside a step (nuxt) · at 22:14:36Z · abandoned wrun_01M0XFT6K1JSH0VSC613AMTMGZ
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FJRBBQF23Q3566PCDC
• run-pickup-stall · nullByteWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FKN4FY46S8NDW7FZC3
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FD12ZSSQN6DBYV3TYQ
• run-pickup-stall · sleepingWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FHR4YF1YXKYJEBBFF8
• run-pickup-stall · promiseAllWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FFR71T5MAHWFM1Q4XZ
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:15:21Z · abandoned wrun_41M0XFT4Y30GMP0Z8BB64YMFJV
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY33ZDAP24JG416SA097
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3AQJN5VYNF0Q0J4EWH
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3EYEP30QARW9VV86X7
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEHZ4Q2CVSNNP7Z9KYH
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEJ4WZR29NMCBTBKBQ3
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 22:16:56Z · abandoned wrun_01M0XFYFBN0RT2K0DG7ZMKDBMN
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 22:17:00Z · abandoned wrun_01M0XFYK9380895PK345J1CJ1D
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:17:02Z · abandoned wrun_41M0XFWWTM0GJJ8E84Y8DP0DJN
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:03Z · abandoned wrun_41M0XFWRC40GSMR0C35G2N42CZ
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:05Z · abandoned wrun_01M0XFYRPJNQB6GCV3QJYQ45M9

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
❌ ▲ Vercel Production	3570	8	742	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
❌ 🌐 Cross-language Conformance	0	9	132	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17053	17	2778	19848

Details by Category

❌ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
❌ python-node	0	8	152
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

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

❌ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
❌ python	0	9	132

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

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

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit f980c84 · Tue, 25 Aug 2026 22:35:16 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1289 (+30%) 🔻	1390 🔴 (+27%) 🔻	1423 🔴 (+26%) 🔻	1502 🔴 (+14%)	30
TTFS	stream	251 (-15%) 💚	1370 🔴 (+21%) 🔻	1390 🔴 (+21%) 🔻	1511 🔴 (+24%) 🔻	30
TTFS	hook + stream	1587 (+20%) 🔻	1724 🔴 (+19%) 🔻	1776 🔴 (+18%) 🔻	5891 🔴 (+283%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	652 (+5.8%)	2053 (+65%) 🔻	2209 (+18%) 🔻	2396 (+21%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	2103 (-2.0%)	4041 (+3.2%)	4273 (-33%) 💚	11906 (+45%) 🔻	10
STSO	1020 steps (inline)	121 (+17%) 🔻	161 (-12%)	178 (-15%)	236 (-72%) 💚	1019
WO	1020 steps	159955 (-15%)	159955 (-15%)	159955 (-15%)	159955 (-15%)	1
CRTT	first chunk (pooled)	119 (-2.5%)	183 (+11%)	212 (+9.8%)	329 (-18%) 💚	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	147 (+2%)	170 (-23%)	208 (-56%)	320 (-61%)	120 (-47%)	10
size sweep (100/s, 160B-12KB)	134 (-6%)	196 (-5%)	310 (+12%)	536 (+25%)	138 (-21%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	149 (-6%)	157 (-20%)	188 (-28%)	409 (-13%)	263 (-13%)	3
replay eve-gpt-5.6-sol-2000t (1x)	167 (+4%)	144 (-19%)	180 (-19%)	360 (-5%)	214 (-28%)	2
replay eve-gpt-5.6-sol-2000t (2x)	139 (-5%)	191 (-64%)	250 (-75%)	404 (-75%)	241 (-76%)	3

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

1020 steps (inline)

Cumulative STSO time: main 186880ms → this run 159772ms (Δ -27108ms, -15%)

100-150 ms █░░░░░░░░░░┃ main 40 this 434 +394
150-200 ms ███████████████┃████████ main 841 this 557 -284
200-250 ms ┃██ main 104 this 21 -83
250-300 ms ┃ main 17 this 3 -14
300-350 ms ┃ main 0 this 4 +4
350-400 ms ┃ main 2 this 0 -2
400-450 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
800-850 ms ┃ main 2 this 0 -2
850-900 ms ┃ main 10 this 0 -10
900-950 ms ┃ main 1 this 0 -1

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

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▂█▁···· 142.1 (-17%) 136 (-5%) 208 (-56%) 320 (-61%) 3000
sweep ······▂█▂▁··· 149.8 (-10%) 133 (-14%) 310 (+12%) 536 (+25%) 3000
gw 1x ·····▁▃█▁▁··· 131.6 (-16%) 125 (-12%) 188 (-28%) 409 (-13%) 5295
eve 1x ·····▁▃█▁···· 126.6 (-17%) 117 (-15%) 180 (-19%) 360 (-5%) 5186
eve 2x ·····▁▁█▃···· 163.7 (-50%) 151 (-27%) 250 (-75%) 404 (-75%) 7779

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

control █▅▄▄▃▃▄▃▁▄ 126–162ms
sweep █▃▅▆▂▃█▇▄▁ 130–168ms
gw 1x ▃▃▆▅▂▄█▅█▁ 121–143ms
eve 1x ▄▂▄▄▂▂▆█▃▁ 115–151ms
eve 2x ▅▂▄▃▁▅▇█▆▄ 132–196ms

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

sweep ▅█▆▄▁▁▁ 148–153ms

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

control ▁▅▄▇▇▄█▃▂▃ 38–47ms
sweep ▁▂▆▇▃▆█▅▆▃ 43–67ms
gw 1x ▂▃▃▁▃▄█▅▄▂ 35–48ms
eve 1x ▅▄▃▅▄▇██▄▁ 21–25ms
eve 2x █▆▅▄▄▇▄▁▄▅ 21–29ms

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-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 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.}

[VaguelySerious]

AI review: blocking issues found

[VaguelySerious]

LGTM assuming e2e passes (except python)

[TooTallNate]

AI: Approved. I found no blocking issues in the attribute-retention changes relative to the stacked #3604 base.

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.5 KiB (±0)	1.76 MiB (-106 B)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	763.2 KiB (+353 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.

f980c84 · run

[github-actions]

No backport to stable for 82e2678 (AI decision).

This commit extends the retained-VM optimization to cover workflow attribute writes, making attribute suspensions retainable (new generation guard for attribute signals, no_step_driver becomes no_replay_driver). It is a performance enhancement to an existing optimization path, not a fix for a correctness, crash, or data-loss defect on stable, and it changes when a live VM is resumed versus cold-replayed — behavior risk a maintenance line should not take on. The patch changeset does not make it a stability fix.

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

82e267893917e06f5d3ce316baefc27cd024a912

[NathanColosimo]

Summary

• retain the workflow VM across workflow attribute writes
• generation-guard attribute suspension signals
• keep waits on the cold-replay path

Verification

• pnpm --filter @workflow/core... build
• pnpm --filter @workflow/core test
• pnpm --filter @workflow/core typecheck
• focused Biome check (existing complexity warnings only)

[changeset-bot]

🦋 Changeset detected

Latest commit: f980c84

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

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[vercel]

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

Project	Deployment	Actions	Updated (UTC)
example-nextjs-workflow-turbopack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-nextjs-workflow-webpack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-astro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-express-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-fastify-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-hono-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nestjs-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nitro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nuxt-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-python-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-sveltekit-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-tanstack-start-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-vite-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-swc-playground	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-tarballs	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-web	Ready	Preview, v0	Aug 25, 2026 10:13pm

1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
workflow-docs	Skipped	v0	Aug 25, 2026 10:13pm

[github-actions]

🧪 E2E Test Results

❌ Some tests failed

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

python-node (8 failed):

• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP | 🔍 observability
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG | 🔍 observability
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8 | 🔍 observability
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR | 🔍 observability
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8 | 🔍 observability
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ | 🔍 observability
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R | 🔍 observability
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W | 🔍 observability

🌐 Cross-language Conformance (9 failed)

python (9 failed):

• deploymentId: 'latest' is a no-op in non-Vercel worlds | wrun_01M0XFVJ4Q5N1HH8PZ8PNMZJGM
• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W

⚠️ 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.

• addTenWorkflow (nitro)
• deploymentId: 'latest' is a no-op in non-Vercel worlds (nest)
• promiseAllWorkflow (tanstack-start)

🛠 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.

36 infra events

• cold-start-warmup · suite warmup (tanstack-start) · at 22:12:44Z · abandoned wrun_01M0XFPDAXWJQ7SD4FCKWQZYRA
• run-pickup-stall · readableStreamWorkflow (nuxt) · at 22:13:10Z · abandoned wrun_01M0XFQJSYN1EQ26EFWPB3FX7R
• cold-start-warmup · suite warmup (python) · at 22:13:14Z · abandoned wrun_41M0XFMGBW0GW4N24MJB4H7RZ2 · (+7 more)
• run-pickup-stall · promiseAllWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5680GKBWE9XG0BBRZ9M
• run-pickup-stall · nullByteWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56G0GGHTT01RVT5ZPQR
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56D0GGXH8CCPSM3Z9K0
• run-pickup-stall · sleepingWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56C0GNDC6T0ZY9S0GWJ
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5FK0GT4GR0302EQNF4C
• cold-start-warmup · suite warmup (python) · at 22:13:50Z · abandoned wrun_01M0XFNKQ582S72PXQHAGBHJWF · (+7 more)
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:14:03Z · abandoned wrun_41M0XFS5AQ0GQYVWX4P4E6BHBP
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VG6MYP4JCRF0YND76P
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VHYJRWT478MJQ5ATEM
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VPDWD6VRV31BCMBYKY
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VR3R0PYV37K2YVRRRT
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VS4X2AZC5TRBB4JGXA
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0FH0GMQFFRGHVXJJ4Z8
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0HP0GSMD2Y4Y5A9Z9YN
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KQ0GSSSERV48EGPZSX
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KW0GG34XF8JV5G9XBZ
• run-pickup-stall · spawnWorkflowFromStepWorkflow - spawning a child workflow using start() inside a step (nuxt) · at 22:14:36Z · abandoned wrun_01M0XFT6K1JSH0VSC613AMTMGZ
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FJRBBQF23Q3566PCDC
• run-pickup-stall · nullByteWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FKN4FY46S8NDW7FZC3
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FD12ZSSQN6DBYV3TYQ
• run-pickup-stall · sleepingWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FHR4YF1YXKYJEBBFF8
• run-pickup-stall · promiseAllWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FFR71T5MAHWFM1Q4XZ
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:15:21Z · abandoned wrun_41M0XFT4Y30GMP0Z8BB64YMFJV
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY33ZDAP24JG416SA097
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3AQJN5VYNF0Q0J4EWH
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3EYEP30QARW9VV86X7
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEHZ4Q2CVSNNP7Z9KYH
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEJ4WZR29NMCBTBKBQ3
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 22:16:56Z · abandoned wrun_01M0XFYFBN0RT2K0DG7ZMKDBMN
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 22:17:00Z · abandoned wrun_01M0XFYK9380895PK345J1CJ1D
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:17:02Z · abandoned wrun_41M0XFWWTM0GJJ8E84Y8DP0DJN
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:03Z · abandoned wrun_41M0XFWRC40GSMR0C35G2N42CZ
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:05Z · abandoned wrun_01M0XFYRPJNQB6GCV3QJYQ45M9

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
❌ ▲ Vercel Production	3570	8	742	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
❌ 🌐 Cross-language Conformance	0	9	132	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17053	17	2778	19848

Details by Category

❌ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
❌ python-node	0	8	152
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

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

❌ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
❌ python	0	9	132

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

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

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit f980c84 · Tue, 25 Aug 2026 22:35:16 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1289 (+30%) 🔻	1390 🔴 (+27%) 🔻	1423 🔴 (+26%) 🔻	1502 🔴 (+14%)	30
TTFS	stream	251 (-15%) 💚	1370 🔴 (+21%) 🔻	1390 🔴 (+21%) 🔻	1511 🔴 (+24%) 🔻	30
TTFS	hook + stream	1587 (+20%) 🔻	1724 🔴 (+19%) 🔻	1776 🔴 (+18%) 🔻	5891 🔴 (+283%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	652 (+5.8%)	2053 (+65%) 🔻	2209 (+18%) 🔻	2396 (+21%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	2103 (-2.0%)	4041 (+3.2%)	4273 (-33%) 💚	11906 (+45%) 🔻	10
STSO	1020 steps (inline)	121 (+17%) 🔻	161 (-12%)	178 (-15%)	236 (-72%) 💚	1019
WO	1020 steps	159955 (-15%)	159955 (-15%)	159955 (-15%)	159955 (-15%)	1
CRTT	first chunk (pooled)	119 (-2.5%)	183 (+11%)	212 (+9.8%)	329 (-18%) 💚	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	147 (+2%)	170 (-23%)	208 (-56%)	320 (-61%)	120 (-47%)	10
size sweep (100/s, 160B-12KB)	134 (-6%)	196 (-5%)	310 (+12%)	536 (+25%)	138 (-21%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	149 (-6%)	157 (-20%)	188 (-28%)	409 (-13%)	263 (-13%)	3
replay eve-gpt-5.6-sol-2000t (1x)	167 (+4%)	144 (-19%)	180 (-19%)	360 (-5%)	214 (-28%)	2
replay eve-gpt-5.6-sol-2000t (2x)	139 (-5%)	191 (-64%)	250 (-75%)	404 (-75%)	241 (-76%)	3

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

1020 steps (inline)

Cumulative STSO time: main 186880ms → this run 159772ms (Δ -27108ms, -15%)

100-150 ms █░░░░░░░░░░┃ main 40 this 434 +394
150-200 ms ███████████████┃████████ main 841 this 557 -284
200-250 ms ┃██ main 104 this 21 -83
250-300 ms ┃ main 17 this 3 -14
300-350 ms ┃ main 0 this 4 +4
350-400 ms ┃ main 2 this 0 -2
400-450 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
800-850 ms ┃ main 2 this 0 -2
850-900 ms ┃ main 10 this 0 -10
900-950 ms ┃ main 1 this 0 -1

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

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▂█▁···· 142.1 (-17%) 136 (-5%) 208 (-56%) 320 (-61%) 3000
sweep ······▂█▂▁··· 149.8 (-10%) 133 (-14%) 310 (+12%) 536 (+25%) 3000
gw 1x ·····▁▃█▁▁··· 131.6 (-16%) 125 (-12%) 188 (-28%) 409 (-13%) 5295
eve 1x ·····▁▃█▁···· 126.6 (-17%) 117 (-15%) 180 (-19%) 360 (-5%) 5186
eve 2x ·····▁▁█▃···· 163.7 (-50%) 151 (-27%) 250 (-75%) 404 (-75%) 7779

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

control █▅▄▄▃▃▄▃▁▄ 126–162ms
sweep █▃▅▆▂▃█▇▄▁ 130–168ms
gw 1x ▃▃▆▅▂▄█▅█▁ 121–143ms
eve 1x ▄▂▄▄▂▂▆█▃▁ 115–151ms
eve 2x ▅▂▄▃▁▅▇█▆▄ 132–196ms

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

sweep ▅█▆▄▁▁▁ 148–153ms

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

control ▁▅▄▇▇▄█▃▂▃ 38–47ms
sweep ▁▂▆▇▃▆█▅▆▃ 43–67ms
gw 1x ▂▃▃▁▃▄█▅▄▂ 35–48ms
eve 1x ▅▄▃▅▄▇██▄▁ 21–25ms
eve 2x █▆▅▄▄▇▄▁▄▅ 21–29ms

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-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 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.}

[VaguelySerious]

AI review: blocking issues found

[VaguelySerious]

LGTM assuming e2e passes (except python)

[TooTallNate]

AI: Approved. I found no blocking issues in the attribute-retention changes relative to the stacked #3604 base.

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.5 KiB (±0)	1.76 MiB (-106 B)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	763.2 KiB (+353 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.

f980c84 · run

[github-actions]

No backport to stable for 82e2678 (AI decision).

This commit extends the retained-VM optimization to cover workflow attribute writes, making attribute suspensions retainable (new generation guard for attribute signals, no_step_driver becomes no_replay_driver). It is a performance enhancement to an existing optimization path, not a fix for a correctness, crash, or data-loss defect on stable, and it changes when a live VM is resumed versus cold-replayed — behavior risk a maintenance line should not take on. The patch changeset does not make it a stability fix.

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

82e267893917e06f5d3ce316baefc27cd024a912

[NathanColosimo]

Summary

• retain the workflow VM across workflow attribute writes
• generation-guard attribute suspension signals
• keep waits on the cold-replay path

Verification

• pnpm --filter @workflow/core... build
• pnpm --filter @workflow/core test
• pnpm --filter @workflow/core typecheck
• focused Biome check (existing complexity warnings only)

[changeset-bot]

🦋 Changeset detected

Latest commit: f980c84

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]

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

Project	Deployment	Actions	Updated (UTC)
example-nextjs-workflow-turbopack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-nextjs-workflow-webpack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-astro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-express-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-fastify-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-hono-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nestjs-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nitro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nuxt-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-python-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-sveltekit-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-tanstack-start-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-vite-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-swc-playground	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-tarballs	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-web	Ready	Preview, v0	Aug 25, 2026 10:13pm

1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
workflow-docs	Skipped	v0	Aug 25, 2026 10:13pm

[github-actions]

🧪 E2E Test Results

❌ Some tests failed

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

python-node (8 failed):

• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP | 🔍 observability
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG | 🔍 observability
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8 | 🔍 observability
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR | 🔍 observability
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8 | 🔍 observability
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ | 🔍 observability
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R | 🔍 observability
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W | 🔍 observability

🌐 Cross-language Conformance (9 failed)

python (9 failed):

• deploymentId: 'latest' is a no-op in non-Vercel worlds | wrun_01M0XFVJ4Q5N1HH8PZ8PNMZJGM
• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W

⚠️ 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.

• addTenWorkflow (nitro)
• deploymentId: 'latest' is a no-op in non-Vercel worlds (nest)
• promiseAllWorkflow (tanstack-start)

🛠 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.

36 infra events

• cold-start-warmup · suite warmup (tanstack-start) · at 22:12:44Z · abandoned wrun_01M0XFPDAXWJQ7SD4FCKWQZYRA
• run-pickup-stall · readableStreamWorkflow (nuxt) · at 22:13:10Z · abandoned wrun_01M0XFQJSYN1EQ26EFWPB3FX7R
• cold-start-warmup · suite warmup (python) · at 22:13:14Z · abandoned wrun_41M0XFMGBW0GW4N24MJB4H7RZ2 · (+7 more)
• run-pickup-stall · promiseAllWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5680GKBWE9XG0BBRZ9M
• run-pickup-stall · nullByteWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56G0GGHTT01RVT5ZPQR
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56D0GGXH8CCPSM3Z9K0
• run-pickup-stall · sleepingWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56C0GNDC6T0ZY9S0GWJ
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5FK0GT4GR0302EQNF4C
• cold-start-warmup · suite warmup (python) · at 22:13:50Z · abandoned wrun_01M0XFNKQ582S72PXQHAGBHJWF · (+7 more)
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:14:03Z · abandoned wrun_41M0XFS5AQ0GQYVWX4P4E6BHBP
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VG6MYP4JCRF0YND76P
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VHYJRWT478MJQ5ATEM
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VPDWD6VRV31BCMBYKY
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VR3R0PYV37K2YVRRRT
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VS4X2AZC5TRBB4JGXA
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0FH0GMQFFRGHVXJJ4Z8
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0HP0GSMD2Y4Y5A9Z9YN
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KQ0GSSSERV48EGPZSX
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KW0GG34XF8JV5G9XBZ
• run-pickup-stall · spawnWorkflowFromStepWorkflow - spawning a child workflow using start() inside a step (nuxt) · at 22:14:36Z · abandoned wrun_01M0XFT6K1JSH0VSC613AMTMGZ
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FJRBBQF23Q3566PCDC
• run-pickup-stall · nullByteWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FKN4FY46S8NDW7FZC3
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FD12ZSSQN6DBYV3TYQ
• run-pickup-stall · sleepingWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FHR4YF1YXKYJEBBFF8
• run-pickup-stall · promiseAllWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FFR71T5MAHWFM1Q4XZ
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:15:21Z · abandoned wrun_41M0XFT4Y30GMP0Z8BB64YMFJV
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY33ZDAP24JG416SA097
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3AQJN5VYNF0Q0J4EWH
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3EYEP30QARW9VV86X7
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEHZ4Q2CVSNNP7Z9KYH
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEJ4WZR29NMCBTBKBQ3
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 22:16:56Z · abandoned wrun_01M0XFYFBN0RT2K0DG7ZMKDBMN
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 22:17:00Z · abandoned wrun_01M0XFYK9380895PK345J1CJ1D
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:17:02Z · abandoned wrun_41M0XFWWTM0GJJ8E84Y8DP0DJN
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:03Z · abandoned wrun_41M0XFWRC40GSMR0C35G2N42CZ
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:05Z · abandoned wrun_01M0XFYRPJNQB6GCV3QJYQ45M9

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
❌ ▲ Vercel Production	3570	8	742	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
❌ 🌐 Cross-language Conformance	0	9	132	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17053	17	2778	19848

Details by Category

❌ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
❌ python-node	0	8	152
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

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

❌ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
❌ python	0	9	132

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

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

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit f980c84 · Tue, 25 Aug 2026 22:35:16 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1289 (+30%) 🔻	1390 🔴 (+27%) 🔻	1423 🔴 (+26%) 🔻	1502 🔴 (+14%)	30
TTFS	stream	251 (-15%) 💚	1370 🔴 (+21%) 🔻	1390 🔴 (+21%) 🔻	1511 🔴 (+24%) 🔻	30
TTFS	hook + stream	1587 (+20%) 🔻	1724 🔴 (+19%) 🔻	1776 🔴 (+18%) 🔻	5891 🔴 (+283%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	652 (+5.8%)	2053 (+65%) 🔻	2209 (+18%) 🔻	2396 (+21%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	2103 (-2.0%)	4041 (+3.2%)	4273 (-33%) 💚	11906 (+45%) 🔻	10
STSO	1020 steps (inline)	121 (+17%) 🔻	161 (-12%)	178 (-15%)	236 (-72%) 💚	1019
WO	1020 steps	159955 (-15%)	159955 (-15%)	159955 (-15%)	159955 (-15%)	1
CRTT	first chunk (pooled)	119 (-2.5%)	183 (+11%)	212 (+9.8%)	329 (-18%) 💚	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	147 (+2%)	170 (-23%)	208 (-56%)	320 (-61%)	120 (-47%)	10
size sweep (100/s, 160B-12KB)	134 (-6%)	196 (-5%)	310 (+12%)	536 (+25%)	138 (-21%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	149 (-6%)	157 (-20%)	188 (-28%)	409 (-13%)	263 (-13%)	3
replay eve-gpt-5.6-sol-2000t (1x)	167 (+4%)	144 (-19%)	180 (-19%)	360 (-5%)	214 (-28%)	2
replay eve-gpt-5.6-sol-2000t (2x)	139 (-5%)	191 (-64%)	250 (-75%)	404 (-75%)	241 (-76%)	3

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

1020 steps (inline)

Cumulative STSO time: main 186880ms → this run 159772ms (Δ -27108ms, -15%)

100-150 ms █░░░░░░░░░░┃ main 40 this 434 +394
150-200 ms ███████████████┃████████ main 841 this 557 -284
200-250 ms ┃██ main 104 this 21 -83
250-300 ms ┃ main 17 this 3 -14
300-350 ms ┃ main 0 this 4 +4
350-400 ms ┃ main 2 this 0 -2
400-450 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
800-850 ms ┃ main 2 this 0 -2
850-900 ms ┃ main 10 this 0 -10
900-950 ms ┃ main 1 this 0 -1

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

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▂█▁···· 142.1 (-17%) 136 (-5%) 208 (-56%) 320 (-61%) 3000
sweep ······▂█▂▁··· 149.8 (-10%) 133 (-14%) 310 (+12%) 536 (+25%) 3000
gw 1x ·····▁▃█▁▁··· 131.6 (-16%) 125 (-12%) 188 (-28%) 409 (-13%) 5295
eve 1x ·····▁▃█▁···· 126.6 (-17%) 117 (-15%) 180 (-19%) 360 (-5%) 5186
eve 2x ·····▁▁█▃···· 163.7 (-50%) 151 (-27%) 250 (-75%) 404 (-75%) 7779

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

control █▅▄▄▃▃▄▃▁▄ 126–162ms
sweep █▃▅▆▂▃█▇▄▁ 130–168ms
gw 1x ▃▃▆▅▂▄█▅█▁ 121–143ms
eve 1x ▄▂▄▄▂▂▆█▃▁ 115–151ms
eve 2x ▅▂▄▃▁▅▇█▆▄ 132–196ms

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

sweep ▅█▆▄▁▁▁ 148–153ms

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

control ▁▅▄▇▇▄█▃▂▃ 38–47ms
sweep ▁▂▆▇▃▆█▅▆▃ 43–67ms
gw 1x ▂▃▃▁▃▄█▅▄▂ 35–48ms
eve 1x ▅▄▃▅▄▇██▄▁ 21–25ms
eve 2x █▆▅▄▄▇▄▁▄▅ 21–29ms

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-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 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.}

[VaguelySerious]

AI review: blocking issues found

[VaguelySerious]

LGTM assuming e2e passes (except python)

[TooTallNate]

AI: Approved. I found no blocking issues in the attribute-retention changes relative to the stacked #3604 base.

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.5 KiB (±0)	1.76 MiB (-106 B)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	763.2 KiB (+353 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.

f980c84 · run

[github-actions]

No backport to stable for 82e2678 (AI decision).

This commit extends the retained-VM optimization to cover workflow attribute writes, making attribute suspensions retainable (new generation guard for attribute signals, no_step_driver becomes no_replay_driver). It is a performance enhancement to an existing optimization path, not a fix for a correctness, crash, or data-loss defect on stable, and it changes when a live VM is resumed versus cold-replayed — behavior risk a maintenance line should not take on. The patch changeset does not make it a stability fix.

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

82e267893917e06f5d3ce316baefc27cd024a912

[NathanColosimo]

Summary

• retain the workflow VM across workflow attribute writes
• generation-guard attribute suspension signals
• keep waits on the cold-replay path

Verification

• pnpm --filter @workflow/core... build
• pnpm --filter @workflow/core test
• pnpm --filter @workflow/core typecheck
• focused Biome check (existing complexity warnings only)

[changeset-bot]

🦋 Changeset detected

Latest commit: f980c84

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]

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

Project	Deployment	Actions	Updated (UTC)
example-nextjs-workflow-turbopack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-nextjs-workflow-webpack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-astro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-express-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-fastify-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-hono-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nestjs-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nitro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nuxt-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-python-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-sveltekit-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-tanstack-start-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-vite-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-swc-playground	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-tarballs	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-web	Ready	Preview, v0	Aug 25, 2026 10:13pm

1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
workflow-docs	Skipped	v0	Aug 25, 2026 10:13pm

[github-actions]

🧪 E2E Test Results

❌ Some tests failed

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

python-node (8 failed):

• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP | 🔍 observability
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG | 🔍 observability
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8 | 🔍 observability
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR | 🔍 observability
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8 | 🔍 observability
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ | 🔍 observability
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R | 🔍 observability
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W | 🔍 observability

🌐 Cross-language Conformance (9 failed)

python (9 failed):

• deploymentId: 'latest' is a no-op in non-Vercel worlds | wrun_01M0XFVJ4Q5N1HH8PZ8PNMZJGM
• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W

⚠️ 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.

• addTenWorkflow (nitro)
• deploymentId: 'latest' is a no-op in non-Vercel worlds (nest)
• promiseAllWorkflow (tanstack-start)

🛠 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.

36 infra events

• cold-start-warmup · suite warmup (tanstack-start) · at 22:12:44Z · abandoned wrun_01M0XFPDAXWJQ7SD4FCKWQZYRA
• run-pickup-stall · readableStreamWorkflow (nuxt) · at 22:13:10Z · abandoned wrun_01M0XFQJSYN1EQ26EFWPB3FX7R
• cold-start-warmup · suite warmup (python) · at 22:13:14Z · abandoned wrun_41M0XFMGBW0GW4N24MJB4H7RZ2 · (+7 more)
• run-pickup-stall · promiseAllWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5680GKBWE9XG0BBRZ9M
• run-pickup-stall · nullByteWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56G0GGHTT01RVT5ZPQR
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56D0GGXH8CCPSM3Z9K0
• run-pickup-stall · sleepingWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56C0GNDC6T0ZY9S0GWJ
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5FK0GT4GR0302EQNF4C
• cold-start-warmup · suite warmup (python) · at 22:13:50Z · abandoned wrun_01M0XFNKQ582S72PXQHAGBHJWF · (+7 more)
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:14:03Z · abandoned wrun_41M0XFS5AQ0GQYVWX4P4E6BHBP
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VG6MYP4JCRF0YND76P
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VHYJRWT478MJQ5ATEM
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VPDWD6VRV31BCMBYKY
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VR3R0PYV37K2YVRRRT
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VS4X2AZC5TRBB4JGXA
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0FH0GMQFFRGHVXJJ4Z8
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0HP0GSMD2Y4Y5A9Z9YN
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KQ0GSSSERV48EGPZSX
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KW0GG34XF8JV5G9XBZ
• run-pickup-stall · spawnWorkflowFromStepWorkflow - spawning a child workflow using start() inside a step (nuxt) · at 22:14:36Z · abandoned wrun_01M0XFT6K1JSH0VSC613AMTMGZ
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FJRBBQF23Q3566PCDC
• run-pickup-stall · nullByteWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FKN4FY46S8NDW7FZC3
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FD12ZSSQN6DBYV3TYQ
• run-pickup-stall · sleepingWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FHR4YF1YXKYJEBBFF8
• run-pickup-stall · promiseAllWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FFR71T5MAHWFM1Q4XZ
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:15:21Z · abandoned wrun_41M0XFT4Y30GMP0Z8BB64YMFJV
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY33ZDAP24JG416SA097
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3AQJN5VYNF0Q0J4EWH
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3EYEP30QARW9VV86X7
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEHZ4Q2CVSNNP7Z9KYH
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEJ4WZR29NMCBTBKBQ3
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 22:16:56Z · abandoned wrun_01M0XFYFBN0RT2K0DG7ZMKDBMN
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 22:17:00Z · abandoned wrun_01M0XFYK9380895PK345J1CJ1D
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:17:02Z · abandoned wrun_41M0XFWWTM0GJJ8E84Y8DP0DJN
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:03Z · abandoned wrun_41M0XFWRC40GSMR0C35G2N42CZ
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:05Z · abandoned wrun_01M0XFYRPJNQB6GCV3QJYQ45M9

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
❌ ▲ Vercel Production	3570	8	742	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
❌ 🌐 Cross-language Conformance	0	9	132	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17053	17	2778	19848

Details by Category

❌ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
❌ python-node	0	8	152
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

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

❌ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
❌ python	0	9	132

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

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

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit f980c84 · Tue, 25 Aug 2026 22:35:16 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1289 (+30%) 🔻	1390 🔴 (+27%) 🔻	1423 🔴 (+26%) 🔻	1502 🔴 (+14%)	30
TTFS	stream	251 (-15%) 💚	1370 🔴 (+21%) 🔻	1390 🔴 (+21%) 🔻	1511 🔴 (+24%) 🔻	30
TTFS	hook + stream	1587 (+20%) 🔻	1724 🔴 (+19%) 🔻	1776 🔴 (+18%) 🔻	5891 🔴 (+283%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	652 (+5.8%)	2053 (+65%) 🔻	2209 (+18%) 🔻	2396 (+21%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	2103 (-2.0%)	4041 (+3.2%)	4273 (-33%) 💚	11906 (+45%) 🔻	10
STSO	1020 steps (inline)	121 (+17%) 🔻	161 (-12%)	178 (-15%)	236 (-72%) 💚	1019
WO	1020 steps	159955 (-15%)	159955 (-15%)	159955 (-15%)	159955 (-15%)	1
CRTT	first chunk (pooled)	119 (-2.5%)	183 (+11%)	212 (+9.8%)	329 (-18%) 💚	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	147 (+2%)	170 (-23%)	208 (-56%)	320 (-61%)	120 (-47%)	10
size sweep (100/s, 160B-12KB)	134 (-6%)	196 (-5%)	310 (+12%)	536 (+25%)	138 (-21%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	149 (-6%)	157 (-20%)	188 (-28%)	409 (-13%)	263 (-13%)	3
replay eve-gpt-5.6-sol-2000t (1x)	167 (+4%)	144 (-19%)	180 (-19%)	360 (-5%)	214 (-28%)	2
replay eve-gpt-5.6-sol-2000t (2x)	139 (-5%)	191 (-64%)	250 (-75%)	404 (-75%)	241 (-76%)	3

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

1020 steps (inline)

Cumulative STSO time: main 186880ms → this run 159772ms (Δ -27108ms, -15%)

100-150 ms █░░░░░░░░░░┃ main 40 this 434 +394
150-200 ms ███████████████┃████████ main 841 this 557 -284
200-250 ms ┃██ main 104 this 21 -83
250-300 ms ┃ main 17 this 3 -14
300-350 ms ┃ main 0 this 4 +4
350-400 ms ┃ main 2 this 0 -2
400-450 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
800-850 ms ┃ main 2 this 0 -2
850-900 ms ┃ main 10 this 0 -10
900-950 ms ┃ main 1 this 0 -1

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

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▂█▁···· 142.1 (-17%) 136 (-5%) 208 (-56%) 320 (-61%) 3000
sweep ······▂█▂▁··· 149.8 (-10%) 133 (-14%) 310 (+12%) 536 (+25%) 3000
gw 1x ·····▁▃█▁▁··· 131.6 (-16%) 125 (-12%) 188 (-28%) 409 (-13%) 5295
eve 1x ·····▁▃█▁···· 126.6 (-17%) 117 (-15%) 180 (-19%) 360 (-5%) 5186
eve 2x ·····▁▁█▃···· 163.7 (-50%) 151 (-27%) 250 (-75%) 404 (-75%) 7779

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

control █▅▄▄▃▃▄▃▁▄ 126–162ms
sweep █▃▅▆▂▃█▇▄▁ 130–168ms
gw 1x ▃▃▆▅▂▄█▅█▁ 121–143ms
eve 1x ▄▂▄▄▂▂▆█▃▁ 115–151ms
eve 2x ▅▂▄▃▁▅▇█▆▄ 132–196ms

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

sweep ▅█▆▄▁▁▁ 148–153ms

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

control ▁▅▄▇▇▄█▃▂▃ 38–47ms
sweep ▁▂▆▇▃▆█▅▆▃ 43–67ms
gw 1x ▂▃▃▁▃▄█▅▄▂ 35–48ms
eve 1x ▅▄▃▅▄▇██▄▁ 21–25ms
eve 2x █▆▅▄▄▇▄▁▄▅ 21–29ms

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-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 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.}

[VaguelySerious]

AI review: blocking issues found

[VaguelySerious]

LGTM assuming e2e passes (except python)

[TooTallNate]

AI: Approved. I found no blocking issues in the attribute-retention changes relative to the stacked #3604 base.

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.5 KiB (±0)	1.76 MiB (-106 B)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	763.2 KiB (+353 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.

f980c84 · run

[github-actions]

No backport to stable for 82e2678 (AI decision).

This commit extends the retained-VM optimization to cover workflow attribute writes, making attribute suspensions retainable (new generation guard for attribute signals, no_step_driver becomes no_replay_driver). It is a performance enhancement to an existing optimization path, not a fix for a correctness, crash, or data-loss defect on stable, and it changes when a live VM is resumed versus cold-replayed — behavior risk a maintenance line should not take on. The patch changeset does not make it a stability fix.

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

82e267893917e06f5d3ce316baefc27cd024a912

[NathanColosimo]

Summary

• retain the workflow VM across workflow attribute writes
• generation-guard attribute suspension signals
• keep waits on the cold-replay path

Verification

• pnpm --filter @workflow/core... build
• pnpm --filter @workflow/core test
• pnpm --filter @workflow/core typecheck
• focused Biome check (existing complexity warnings only)

[changeset-bot]

🦋 Changeset detected

Latest commit: f980c84

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]

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

Project	Deployment	Actions	Updated (UTC)
example-nextjs-workflow-turbopack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-nextjs-workflow-webpack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-astro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-express-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-fastify-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-hono-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nestjs-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nitro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nuxt-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-python-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-sveltekit-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-tanstack-start-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-vite-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-swc-playground	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-tarballs	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-web	Ready	Preview, v0	Aug 25, 2026 10:13pm

1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
workflow-docs	Skipped	v0	Aug 25, 2026 10:13pm

[github-actions]

🧪 E2E Test Results

❌ Some tests failed

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

python-node (8 failed):

• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP | 🔍 observability
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG | 🔍 observability
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8 | 🔍 observability
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR | 🔍 observability
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8 | 🔍 observability
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ | 🔍 observability
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R | 🔍 observability
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W | 🔍 observability

🌐 Cross-language Conformance (9 failed)

python (9 failed):

• deploymentId: 'latest' is a no-op in non-Vercel worlds | wrun_01M0XFVJ4Q5N1HH8PZ8PNMZJGM
• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W

⚠️ 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.

• addTenWorkflow (nitro)
• deploymentId: 'latest' is a no-op in non-Vercel worlds (nest)
• promiseAllWorkflow (tanstack-start)

🛠 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.

36 infra events

• cold-start-warmup · suite warmup (tanstack-start) · at 22:12:44Z · abandoned wrun_01M0XFPDAXWJQ7SD4FCKWQZYRA
• run-pickup-stall · readableStreamWorkflow (nuxt) · at 22:13:10Z · abandoned wrun_01M0XFQJSYN1EQ26EFWPB3FX7R
• cold-start-warmup · suite warmup (python) · at 22:13:14Z · abandoned wrun_41M0XFMGBW0GW4N24MJB4H7RZ2 · (+7 more)
• run-pickup-stall · promiseAllWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5680GKBWE9XG0BBRZ9M
• run-pickup-stall · nullByteWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56G0GGHTT01RVT5ZPQR
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56D0GGXH8CCPSM3Z9K0
• run-pickup-stall · sleepingWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56C0GNDC6T0ZY9S0GWJ
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5FK0GT4GR0302EQNF4C
• cold-start-warmup · suite warmup (python) · at 22:13:50Z · abandoned wrun_01M0XFNKQ582S72PXQHAGBHJWF · (+7 more)
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:14:03Z · abandoned wrun_41M0XFS5AQ0GQYVWX4P4E6BHBP
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VG6MYP4JCRF0YND76P
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VHYJRWT478MJQ5ATEM
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VPDWD6VRV31BCMBYKY
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VR3R0PYV37K2YVRRRT
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VS4X2AZC5TRBB4JGXA
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0FH0GMQFFRGHVXJJ4Z8
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0HP0GSMD2Y4Y5A9Z9YN
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KQ0GSSSERV48EGPZSX
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KW0GG34XF8JV5G9XBZ
• run-pickup-stall · spawnWorkflowFromStepWorkflow - spawning a child workflow using start() inside a step (nuxt) · at 22:14:36Z · abandoned wrun_01M0XFT6K1JSH0VSC613AMTMGZ
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FJRBBQF23Q3566PCDC
• run-pickup-stall · nullByteWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FKN4FY46S8NDW7FZC3
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FD12ZSSQN6DBYV3TYQ
• run-pickup-stall · sleepingWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FHR4YF1YXKYJEBBFF8
• run-pickup-stall · promiseAllWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FFR71T5MAHWFM1Q4XZ
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:15:21Z · abandoned wrun_41M0XFT4Y30GMP0Z8BB64YMFJV
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY33ZDAP24JG416SA097
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3AQJN5VYNF0Q0J4EWH
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3EYEP30QARW9VV86X7
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEHZ4Q2CVSNNP7Z9KYH
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEJ4WZR29NMCBTBKBQ3
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 22:16:56Z · abandoned wrun_01M0XFYFBN0RT2K0DG7ZMKDBMN
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 22:17:00Z · abandoned wrun_01M0XFYK9380895PK345J1CJ1D
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:17:02Z · abandoned wrun_41M0XFWWTM0GJJ8E84Y8DP0DJN
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:03Z · abandoned wrun_41M0XFWRC40GSMR0C35G2N42CZ
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:05Z · abandoned wrun_01M0XFYRPJNQB6GCV3QJYQ45M9

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
❌ ▲ Vercel Production	3570	8	742	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
❌ 🌐 Cross-language Conformance	0	9	132	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17053	17	2778	19848

Details by Category

❌ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
❌ python-node	0	8	152
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

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

❌ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
❌ python	0	9	132

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

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

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit f980c84 · Tue, 25 Aug 2026 22:35:16 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1289 (+30%) 🔻	1390 🔴 (+27%) 🔻	1423 🔴 (+26%) 🔻	1502 🔴 (+14%)	30
TTFS	stream	251 (-15%) 💚	1370 🔴 (+21%) 🔻	1390 🔴 (+21%) 🔻	1511 🔴 (+24%) 🔻	30
TTFS	hook + stream	1587 (+20%) 🔻	1724 🔴 (+19%) 🔻	1776 🔴 (+18%) 🔻	5891 🔴 (+283%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	652 (+5.8%)	2053 (+65%) 🔻	2209 (+18%) 🔻	2396 (+21%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	2103 (-2.0%)	4041 (+3.2%)	4273 (-33%) 💚	11906 (+45%) 🔻	10
STSO	1020 steps (inline)	121 (+17%) 🔻	161 (-12%)	178 (-15%)	236 (-72%) 💚	1019
WO	1020 steps	159955 (-15%)	159955 (-15%)	159955 (-15%)	159955 (-15%)	1
CRTT	first chunk (pooled)	119 (-2.5%)	183 (+11%)	212 (+9.8%)	329 (-18%) 💚	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	147 (+2%)	170 (-23%)	208 (-56%)	320 (-61%)	120 (-47%)	10
size sweep (100/s, 160B-12KB)	134 (-6%)	196 (-5%)	310 (+12%)	536 (+25%)	138 (-21%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	149 (-6%)	157 (-20%)	188 (-28%)	409 (-13%)	263 (-13%)	3
replay eve-gpt-5.6-sol-2000t (1x)	167 (+4%)	144 (-19%)	180 (-19%)	360 (-5%)	214 (-28%)	2
replay eve-gpt-5.6-sol-2000t (2x)	139 (-5%)	191 (-64%)	250 (-75%)	404 (-75%)	241 (-76%)	3

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

1020 steps (inline)

Cumulative STSO time: main 186880ms → this run 159772ms (Δ -27108ms, -15%)

100-150 ms █░░░░░░░░░░┃ main 40 this 434 +394
150-200 ms ███████████████┃████████ main 841 this 557 -284
200-250 ms ┃██ main 104 this 21 -83
250-300 ms ┃ main 17 this 3 -14
300-350 ms ┃ main 0 this 4 +4
350-400 ms ┃ main 2 this 0 -2
400-450 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
800-850 ms ┃ main 2 this 0 -2
850-900 ms ┃ main 10 this 0 -10
900-950 ms ┃ main 1 this 0 -1

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

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▂█▁···· 142.1 (-17%) 136 (-5%) 208 (-56%) 320 (-61%) 3000
sweep ······▂█▂▁··· 149.8 (-10%) 133 (-14%) 310 (+12%) 536 (+25%) 3000
gw 1x ·····▁▃█▁▁··· 131.6 (-16%) 125 (-12%) 188 (-28%) 409 (-13%) 5295
eve 1x ·····▁▃█▁···· 126.6 (-17%) 117 (-15%) 180 (-19%) 360 (-5%) 5186
eve 2x ·····▁▁█▃···· 163.7 (-50%) 151 (-27%) 250 (-75%) 404 (-75%) 7779

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

control █▅▄▄▃▃▄▃▁▄ 126–162ms
sweep █▃▅▆▂▃█▇▄▁ 130–168ms
gw 1x ▃▃▆▅▂▄█▅█▁ 121–143ms
eve 1x ▄▂▄▄▂▂▆█▃▁ 115–151ms
eve 2x ▅▂▄▃▁▅▇█▆▄ 132–196ms

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

sweep ▅█▆▄▁▁▁ 148–153ms

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

control ▁▅▄▇▇▄█▃▂▃ 38–47ms
sweep ▁▂▆▇▃▆█▅▆▃ 43–67ms
gw 1x ▂▃▃▁▃▄█▅▄▂ 35–48ms
eve 1x ▅▄▃▅▄▇██▄▁ 21–25ms
eve 2x █▆▅▄▄▇▄▁▄▅ 21–29ms

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-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 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.}

[VaguelySerious]

AI review: blocking issues found

[VaguelySerious]

LGTM assuming e2e passes (except python)

[TooTallNate]

AI: Approved. I found no blocking issues in the attribute-retention changes relative to the stacked #3604 base.

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.5 KiB (±0)	1.76 MiB (-106 B)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	763.2 KiB (+353 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.

f980c84 · run

[github-actions]

No backport to stable for 82e2678 (AI decision).

This commit extends the retained-VM optimization to cover workflow attribute writes, making attribute suspensions retainable (new generation guard for attribute signals, no_step_driver becomes no_replay_driver). It is a performance enhancement to an existing optimization path, not a fix for a correctness, crash, or data-loss defect on stable, and it changes when a live VM is resumed versus cold-replayed — behavior risk a maintenance line should not take on. The patch changeset does not make it a stability fix.

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

82e267893917e06f5d3ce316baefc27cd024a912

[NathanColosimo]

Summary

• retain the workflow VM across workflow attribute writes
• generation-guard attribute suspension signals
• keep waits on the cold-replay path

Verification

• pnpm --filter @workflow/core... build
• pnpm --filter @workflow/core test
• pnpm --filter @workflow/core typecheck
• focused Biome check (existing complexity warnings only)

[changeset-bot]

🦋 Changeset detected

Latest commit: f980c84

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]

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

Project	Deployment	Actions	Updated (UTC)
example-nextjs-workflow-turbopack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-nextjs-workflow-webpack	Ready	Preview, v0	Aug 25, 2026 10:13pm
example-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-astro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-express-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-fastify-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-hono-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nestjs-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nitro-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-nuxt-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-python-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-sveltekit-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-tanstack-start-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workbench-vite-workflow	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-swc-playground	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-tarballs	Ready	Preview, v0	Aug 25, 2026 10:13pm
workflow-web	Ready	Preview, v0	Aug 25, 2026 10:13pm

1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
workflow-docs	Skipped	v0	Aug 25, 2026 10:13pm

[github-actions]

🧪 E2E Test Results

❌ Some tests failed

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

python-node (8 failed):

• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP | 🔍 observability
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG | 🔍 observability
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8 | 🔍 observability
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR | 🔍 observability
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8 | 🔍 observability
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ | 🔍 observability
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R | 🔍 observability
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W | 🔍 observability

🌐 Cross-language Conformance (9 failed)

python (9 failed):

• deploymentId: 'latest' is a no-op in non-Vercel worlds | wrun_01M0XFVJ4Q5N1HH8PZ8PNMZJGM
• promiseAllWorkflow | wrun_41M0XFN5PF0GYJ6G6SXYSGCKBP
• sleepingWorkflow | wrun_41M0XFNYK50GSETQ4D3R6F3RCG
• parallelSleepWorkflow | wrun_41M0XFNYPN0GMQNDY61H9M4HH8
• nullByteWorkflow | wrun_41M0XFP8SP0GHHJ2GNMTZAEWXR
• cancelRun - cancelling a running workflow | wrun_41M0XFTXA20GW06GCGP3KGMCT8
• cancelRun via CLI - cancelling a running workflow | wrun_41M0XFTY680GNF9TXAPN79ZSGZ
• sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0XFV8NQ0GZWRBKSMP7KM18R
• resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0XFVV990GS26KPE0P4HAF1W

⚠️ 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.

• addTenWorkflow (nitro)
• deploymentId: 'latest' is a no-op in non-Vercel worlds (nest)
• promiseAllWorkflow (tanstack-start)

🛠 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.

36 infra events

• cold-start-warmup · suite warmup (tanstack-start) · at 22:12:44Z · abandoned wrun_01M0XFPDAXWJQ7SD4FCKWQZYRA
• run-pickup-stall · readableStreamWorkflow (nuxt) · at 22:13:10Z · abandoned wrun_01M0XFQJSYN1EQ26EFWPB3FX7R
• cold-start-warmup · suite warmup (python) · at 22:13:14Z · abandoned wrun_41M0XFMGBW0GW4N24MJB4H7RZ2 · (+7 more)
• run-pickup-stall · promiseAllWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5680GKBWE9XG0BBRZ9M
• run-pickup-stall · nullByteWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56G0GGHTT01RVT5ZPQR
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56D0GGXH8CCPSM3Z9K0
• run-pickup-stall · sleepingWorkflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR56C0GNDC6T0ZY9S0GWJ
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:13:30Z · abandoned wrun_41M0XFR5FK0GT4GR0302EQNF4C
• cold-start-warmup · suite warmup (python) · at 22:13:50Z · abandoned wrun_01M0XFNKQ582S72PXQHAGBHJWF · (+7 more)
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:14:03Z · abandoned wrun_41M0XFS5AQ0GQYVWX4P4E6BHBP
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VG6MYP4JCRF0YND76P
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VHYJRWT478MJQ5ATEM
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VPDWD6VRV31BCMBYKY
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VR3R0PYV37K2YVRRRT
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:05Z · abandoned wrun_01M0XFS8VS4X2AZC5TRBB4JGXA
• run-pickup-stall · sleepingWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0FH0GMQFFRGHVXJJ4Z8
• run-pickup-stall · nullByteWorkflow (python) · at 22:14:30Z · abandoned wrun_41M0XFT0HP0GSMD2Y4Y5A9Z9YN
• run-pickup-stall · promiseAllWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KQ0GSSSERV48EGPZSX
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:31Z · abandoned wrun_41M0XFT0KW0GG34XF8JV5G9XBZ
• run-pickup-stall · spawnWorkflowFromStepWorkflow - spawning a child workflow using start() inside a step (nuxt) · at 22:14:36Z · abandoned wrun_01M0XFT6K1JSH0VSC613AMTMGZ
• run-pickup-stall · parallelSleepWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FJRBBQF23Q3566PCDC
• run-pickup-stall · nullByteWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FKN4FY46S8NDW7FZC3
• run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FD12ZSSQN6DBYV3TYQ
• run-pickup-stall · sleepingWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FHR4YF1YXKYJEBBFF8
• run-pickup-stall · promiseAllWorkflow (python) · at 22:15:05Z · abandoned wrun_01M0XFV3FFR71T5MAHWFM1Q4XZ
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:15:21Z · abandoned wrun_41M0XFT4Y30GMP0Z8BB64YMFJV
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY33ZDAP24JG416SA097
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3AQJN5VYNF0Q0J4EWH
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:16:05Z · abandoned wrun_01M0XFWY3EYEP30QARW9VV86X7
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEHZ4Q2CVSNNP7Z9KYH
• run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_01M0XFXVEJ4WZR29NMCBTBKBQ3
• run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 22:16:56Z · abandoned wrun_01M0XFYFBN0RT2K0DG7ZMKDBMN
• run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 22:17:00Z · abandoned wrun_01M0XFYK9380895PK345J1CJ1D
• run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:17:02Z · abandoned wrun_41M0XFWWTM0GJJ8E84Y8DP0DJN
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:03Z · abandoned wrun_41M0XFWRC40GSMR0C35G2N42CZ
• run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:17:05Z · abandoned wrun_01M0XFYRPJNQB6GCV3QJYQ45M9

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
❌ ▲ Vercel Production	3570	8	742	4320
✅ 💻 Local Development	3922	0	558	4480
✅ 📦 Local Production	3922	0	558	4480
✅ 🐘 Local Postgres	3922	0	558	4480
✅ 🪟 Windows	320	0	0	320
❌ 🌐 Cross-language Conformance	0	9	132	141
✅ vercel-http-transport	817	0	143	960
✅ vercel-multi-region	27	0	0	27
✅ vercel-ws-transport	553	0	87	640
Total	17053	17	2778	19848

Details by Category

❌ ▲ Vercel Production

App	Passed	Failed	Skipped
✅ astro-node	132	0	28
✅ astro-quickjs	132	0	28
✅ example-node	132	0	28
✅ example-quickjs	132	0	28
✅ express-node	132	0	28
✅ express-quickjs	132	0	28
✅ fastify-node	132	0	28
✅ fastify-quickjs	132	0	28
✅ hono-node	132	0	28
✅ hono-quickjs	132	0	28
✅ nest-node	132	0	28
✅ nest-quickjs	132	0	28
✅ nextjs-turbopack-node	157	0	3
✅ nextjs-turbopack-quickjs	157	0	3
✅ nextjs-webpack-node	157	0	3
✅ nextjs-webpack-quickjs	157	0	3
✅ nitro-node	132	0	28
✅ nitro-quickjs	132	0	28
✅ nuxt-node	132	0	28
✅ nuxt-quickjs	132	0	28
❌ python-node	0	8	152
✅ sveltekit-node	151	0	9
✅ sveltekit-quickjs	151	0	9
✅ tanstack-start-node	132	0	28
✅ tanstack-start-quickjs	132	0	28
✅ vite-node	132	0	28
✅ vite-quickjs	132	0	28

✅ 💻 Local Development

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 📦 Local Production

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🐘 Local Postgres

App	Passed	Failed	Skipped
✅ astro-stable-node	134	0	26
✅ astro-stable-quickjs	134	0	26
✅ express-stable-node	134	0	26
✅ express-stable-quickjs	134	0	26
✅ fastify-stable-node	134	0	26
✅ fastify-stable-quickjs	134	0	26
✅ hono-stable-node	134	0	26
✅ hono-stable-quickjs	134	0	26
✅ nest-stable-node	134	0	26
✅ nest-stable-quickjs	134	0	26
✅ nextjs-turbopack-canary-node	141	0	19
✅ nextjs-turbopack-canary-quickjs	141	0	19
✅ nextjs-turbopack-stable-node	160	0	0
✅ nextjs-turbopack-stable-quickjs	160	0	0
✅ nextjs-webpack-canary-node	141	0	19
✅ nextjs-webpack-canary-quickjs	141	0	19
✅ nextjs-webpack-stable-node	160	0	0
✅ nextjs-webpack-stable-quickjs	160	0	0
✅ nitro-stable-node	134	0	26
✅ nitro-stable-quickjs	134	0	26
✅ nuxt-stable-node	134	0	26
✅ nuxt-stable-quickjs	134	0	26
✅ sveltekit-stable-node	153	0	7
✅ sveltekit-stable-quickjs	153	0	7
✅ tanstack-start-node	134	0	26
✅ tanstack-start-quickjs	134	0	26
✅ vite-stable-node	134	0	26
✅ vite-stable-quickjs	134	0	26

✅ 🪟 Windows

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

❌ 🌐 Cross-language Conformance

App	Passed	Failed	Skipped
❌ python	0	9	132

✅ vercel-http-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ hono	132	0	28
✅ nextjs-turbopack	157	0	3
✅ nitro	132	0	28
✅ vite	132	0	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

App	Passed	Failed	Skipped
✅ example	132	0	28
✅ express	132	0	28
✅ nextjs-turbopack	157	0	3
✅ vite	132	0	28

---

📋 View full workflow run

[github-actions]

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

Full trace: world-sim.txt

[github-actions]

📊 Workflow Benchmarks

commit f980c84 · Tue, 25 Aug 2026 22:35:16 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1289 (+30%) 🔻	1390 🔴 (+27%) 🔻	1423 🔴 (+26%) 🔻	1502 🔴 (+14%)	30
TTFS	stream	251 (-15%) 💚	1370 🔴 (+21%) 🔻	1390 🔴 (+21%) 🔻	1511 🔴 (+24%) 🔻	30
TTFS	hook + stream	1587 (+20%) 🔻	1724 🔴 (+19%) 🔻	1776 🔴 (+18%) 🔻	5891 🔴 (+283%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	652 (+5.8%)	2053 (+65%) 🔻	2209 (+18%) 🔻	2396 (+21%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	2103 (-2.0%)	4041 (+3.2%)	4273 (-33%) 💚	11906 (+45%) 🔻	10
STSO	1020 steps (inline)	121 (+17%) 🔻	161 (-12%)	178 (-15%)	236 (-72%) 💚	1019
WO	1020 steps	159955 (-15%)	159955 (-15%)	159955 (-15%)	159955 (-15%)	1
CRTT	first chunk (pooled)	119 (-2.5%)	183 (+11%)	212 (+9.8%)	329 (-18%) 💚	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	147 (+2%)	170 (-23%)	208 (-56%)	320 (-61%)	120 (-47%)	10
size sweep (100/s, 160B-12KB)	134 (-6%)	196 (-5%)	310 (+12%)	536 (+25%)	138 (-21%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	149 (-6%)	157 (-20%)	188 (-28%)	409 (-13%)	263 (-13%)	3
replay eve-gpt-5.6-sol-2000t (1x)	167 (+4%)	144 (-19%)	180 (-19%)	360 (-5%)	214 (-28%)	2
replay eve-gpt-5.6-sol-2000t (2x)	139 (-5%)	191 (-64%)	250 (-75%)	404 (-75%)	241 (-76%)	3

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

1020 steps (inline)

Cumulative STSO time: main 186880ms → this run 159772ms (Δ -27108ms, -15%)

100-150 ms █░░░░░░░░░░┃ main 40 this 434 +394
150-200 ms ███████████████┃████████ main 841 this 557 -284
200-250 ms ┃██ main 104 this 21 -83
250-300 ms ┃ main 17 this 3 -14
300-350 ms ┃ main 0 this 4 +4
350-400 ms ┃ main 2 this 0 -2
400-450 ms ┃ main 1 this 0 -1
500-550 ms ┃ main 1 this 0 -1
800-850 ms ┃ main 2 this 0 -2
850-900 ms ┃ main 10 this 0 -10
900-950 ms ┃ main 1 this 0 -1

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

variant RTT 1ms→5s+ avg p50 p90 p99 n
control ······▂█▁···· 142.1 (-17%) 136 (-5%) 208 (-56%) 320 (-61%) 3000
sweep ······▂█▂▁··· 149.8 (-10%) 133 (-14%) 310 (+12%) 536 (+25%) 3000
gw 1x ·····▁▃█▁▁··· 131.6 (-16%) 125 (-12%) 188 (-28%) 409 (-13%) 5295
eve 1x ·····▁▃█▁···· 126.6 (-17%) 117 (-15%) 180 (-19%) 360 (-5%) 5186
eve 2x ·····▁▁█▃···· 163.7 (-50%) 151 (-27%) 250 (-75%) 404 (-75%) 7779

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

control █▅▄▄▃▃▄▃▁▄ 126–162ms
sweep █▃▅▆▂▃█▇▄▁ 130–168ms
gw 1x ▃▃▆▅▂▄█▅█▁ 121–143ms
eve 1x ▄▂▄▄▂▂▆█▃▁ 115–151ms
eve 2x ▅▂▄▃▁▅▇█▆▄ 132–196ms

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

sweep ▅█▆▄▁▁▁ 148–153ms

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

control ▁▅▄▇▇▄█▃▂▃ 38–47ms
sweep ▁▂▆▇▃▆█▅▆▃ 43–67ms
gw 1x ▂▃▃▁▃▄█▅▄▂ 35–48ms
eve 1x ▅▄▃▅▄▇██▄▁ 21–25ms
eve 2x █▆▅▄▄▇▄▁▄▅ 21–29ms

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-2000teaf22f5946e7c61f3c65c7006d550df180cfabd4e706254a09f22aec0cfb420d · gateway-gpt-5.4-nano-2000t6f24ac518b6b83ff1d0e85a5fe78230db192716d66a7fc6b2fe022752001d041}

_{🔴 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.}

[VaguelySerious]

AI review: blocking issues found

[VaguelySerious]

LGTM assuming e2e passes (except python)

[TooTallNate]

AI: Approved. I found no blocking issues in the attribute-retention changes relative to the stacked #3604 base.

[github-actions]

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.5 KiB (±0)	1.76 MiB (-106 B)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	763.2 KiB (+353 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.

f980c84 · run

[github-actions]

No backport to stable for 82e2678 (AI decision).

This commit extends the retained-VM optimization to cover workflow attribute writes, making attribute suspensions retainable (new generation guard for attribute signals, no_step_driver becomes no_replay_driver). It is a performance enhancement to an existing optimization path, not a fix for a correctness, crash, or data-loss defect on stable, and it changes when a live VM is resumed versus cold-replayed — behavior risk a maintenance line should not take on. The patch changeset does not make it a stability fix.

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

82e267893917e06f5d3ce316baefc27cd024a912