feat(streams): add WebSocket v1 client protocol contract by alangenfeld · Pull Request #3763 · vercel/workflow

alangenfeld · 2026-08-24T21:00:32Z

Summary & Motivation

Defines the workflow-stream-ws/v1 frame schemas and encoder in @workflow/world-vercel, versioned independently of the REST API and workflow spec so a framing or acknowledgement change needs a new endpoint rather than a spec bump. Nothing calls it yet.

Test Plan

Protocol tests added, including a byte-for-byte check against workflow-server's canonical frame fixture.

Signed-off-by: Alex Langenfeld <alex.langenfeld@vercel.com>

changeset-bot · 2026-08-24T21:00:36Z

🦋 Changeset detected

Latest commit: ac59df1

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

This PR includes changesets to release 17 packages

Name	Type
@workflow/world-vercel	Patch
@workflow/cli	Patch
@workflow/core	Patch
@workflow/web	Patch
workflow	Patch
@workflow/world-testing	Patch
@workflow/builders	Patch
@workflow/next	Patch
@workflow/nitro	Patch
@workflow/vitest	Patch
@workflow/web-shared	Patch
@workflow/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

github-actions · 2026-08-24T21:00:51Z

🧪 E2E Test Results

❌ Some tests failed

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

python-node (8 failed):

promiseAllWorkflow | wrun_41M0TX9M260GQZZSE6MFEN180K | 🔍 observability
sleepingWorkflow | wrun_41M0TXA9X50GGY770Y2EEHECAR | 🔍 observability
parallelSleepWorkflow | wrun_41M0TXABZS0GVK1BHSMNV17FQR | 🔍 observability
nullByteWorkflow | wrun_41M0TXAKNN0GYSH1708DP9T4A5 | 🔍 observability
cancelRun - cancelling a running workflow | wrun_41M0TXFFQ30GGM70CKK2XY24F4 | 🔍 observability
cancelRun via CLI - cancelling a running workflow | wrun_41M0TXFKEJ0GYZ7FSNCAWRQCAS | 🔍 observability
sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0TXFR9C0GYHNB4ARQHZPDEB | 🔍 observability
resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0TXGA9F0GWFQJVD83BA886Y | 🔍 observability

🌐 Cross-language Conformance (9 failed)

python (9 failed):

deploymentId: 'latest' is a no-op in non-Vercel worlds | wrun_01M0TXME3JN69YTB6KH14REXQ0
promiseAllWorkflow | wrun_41M0TX9M260GQZZSE6MFEN180K
sleepingWorkflow | wrun_41M0TXA9X50GGY770Y2EEHECAR
parallelSleepWorkflow | wrun_41M0TXABZS0GVK1BHSMNV17FQR
nullByteWorkflow | wrun_41M0TXAKNN0GYSH1708DP9T4A5
cancelRun - cancelling a running workflow | wrun_41M0TXFFQ30GGM70CKK2XY24F4
cancelRun via CLI - cancelling a running workflow | wrun_41M0TXFKEJ0GYZ7FSNCAWRQCAS
sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M0TXFR9C0GYHNB4ARQHZPDEB
resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M0TXGA9F0GWFQJVD83BA886Y

⚠️ 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 (fastify)
cancelRun via CLI - cancelling a running workflow (express)
cancelRun via CLI - cancelling a running workflow (fastify)
cancelRun via CLI - cancelling a running workflow (nextjs-turbopack)
cancelRun via CLI - cancelling a running workflow (sveltekit)
deploymentId: 'latest' is a no-op in non-Vercel worlds (nitro)
health check (CLI) - workflow health command reports healthy endpoints (nextjs-webpack)

🛠 Infra Events (absorbed by the harness)

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

33 infra events

cold-start-warmup · suite warmup (python) · at 22:14:27Z · abandoned wrun_41M0TXA19Q0GH1J3Y2EW9WG46F · (+7 more)
run-pickup-stall · nullByteWorkflow (python) · at 22:14:44Z · abandoned wrun_41M0TXDP100GT4XKXFXYV71DSH
run-pickup-stall · promiseAllWorkflow (python) · at 22:14:44Z · abandoned wrun_41M0TXDP0Q0GZYYA7ZDRGGJA68
run-pickup-stall · parallelSleepWorkflow (python) · at 22:14:44Z · abandoned wrun_41M0TXDP0W0GYH5W24RMBY21HV
run-pickup-stall · sleepingWorkflow (python) · at 22:14:44Z · abandoned wrun_41M0TXDP0W0GYH5W24RMBY21HT
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:14:44Z · abandoned wrun_41M0TXDPFC0GHW1V0180EMGDPR
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:15:17Z · abandoned wrun_41M0TXEPD20GX5YYYDG2CQ37J3
run-pickup-stall · parallelSleepWorkflow (python) · at 22:15:44Z · abandoned wrun_41M0TXFHGC0GSENEEXWFVA074Z
run-pickup-stall · sleepingWorkflow (python) · at 22:15:45Z · abandoned wrun_41M0TXFHKK0GP7MVBJZRZMFW32
run-pickup-stall · nullByteWorkflow (python) · at 22:15:45Z · abandoned wrun_41M0TXFHHF0GZDCYV0JJ01N4E1
run-pickup-stall · promiseAllWorkflow (python) · at 22:15:45Z · abandoned wrun_41M0TXFHSQ0GGJW6TZHDV15ATA
cold-start-warmup · suite warmup (tanstack-start) · at 22:15:52Z · abandoned wrun_01M0TXFDQZ8WXQDS9E45YEBYH6
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:16:35Z · abandoned wrun_41M0TXFPJ10GS2HW7Q867WQMZC
cold-start-warmup · suite warmup (python) · at 22:16:53Z · abandoned wrun_01M0TXEFP85TCPNYAYR8TY1Y40 · (+7 more)
run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:17:08Z · abandoned wrun_01M0TXJ4TFHJ86EGW0KGENRM7Y
run-pickup-stall · sleepingWorkflow (python) · at 22:17:08Z · abandoned wrun_01M0TXJ4TNGJGHK49GWZEAADDE
run-pickup-stall · nullByteWorkflow (python) · at 22:17:08Z · abandoned wrun_01M0TXJ4TSKRC6XB4EKDBKJN5B
run-pickup-stall · promiseAllWorkflow (python) · at 22:17:08Z · abandoned wrun_01M0TXJ4TGDZHWQN3N38ZK4YM6
run-pickup-stall · parallelSleepWorkflow (python) · at 22:17:08Z · abandoned wrun_01M0TXJ4TQVFVW4Q3680M4Y3YR
run-pickup-stall · promiseAllWorkflow (python) · at 22:18:08Z · abandoned wrun_01M0TXKZE8NZ2EHPBANV9CRQCG
run-pickup-stall · parallelSleepWorkflow (python) · at 22:18:08Z · abandoned wrun_01M0TXKZEBQ34X5H03SZ5CZ2W7
run-pickup-stall · sleepingWorkflow (python) · at 22:18:08Z · abandoned wrun_01M0TXKZEA1D0AC5J3JQJG0618
run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:18:08Z · abandoned wrun_01M0TXKZECF9BAPB2DV2VQYC0D
run-pickup-stall · nullByteWorkflow (python) · at 22:18:08Z · abandoned wrun_01M0TXKZEKNW5707N28P78J01A
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:18:16Z · abandoned wrun_41M0TXJEEJ0GY1C81002C4XBVW
run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:18:16Z · abandoned wrun_41M0TXJ9CZ0GHZRCHZRDGND5ZQ
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:19:08Z · abandoned wrun_01M0TXNT1ZX13ABFTBM4VXY9BY
run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:19:08Z · abandoned wrun_01M0TXNT24JHTDHTJV93DRHE35
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:19:08Z · abandoned wrun_01M0TXNT229W66AJBETF8B5G5Q
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:19:38Z · abandoned wrun_01M0TXPQDTHE4J5M8ZP7MFT3Q1
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:19:38Z · abandoned wrun_01M0TXPQDXG40MJAF3JHHXW6V1
run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:20:08Z · abandoned wrun_01M0TXQMN7M6AEASP0GQ565TYN
run-pickup-stall · hookWithSleepWorkflow - hook payloads delivered correctly with concurrent sleep (nextjs-webpack) · at 22:21:14Z · abandoned wrun_01M0TXSMZ7H5XH2W54KESZQV30

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

✅ 📦 Local Production

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

✅ 🐘 Local Postgres

App	Passed	Skipped
✅ astro-stable-node	134	26
✅ astro-stable-quickjs	134	26
✅ express-stable-node	134	26
✅ express-stable-quickjs	134	26
✅ fastify-stable-node	134	26
✅ fastify-stable-quickjs	134	26
✅ hono-stable-node	134	26
✅ hono-stable-quickjs	134	26
✅ nest-stable-node	134	26
✅ nest-stable-quickjs	134	26
✅ nextjs-turbopack-canary-node	141	19
✅ nextjs-turbopack-canary-quickjs	141	19
✅ nextjs-turbopack-stable-node	160	0
✅ nextjs-turbopack-stable-quickjs	160	0
✅ nextjs-webpack-canary-node	141	19
✅ nextjs-webpack-canary-quickjs	141	19
✅ nextjs-webpack-stable-node	160	0
✅ nextjs-webpack-stable-quickjs	160	0
✅ nitro-stable-node	134	26
✅ nitro-stable-quickjs	134	26
✅ nuxt-stable-node	134	26
✅ nuxt-stable-quickjs	134	26
✅ sveltekit-stable-node	153	7
✅ sveltekit-stable-quickjs	153	7
✅ tanstack-start-node	134	26
✅ tanstack-start-quickjs	134	26
✅ vite-stable-node	134	26
✅ vite-stable-quickjs	134	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	Skipped
✅ example	132	28
✅ express	132	28
✅ hono	132	28
✅ nextjs-turbopack	157	3
✅ nitro	132	28
✅ vite	132	28

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

✅ vercel-ws-transport

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

📋 View full workflow run

vercel · 2026-08-24T21:00:54Z

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 24, 2026 10:12pm
example-nextjs-workflow-webpack	Ready	Preview, v0	Aug 24, 2026 10:12pm
example-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-astro-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-express-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-fastify-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-hono-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-nestjs-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-nitro-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-nuxt-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-python-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-sveltekit-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-tanstack-start-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workbench-vite-workflow	Ready	Preview, v0	Aug 24, 2026 10:12pm
workflow-docs	Ready	Preview, v0	Aug 24, 2026 10:12pm
workflow-swc-playground	Ready	Preview, v0	Aug 24, 2026 10:12pm
workflow-tarballs	Ready	Preview, v0	Aug 24, 2026 10:12pm
workflow-web	Ready	Preview, v0	Aug 24, 2026 10:12pm

github-actions · 2026-08-24T21:00:54Z

📊 Workflow Benchmarks

commit ac59df1 · Mon, 24 Aug 2026 22:35:00 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1306 (+31%) 🔻	1392 🔴 (+26%) 🔻	1428 🔴 (+24%) 🔻	1461 🔴 (+17%) 🔻	30
TTFS	stream	351 (-50%) 💚	1360 🔴 (+24%) 🔻	1383 🔴 (+25%) 🔻	1489 🔴 (+16%) 🔻	30
TTFS	hook + stream	1219 (-11%)	1694 🔴 (+15%) 🔻	1731 🔴 (+15%)	5919 🔴 (+271%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	549 (-16%) 💚	1897 (+11%)	1944 (+8.7%)	2000 (+2.8%)	10
Fan-out TTLS	Promise.all(100 steps)	2183 (+13%)	4689 (+48%) 🔻	4731 (+44%) 🔻	9124 (+7.6%)	10
STSO	1020 steps (inline)	116 (+10%)	167 (+13%)	188 (+12%)	399 (+83%) 🔻	1019
WO	1020 steps	163048 (+10%)	163048 (+10%)	163048 (+10%)	163048 (+10%)	1
CRTT	first chunk (pooled)	104 (+18%) 🔻	161 (+30%) 🔻	197 (+2.1%)	351 (-43%) 💚	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	157 (+39%)	181 (+39%)	282 (+33%)	4380 (+475%)	176 (+23%)	10
size sweep (100/s, 160B-12KB)	118 (+4%)	163 (+15%)	233 (+25%)	740 (-34%)	122 (-11%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	112 (-9%)	694 (+6%)	3332 (+1%)	4864 (+2%)	465 (+114%)	3
replay eve-gpt-5.6-sol-2000t (1x)	133 (+13%)	127 (-5%)	160 (-5%)	300 (-13%)	235 (-10%)	2
replay eve-gpt-5.6-sol-2000t (2x)	170 (+38%)	171 (-7%)	230 (-13%)	457 (-17%)	193 (-15%)	3

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

1020 steps (inline)

Cumulative STSO time: main 147417ms → this run 162868ms (Δ +15451ms, +10%)

  100-150 ms  ████████████████┃███████  main 785  this 558  -227
  150-200 ms  ███████░░░░┃              main 216  this 382  +166
  200-250 ms  █┃                        main  14  this  51   +37
  250-300 ms  ┃                         main   4  this  11    +7
  300-350 ms  ┃                         main   0  this   4    +4
  350-400 ms  ┃                         main   0  this   3    +3
  400-450 ms  ┃                         main   0  this   3    +3
  450-500 ms  ┃                         main   0  this   1    +1
  500-550 ms  ┃                         main   0  this   3    +3
  700-750 ms  ┃                         main   0  this   1    +1
  850-900 ms  ┃                         main   0  this   1    +1
1050-1100 ms  ┃                         main   0  this   1    +1

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

variant  RTT 1ms→5s+              avg         p50         p90           p99     n
control  ······▃█▂·▁▂·  416.5 (+247%)  123 (+16%)  282 (+33%)  4380 (+475%)  3000
sweep    ······▃█▁▁···     141 (+14%)  122 (+11%)  233 (+25%)    740 (-34%)  3000
gw 1x    ·····▁▇█▁▁▁▁▁    344.8 (+3%)   103 (+2%)  3332 (+1%)    4864 (+2%)  5295
eve 1x   ·····▁▇█▁····    112.9 (+2%)  104 (+14%)   160 (-5%)    300 (-13%)  5186
eve 2x   ·····▁▃█▂▁···    137.6 (-2%)   130 (+1%)  230 (-13%)    457 (-17%)  7779

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

control  ▁██▇▆▅▅▄▃▃  249–537ms
sweep    ▅▄▃▃▁▁▂▄█▇  122–168ms
gw 1x    ▁▁▁▃█▅▂▁▁▁  102–1356ms
eve 1x   ▄▃▂▂▂▂█▇▁▂  102–135ms
eve 2x   ▂▁▃▁▁▃▅█▄▄  114–189ms

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

sweep  ▃▂▆█▇▅▁  139–142ms

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

control  █▂▁▃▁▂▂▁▁▁  39–100ms
sweep    ▁▃▆▅▅▆█▄▆▂  46–62ms
gw 1x    ▂▂▂█▁▁▂▂▁▁  29–65ms
eve 1x   ▄▅▁▁█▄█▄▅▇  20–25ms
eve 2x   ▆▇▄▁▄▆▆▃▄█  19–26ms

📜 Previous results (1)

`fdeae36`

Mon, 24 Aug 2026 21:28:37 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1316 (+32%) 🔻	1425 🔴 (+29%) 🔻	1476 🔴 (+28%) 🔻	1501 🔴 (+20%) 🔻	30
TTFS	stream	332 (-53%) 💚	1403 🔴 (+28%) 🔻	1480 🔴 (+34%) 🔻	1527 🔴 (+19%) 🔻	30
TTFS	hook + stream	1269 (-7.6%)	1648 🔴 (+12%)	1690 🔴 (+12%)	1752 🔴 (+9.8%)	30
Fan-out TTFS	Promise.all(100 steps)	648 (±0%)	1939 (+13%)	2000 (+12%)	2106 (+8.2%)	10
Fan-out TTLS	Promise.all(100 steps)	2017 (+4.4%)	3634 (+14%)	3657 (+11%)	8990 (+6.0%)	10
STSO	1020 steps (inline)	109 (+3.8%)	142 (-4.1%)	159 (-5.4%)	226 (+3.7%)	1019
WO	1020 steps	141034 (-4.4%)	141034 (-4.4%)	141034 (-4.4%)	141034 (-4.4%)	1
CRTT	first chunk (pooled)	110 (+25%) 🔻	174 (+40%) 🔻	345 (+79%) 🔻	401 (-35%) 💚	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	165 (+46%)	174 (+34%)	314 (+48%)	447 (-41%)	140 (-2%)	10
size sweep (100/s, 160B-12KB)	133 (+18%)	185 (+30%)	305 (+63%)	455 (-60%)	158 (+15%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	157 (+28%)	146 (-78%)	188 (-94%)	437 (-91%)	199 (-8%)	3
replay eve-gpt-5.6-sol-2000t (1x)	130 (+10%)	159 (+19%)	196 (+16%)	348 (+1%)	235 (-10%)	2
replay eve-gpt-5.6-sol-2000t (2x)	158 (+28%)	234 (+28%)	328 (+25%)	468 (-15%)	199 (-13%)	3

ℹ️ Metric definitions & methodology

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

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

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

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

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

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

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

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

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

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

github-actions · 2026-08-24T21:04:28Z

Sim World

Simulated world deterministic testing for races. Traces

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

fence=per-spec

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

Full trace: world-sim.txt

Signed-off-by: Alex Langenfeld <alex.langenfeld@vercel.com>

feat(streams): add WebSocket v1 client protocol contract

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test(streams): preserve fixture line endings

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feat(streams): add WebSocket v1 client protocol contract - #3763

feat(streams): add WebSocket v1 client protocol contract#3763
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🧪 E2E Test Results

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

🌐 Cross-language Conformance (9 failed)

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