feat(streams): add resumable WebSocket reads by alangenfeld · Pull Request #3864 · vercel/workflow

alangenfeld · 2026-08-27T21:15:19Z

Summary & Motivation

Streamer.streams.getResumable — an optional World reader that owns interruption recovery itself, so core's reconnecting readers hand off to it instead of stacking a second recovery owner on top.
WORKFLOW_STREAM_READS_TRANSPORT=ws opts world-vercel into the dedicated workflow-stream-read-ws/v1 reader, gated separately from stream writes so reads never share the writer socket.

Test Plan

Covered by new unit tests: the core handoff, the read gate, and traceparent injection on the read upgrade. Manual runs of the focused world-vercel and core suites passed; the root build is blocked locally by a missing Rust toolchain for the unrelated SWC plugin.

changeset-bot · 2026-08-27T21:15:25Z

🦋 Changeset detected

Latest commit: d361ea9

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

This PR includes changesets to release 20 packages

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

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

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

vercel · 2026-08-27T21:15:38Z

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 28, 2026 10:47pm
example-nextjs-workflow-webpack	Ready	Preview, v0	Aug 28, 2026 10:47pm
example-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-astro-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-express-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-fastify-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-hono-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-nestjs-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-nitro-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-nuxt-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-python-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-sveltekit-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-tanstack-start-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workbench-vite-workflow	Ready	Preview, v0	Aug 28, 2026 10:47pm
workflow-docs	Ready	Preview, v0	Aug 28, 2026 10:47pm
workflow-swc-playground	Ready	Preview, v0	Aug 28, 2026 10:47pm
workflow-tarballs	Ready	Preview, v0	Aug 28, 2026 10:47pm
workflow-web	Ready	Preview, v0	Aug 28, 2026 10:47pm

github-actions · 2026-08-27T21:17:52Z

🧪 E2E Test Results

❌ Some tests failed

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

python-node (8 failed):

promiseAllWorkflow | wrun_41M158TQ7H0GM16FBE1XGXQWEM | 🔍 observability
sleepingWorkflow | wrun_41M158VC9Z0GMPFF50HYX7W8A0 | 🔍 observability
parallelSleepWorkflow | wrun_41M158VCN50GM8612X5MSA7VES | 🔍 observability
nullByteWorkflow | wrun_41M158VKAH0GXCB92C83HYDCQY | 🔍 observability
cancelRun - cancelling a running workflow | wrun_41M158ZZ1A0GYR50FX6A2GAZ23 | 🔍 observability
cancelRun via CLI - cancelling a running workflow | wrun_41M159042A0GW09ZYC05SH961A | 🔍 observability
sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M1590AP40GR8MBVZ9XRBARDC | 🔍 observability
resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M1590TJM0GH7ZPEA0KWEGD0G | 🔍 observability

🌐 Cross-language Conformance (9 failed)

python (9 failed):

deploymentId: 'latest' is a no-op in non-Vercel worlds | wrun_01M1595EZ01K56PFBM8Y9G2BF3
promiseAllWorkflow | wrun_41M158TQ7H0GM16FBE1XGXQWEM
sleepingWorkflow | wrun_41M158VC9Z0GMPFF50HYX7W8A0
parallelSleepWorkflow | wrun_41M158VCN50GM8612X5MSA7VES
nullByteWorkflow | wrun_41M158VKAH0GXCB92C83HYDCQY
cancelRun - cancelling a running workflow | wrun_41M158ZZ1A0GYR50FX6A2GAZ23
cancelRun via CLI - cancelling a running workflow | wrun_41M159042A0GW09ZYC05SH961A
sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M1590AP40GR8MBVZ9XRBARDC
resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M1590TJM0GH7ZPEA0KWEGD0G

⚠️ 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)
cancelRun via CLI - cancelling a running workflow (astro)
cancelRun via CLI - cancelling a running workflow (nextjs-turbopack)
cancelRun via CLI - cancelling a running workflow (vite)
deploymentId: 'latest' is a no-op in non-Vercel worlds (express)
deploymentId: 'latest' is a no-op in non-Vercel worlds (nextjs-webpack)
hookWorkflow (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.

34 infra events

cold-start-warmup · suite warmup (python) · at 22:48:07Z · abandoned wrun_41M158TH4D0GM0BDH7PB4ZMPZW · (+7 more)
run-pickup-stall · nullByteWorkflow (python) · at 22:48:23Z · abandoned wrun_41M158Y67C0GYZQ255NQ6T6ZV6
run-pickup-stall · sleepingWorkflow (python) · at 22:48:23Z · abandoned wrun_41M158Y6780GSPJ489JN3D8XCZ
run-pickup-stall · promiseAllWorkflow (python) · at 22:48:23Z · abandoned wrun_41M158Y6730GSX2Y7FM7523V0E
run-pickup-stall · parallelSleepWorkflow (python) · at 22:48:23Z · abandoned wrun_41M158Y6780GSPJ489JN3D8XD0
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:48:24Z · abandoned wrun_41M158Y6NQ0GZF9A7RPHC2JJKZ
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:48:57Z · abandoned wrun_41M158Z6NV0GNM9QSFT9M23NHA
run-pickup-stall · sleepingWorkflow (python) · at 22:49:24Z · abandoned wrun_41M15901SW0GGHV76TTJDM4XH6
run-pickup-stall · promiseAllWorkflow (python) · at 22:49:24Z · abandoned wrun_41M15901VX0GNZHJZ2PWDNRTF0
run-pickup-stall · nullByteWorkflow (python) · at 22:49:24Z · abandoned wrun_41M15901Z30GZ94WDBZG36AXJ4
run-pickup-stall · parallelSleepWorkflow (python) · at 22:49:24Z · abandoned wrun_41M159024B0GSQ8W536RC3DDMP
cold-start-warmup · suite warmup (tanstack-start) · at 22:50:26Z · abandoned wrun_01M1591KE37F6Q6MHGSCY5FCVC
cold-start-warmup · suite warmup (python) · at 22:50:50Z · abandoned wrun_01M158ZGGT11FFPQEPZPAQXH7G · (+7 more)
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:50:55Z · abandoned wrun_41M15906X40GG2RZTNXVC92RDY
run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:51:05Z · abandoned wrun_01M15935NXQ0ERW7MB0NJJ650B
run-pickup-stall · sleepingWorkflow (python) · at 22:51:05Z · abandoned wrun_01M15935P3EQ97X9G7GJMC7DE4
run-pickup-stall · promiseAllWorkflow (python) · at 22:51:05Z · abandoned wrun_01M15935NY6RD97RHD8DEVNX79
run-pickup-stall · parallelSleepWorkflow (python) · at 22:51:05Z · abandoned wrun_01M15935P4KHHGY1A2KW0GS42Q
run-pickup-stall · nullByteWorkflow (python) · at 22:51:05Z · abandoned wrun_01M15935P6AYZRD856ZHC52YX8
run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:51:57Z · abandoned wrun_41M1592SPF0GY58Y8P1NCTA63Q
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:51:58Z · abandoned wrun_41M15925E00GQ5ZDG37C9HTP5V
run-pickup-stall · promiseAllWorkflow (python) · at 22:52:05Z · abandoned wrun_01M159509J8Y2NHY4S40A1MR0D
run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 22:52:05Z · abandoned wrun_01M159509P01R14J9KR5FRBCZ3
run-pickup-stall · parallelSleepWorkflow (python) · at 22:52:05Z · abandoned wrun_01M159509W382C0FQBW31EEJ26
run-pickup-stall · sleepingWorkflow (python) · at 22:52:05Z · abandoned wrun_01M159509VSPVSS6E9QA83Q33D
run-pickup-stall · nullByteWorkflow (python) · at 22:52:05Z · abandoned wrun_01M159509YW6PYFZDKJ3H3AG9F
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:53:05Z · abandoned wrun_01M1596TX3R8QGFW7WTPPP6K3A
run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:53:05Z · abandoned wrun_01M1596TXDPSX66A67ZMYYD0YB
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:53:05Z · abandoned wrun_01M1596TXBV46P7RN22J4WYTDV
run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 22:53:35Z · abandoned wrun_01M1597R8RPF41NRAV0NR0GJWV
run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 22:53:35Z · abandoned wrun_01M1597R8QEAA85FG4QNK68S4K
run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 22:54:05Z · abandoned wrun_01M1598NGG7WDRZ03VGQ5X1QT7
run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 22:55:05Z · abandoned wrun_01M159AFYPB21HSY0VKZ7YN9XN
run-pickup-stall · concurrent hook token conflict - two workflows cannot use the same hook token simultaneously (nextjs-webpack) · at 22:55:09Z · abandoned wrun_01M159AKQ6616NVBTSKA7WHR8E

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

github-actions · 2026-08-27T21:18:22Z

📊 Workflow Benchmarks

commit d361ea9 · Fri, 28 Aug 2026 23:01:52 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	225 (-67%) 💚	1231 🔴 (+8.6%)	1244 🔴 (+9.0%)	1254 🔴 (+8.9%)	30
TTFS	stream	198 (-14%)	1238 🔴 (+15%)	1257 🔴 (+14%)	1536 🔴 (+32%) 🔻	30
TTFS	hook + stream	1346 (+175%) 🔻	1481 🔴 (+9.9%)	1657 🔴 (+20%) 🔻	5836 🔴 (+301%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	542 (-3.7%)	844 (-51%) 💚	1963 (+8.1%)	2070 (+5.3%)	10
Fan-out TTLS	Promise.all(100 steps)	1780 (-19%) 💚	3676 (-0.9%)	3710 (-1.4%)	8311 (+5.6%)	10
STSO	1020 steps (inline)	111 (-1.8%)	137 (-2.1%)	158 (-1.9%)	531 (+170%) 🔻	1019
WO	1020 steps	146548 (+4.1%)	146548 (+4.1%)	146548 (+4.1%)	146548 (+4.1%)	1
CRTT	first chunk (pooled)	73 (-37%) 💚	111 (-53%) 💚	150 (-70%) 💚	203 (-69%) 💚	28

Streams

Scenario	CRTT 1st	p75	p90	p99	CDV max	iters
paced control (100/s, 60B)	106 (-26%)	116 (-77%)	144 (-80%)	235 (-76%)	112 (-75%)	10
size sweep (100/s, 160B-12KB)	90.5 (-49%)	121 (-48%)	224 (-60%)	389 (-57%)	110 (-53%)	10
replay gateway-gpt-5.4-nano-2000t (1x)	79 (-60%)	110 (-53%)	129 (-71%)	292 (-70%)	170 (-77%)	3
replay eve-gpt-5.6-sol-2000t (1x)	94.5 (-76%)	113 (-80%)	142 (-92%)	234 (-94%)	262 (-88%)	2
replay eve-gpt-5.6-sol-2000t (2x)	102 (-35%)	135 (-82%)	176 (-83%)	296 (-78%)	229 (-60%)	3

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

1020 steps (inline)

Cumulative STSO time: main 139837ms → this run 146374ms (Δ +6537ms, +5%)

  100-150 ms  ███████████████████████┃  main 857  this 865    +8
  150-200 ms  ██┃█                      main 152  this 117   -35
  200-250 ms  ┃                         main   8  this  16    +8
  250-300 ms  ┃                         main   0  this   5    +5
  300-350 ms  ┃                         main   2  this   2    +0
  350-400 ms  ┃                         main   0  this   1    +1
  450-500 ms  ┃                         main   0  this   2    +2
  500-550 ms  ┃                         main   0  this   1    +1
  700-750 ms  ┃                         main   0  this   1    +1
  750-800 ms  ┃                         main   0  this   1    +1
  800-850 ms  ┃                         main   0  this   2    +2
  850-900 ms  ┃                         main   0  this   1    +1
 950-1000 ms  ┃                         main   0  this   1    +1
1000-1050 ms  ┃                         main   0  this   1    +1
1200-1250 ms  ┃                         main   0  this   1    +1
1350-1400 ms  ┃                         main   0  this   1    +1
1850-1900 ms  ┃                         main   0  this   1    +1

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

variant  RTT 1ms→5s+             avg         p50         p90         p99     n
control  ·····▁█▇▁····  100.8 (-64%)   97 (-49%)  144 (-80%)  235 (-76%)  3000
sweep    ·····▁█▆▁····  104.3 (-50%)   93 (-46%)  224 (-60%)  389 (-57%)  3000
gw 1x    ·····▁█▄▁····   95.6 (-53%)   91 (-44%)  129 (-71%)  292 (-70%)  5295
eve 1x   ·····▁█▅▁····   96.3 (-77%)   90 (-51%)  142 (-92%)  234 (-94%)  5186
eve 2x   ·····▁▆█▁····  116.9 (-70%)  109 (-56%)  176 (-83%)  296 (-78%)  7779

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

control  █▅▇▅▁▆▂▅▁▄  94–108ms
sweep    ▃▅▅▃▆█▃▁▃▂  90–125ms
gw 1x    ▂█▄▂▃▆▂▄▁▃  87–111ms
eve 1x   ▃▁▆▇▃▄█▆▃▂  84–111ms
eve 2x   ▅▁▄▁▂▅▄█▄▃  101–144ms

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

sweep  ▆▇█▆▄▂▁  101–107ms

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

control  ▁▄▄▆▅▅█▆▃▂  26–36ms
sweep    ▂▁▅▆▆█▃▁▅▃  33–48ms
gw 1x    ▂█▅▁▅▇▄▆▃▆  22–31ms
eve 1x   ▂▁▄▃▁▂█▂▄▂  20–27ms
eve 2x   █▁▆▁▅▆▄▃▄▆  17–24ms

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 · 2026-08-27T21:18:51Z

Sim World

Simulated world deterministic testing for races. Traces

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

fence=per-spec

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

Full trace: world-sim.txt

github-actions · 2026-08-27T21:26:31Z

Framework	Flow route	Step reg.	Framework output
hono	200.9 KiB (±0)	40.3 KiB (-99 B)	1.77 MiB (+5.5 KiB)
nextjs-turbopack	206.3 KiB (±0)	439 B (±0)	768.1 KiB (+4.2 KiB)

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.

d361ea9 · run

vercel

Additional Suggestion:

The pre-open HTTP fallback in the resumable WS read session uses a raw single-shot HTTP body that trusts its own EOF and cannot reconnect, silently truncating (or spuriously erroring) object streams once WORKFLOW_STREAM_READS_TRANSPORT=ws disables the core reader's recovery safety net.

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

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feat(streams): add resumable WebSocket reads

d361ea9

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

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feat(streams): add resumable WebSocket reads - #3864

feat(streams): add resumable WebSocket reads#3864
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🧪 E2E Test Results

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

🌐 Cross-language Conformance (9 failed)

⚠️ Flaky E2E Tests (passed on retry)

🛠 Infra Events (absorbed by the harness)

E2E Test Summary

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📊 Workflow Benchmarks

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