[core] Prepare replay payloads as event frames arrive by NathanColosimo · Pull Request #3548 · vercel/workflow

NathanColosimo · 2026-08-14T03:54:35Z

Summary

resolve the run key as soon as a deployment-bearing replay event arrives
start decrypting and decompressing each payload synchronously from the validated-frame observer, with natural response backpressure
keep one invocation-scoped cache of prepared payloads across fresh VMs
reuse immutable primitive values for successful results, errors, and hook payloads while rehydrating object graphs per VM
let ordered consumers await only the payloads they touch instead of delaying suspension on speculative preparation

Performance signal

The latest benchmark and previous behavior run were recorded on the original cumulative branch before this review split. Across those runs, inline STSO improved 4–20% at p75, 10–24% at p90, and 39–51% at p99; total 1020-step workflow overhead improved 7–23%.

Cold TTFS regressed in both runs, including the turbo control that does not preload or prepare replay events, so that signal is dominated by deployment cold-start variability. The benchmarked branch also contained the small tracing layer in #3523.

Stack

[world-vercel] Resume partial replay streams after validated events #3546 — replay stream recovery
[core] Decode replay payloads synchronously #3547 — synchronous replay decode
[core] Prepare replay payloads as event frames arrive #3548 — streamed replay preparation
[core] Trace fresh workflow replay phases #3523 — replay phase tracing
[core] Prune schema modules from workflow bundles #3550 — prune sandbox dependency graph
[workflow] Load per-source replay bundles #3551 — per-source lazy VM bundles

Validation

rebuilt @workflow/world and @workflow/core
focused replay cache, runtime helper, delivery-ordering, hook, and sleep suites
141 tests passed, with 2 expected failures

changeset-bot · 2026-08-14T03:54:39Z

🦋 Changeset detected

Latest commit: dd3ed77

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

This PR includes changesets to release 16 packages

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

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

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

vercel · 2026-08-14T03:54:53Z

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

Project	Deployment	Actions	Updated (UTC)
example-nextjs-workflow-turbopack	Ready	Preview	Aug 14, 2026 10:59pm
example-nextjs-workflow-webpack	Ready	Preview	Aug 14, 2026 10:59pm
example-workflow	Ready	Preview	Aug 14, 2026 10:59pm
workbench-astro-workflow	Ready	Preview	Aug 14, 2026 10:59pm
workbench-express-workflow	Ready	Preview	Aug 14, 2026 10:59pm
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workbench-nuxt-workflow	Ready	Preview	Aug 14, 2026 10:59pm
workbench-python-workflow	Error		Aug 14, 2026 10:59pm
workbench-sveltekit-workflow	Ready	Preview	Aug 14, 2026 10:59pm
workbench-tanstack-start-workflow	Ready	Preview	Aug 14, 2026 10:59pm
workbench-vite-workflow	Ready	Preview	Aug 14, 2026 10:59pm
workflow-docs	Ready	Preview, v0	Aug 14, 2026 10:59pm
workflow-swc-playground	Ready	Preview	Aug 14, 2026 10:59pm
workflow-tarballs	Ready	Preview	Aug 14, 2026 10:59pm
workflow-web	Ready	Preview	Aug 14, 2026 10:59pm

github-actions · 2026-08-14T03:54:53Z

🧪 E2E Test Results

❌ Some tests failed

❌ Failed E2E Tests

🪟 Windows (1 failed)

nextjs-turbopack-quickjs (1 failed):

parallelStepsThenWebhookWorkflow - no hook_conflict from same-tick replay race | wrun_41M018237S0GY5H02S4Q8RMGPG

E2E Test Summary

Summary

	Passed	Failed	Skipped	Total
✅ ▲ Vercel Production	3313	0	587	3900
✅ 💻 Local Development	3810	0	558	4368
✅ 📦 Local Production	3810	0	558	4368
✅ 🐘 Local Postgres	3810	0	558	4368
❌ 🪟 Windows	311	1	0	312
✅ vercel-multi-region	27	0	0	27
Total	15081	1	2261	17343

Details by Category

✅ ▲ Vercel Production

App	Passed	Skipped
✅ astro-node	128	28
✅ astro-quickjs	128	28
✅ example-node	128	28
✅ example-quickjs	128	28
✅ express-node	128	28
✅ express-quickjs	128	28
✅ fastify-node	128	28
✅ fastify-quickjs	128	28
✅ hono-node	128	28
✅ hono-quickjs	128	28
✅ nest-node	128	28
✅ nest-quickjs	128	28
✅ nextjs-turbopack-quickjs	153	3
✅ nextjs-webpack-node	153	3
✅ nextjs-webpack-quickjs	153	3
✅ nitro-node	128	28
✅ nitro-quickjs	128	28
✅ nuxt-node	128	28
✅ nuxt-quickjs	128	28
✅ sveltekit-node	147	9
✅ sveltekit-quickjs	147	9
✅ tanstack-start-node	128	28
✅ tanstack-start-quickjs	128	28
✅ vite-node	128	28
✅ vite-quickjs	128	28

✅ 💻 Local Development

App	Passed	Skipped
✅ astro-stable-node	130	26
✅ astro-stable-quickjs	130	26
✅ express-stable-node	130	26
✅ express-stable-quickjs	130	26
✅ fastify-stable-node	130	26
✅ fastify-stable-quickjs	130	26
✅ hono-stable-node	130	26
✅ hono-stable-quickjs	130	26
✅ nest-stable-node	130	26
✅ nest-stable-quickjs	130	26
✅ nextjs-turbopack-canary-node	137	19
✅ nextjs-turbopack-canary-quickjs	137	19
✅ nextjs-turbopack-stable-node	156	0
✅ nextjs-turbopack-stable-quickjs	156	0
✅ nextjs-webpack-canary-node	137	19
✅ nextjs-webpack-canary-quickjs	137	19
✅ nextjs-webpack-stable-node	156	0
✅ nextjs-webpack-stable-quickjs	156	0
✅ nitro-stable-node	130	26
✅ nitro-stable-quickjs	130	26
✅ nuxt-stable-node	130	26
✅ nuxt-stable-quickjs	130	26
✅ sveltekit-stable-node	149	7
✅ sveltekit-stable-quickjs	149	7
✅ tanstack-start-node	130	26
✅ tanstack-start-quickjs	130	26
✅ vite-stable-node	130	26
✅ vite-stable-quickjs	130	26

✅ 📦 Local Production

App	Passed	Skipped
✅ astro-stable-node	130	26
✅ astro-stable-quickjs	130	26
✅ express-stable-node	130	26
✅ express-stable-quickjs	130	26
✅ fastify-stable-node	130	26
✅ fastify-stable-quickjs	130	26
✅ hono-stable-node	130	26
✅ hono-stable-quickjs	130	26
✅ nest-stable-node	130	26
✅ nest-stable-quickjs	130	26
✅ nextjs-turbopack-canary-node	137	19
✅ nextjs-turbopack-canary-quickjs	137	19
✅ nextjs-turbopack-stable-node	156	0
✅ nextjs-turbopack-stable-quickjs	156	0
✅ nextjs-webpack-canary-node	137	19
✅ nextjs-webpack-canary-quickjs	137	19
✅ nextjs-webpack-stable-node	156	0
✅ nextjs-webpack-stable-quickjs	156	0
✅ nitro-stable-node	130	26
✅ nitro-stable-quickjs	130	26
✅ nuxt-stable-node	130	26
✅ nuxt-stable-quickjs	130	26
✅ sveltekit-stable-node	149	7
✅ sveltekit-stable-quickjs	149	7
✅ tanstack-start-node	130	26
✅ tanstack-start-quickjs	130	26
✅ vite-stable-node	130	26
✅ vite-stable-quickjs	130	26

✅ 🐘 Local Postgres

App	Passed	Skipped
✅ astro-stable-node	130	26
✅ astro-stable-quickjs	130	26
✅ express-stable-node	130	26
✅ express-stable-quickjs	130	26
✅ fastify-stable-node	130	26
✅ fastify-stable-quickjs	130	26
✅ hono-stable-node	130	26
✅ hono-stable-quickjs	130	26
✅ nest-stable-node	130	26
✅ nest-stable-quickjs	130	26
✅ nextjs-turbopack-canary-node	137	19
✅ nextjs-turbopack-canary-quickjs	137	19
✅ nextjs-turbopack-stable-node	156	0
✅ nextjs-turbopack-stable-quickjs	156	0
✅ nextjs-webpack-canary-node	137	19
✅ nextjs-webpack-canary-quickjs	137	19
✅ nextjs-webpack-stable-node	156	0
✅ nextjs-webpack-stable-quickjs	156	0
✅ nitro-stable-node	130	26
✅ nitro-stable-quickjs	130	26
✅ nuxt-stable-node	130	26
✅ nuxt-stable-quickjs	130	26
✅ sveltekit-stable-node	149	7
✅ sveltekit-stable-quickjs	149	7
✅ tanstack-start-node	130	26
✅ tanstack-start-quickjs	130	26
✅ vite-stable-node	130	26
✅ vite-stable-quickjs	130	26

❌ 🪟 Windows

App	Passed	Failed	Skipped
✅ nextjs-turbopack-node	156	0	0
❌ nextjs-turbopack-quickjs	155	1	0

✅ vercel-multi-region

App	Passed	Failed	Skipped
✅ nextjs-turbopack	27	0	0

📋 View full workflow run

github-actions · 2026-08-14T03:57:14Z

Sim World

Simulated world deterministic testing for races. Traces

🟠 Mint-ordered log — 3 fail of 41 total

log=mint-ordered · 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`	failed	9	1.0m	MISMATCH	1
❌ `in-flight-before-decision-counted`	failed	9	1.0m	MISMATCH	1
❌ `in-flight-after-decision`	failed	9	1.0m	MISMATCH	1
✅ `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-mint.txt

🟢 Append-only log — 0 fail of 41 total

log=append-only · 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-append-only.txt

github-actions · 2026-08-14T03:57:23Z

📊 Workflow Benchmarks

❌ The benchmark run for dd3ed77 failed. See the run logs for details.

Partial results from the failed run:

commit dd3ed77 · Fri, 14 Aug 2026 23:13:44 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1269 (+442%) 🔻	1374 🔴 (+21%) 🔻	1417 🔴 (+19%) 🔻	1806 🔴 (+1.4%)	30
TTFS	stream	1285 (+461%) 🔻	1349 🔴 (+24%) 🔻	1373 🔴 (+19%) 🔻	1563 🔴 (+2.7%)	30
TTFS	hook + stream	492 (+21%) 🔻	1711 🔴 (+25%) 🔻	1767 🔴 (+26%) 🔻	1908 🔴 (+23%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	8907 (-5.3%)	10797 (+3.4%)	10991 (-3.4%)	11098 (-70%) 💚	10
Fan-out TTLS	Promise.all(100 steps)	18288 (-4.2%)	24624 (+9.1%)	26486 (+14%)	26907 (-42%) 💚	10
STSO	1020 steps (inline)	111 (-22%) 💚	420 (-14%)	448 (-18%) 💚	570 (-20%) 💚	1019
WO	1020 steps	369409 (-17%) 💚	369409 (-17%) 💚	369409 (-17%) 💚	369409 (-17%) 💚	1

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

1020 steps (inline)

Cumulative STSO time: main 440013ms → this run 369226ms (Δ -70787ms, -16%)

  100-150 ms  ┃                         main   1  this   9    +8
  150-200 ms  ██┃                       main  33  this  34    +1
  200-250 ms  █░░┃                      main  15  this  44   +29
  250-300 ms  ████░░░░░░░░┃             main  49  this 144   +95
  300-350 ms  ████████████░░░░░░░░┃     main 129  this 229  +100
  350-400 ms  ████████░░░░░░░░░┃        main  90  this 195  +105
  400-450 ms  ████████████████████░░░┃  main 227  this 267   +40
  450-500 ms  ██████┃████████████████   main 260  this  73  -187
  500-550 ms  ┃███████████              main 128  this  11  -117
  550-600 ms  ┃███                      main  43  this   3   -40
  600-650 ms  ┃█                        main  18  this   1   -17
  650-700 ms  ┃                         main  11  this   2    -9
  700-750 ms  ┃                         main   6  this   0    -6
  750-800 ms  ┃                         main   2  this   1    -1
  800-850 ms  ┃                         main   3  this   0    -3
  850-900 ms  ┃                         main   2  this   3    +1
 950-1000 ms  ┃                         main   1  this   1    +0
1000-1050 ms  ┃                         main   0  this   1    +1
2050-2100 ms  ┃                         main   0  this   1    +1

📜 Previous results (4)

`85a9860`

Fri, 14 Aug 2026 21:51:31 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1409 (+103%) 🔻	1499 🔴 (+34%) 🔻	1541 🔴 (+35%) 🔻	1624 🔴 (+5.7%)	30
TTFS	stream	1357 (+31%) 🔻	1458 🔴 (+29%) 🔻	1478 🔴 (+29%) 🔻	1585 🔴 (+29%) 🔻	30
TTFS	hook + stream	1612 (+31%) 🔻	1827 🔴 (+34%) 🔻	1902 🔴 (+36%) 🔻	2138 🔴 (+14%)	30
Fan-out TTFS	Promise.all(100 steps)	9080 (-2.0%)	10604 (+2.5%)	14954 (+44%) 🔻	17586 (+61%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	17693 (-2.6%)	20509 (±0%)	27674 (+28%) 🔻	31201 (+26%) 🔻	10
STSO	1020 steps (inline)	130 (-15%) 💚	351 (-29%) 💚	430 (-21%) 💚	573 (-24%) 💚	1019
WO	1020 steps	302321 (-33%) 💚	302321 (-33%) 💚	302321 (-33%) 💚	302321 (-33%) 💚	1
SL	stream latency	101	176 🔴	213 🔴	408 🔴	30
SO	stream overhead (text)	130	263 🔴	355	449	30
SO	stream overhead (structured)	130	294 🔴	341	719	30

`184d506`

Fri, 14 Aug 2026 20:27:25 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1298 (+490%) 🔻	1368 🔴 (+23%) 🔻	1433 🔴 (+21%) 🔻	1701 🔴 (+42%) 🔻	30
TTFS	stream	1306 (+449%) 🔻	1354 🔴 (+21%) 🔻	1382 🔴 (+21%) 🔻	1394 🔴 (+12%)	30
TTFS	hook + stream	1551 (+213%) 🔻	1643 🔴 (+24%) 🔻	1678 🔴 (+21%) 🔻	2041 🔴 (+46%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	8064 (-11%)	12379 (+23%) 🔻	12795 (+25%) 🔻	14852 (+43%) 🔻	10
Fan-out TTLS	Promise.all(100 steps)	18179 (+3.0%)	26641 (+42%) 🔻	28712 (+53%) 🔻	29341 (+47%) 🔻	10
STSO	1020 steps (inline)	86 (-39%) 💚	408 (+93%) 🔻	450 (+89%) 🔻	698 (+93%) 🔻	1019
WO	1020 steps	372978 (+83%) 🔻	372978 (+83%) 🔻	372978 (+83%) 🔻	372978 (+83%) 🔻	1
SL	stream latency	79 (-18%) 💚	106 🔴 (-34%) 💚	119 🔴 (-37%) 💚	696 🔴 (+88%) 🔻	30
SO	stream overhead (text)	106 (-29%) 💚	169 (-32%) 💚	332 (-48%) 💚	431 (-76%) 💚	30
SO	stream overhead (structured)	106 (-31%) 💚	247 (-20%) 💚	277 (-26%) 💚	634 (-7.2%)	30

`7471e77`

Fri, 14 Aug 2026 07:24:27 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	262 (-31%) 💚	1406 🔴 (+26%) 🔻	1439 🔴 (+27%) 🔻	1455 🔴 (-5.0%)	30
TTFS	stream	177 (-82%) 💚	1403 🔴 (+33%) 🔻	1408 🔴 (+32%) 🔻	1452 🔴 (+31%) 🔻	30
TTFS	hook + stream	382 (-70%) 💚	1613 🔴 (+16%) 🔻	1661 🔴 (+16%) 🔻	1733 🔴 (+7.0%)	30
Fan-out TTFS	Promise.all(100 steps)	10421 (+17%) 🔻	10665 (+7.2%)	11022 (+9.3%)	11495 (-15%)	10
Fan-out TTLS	Promise.all(100 steps)	19275 (+9.1%)	19757 (+4.7%)	19987 (+5.2%)	20749 (-11%)	10
STSO	1020 steps (inline)	133 (+8.1%)	187 (-2.1%)	214 (-6.6%)	330 (-43%) 💚	1019
WO	1020 steps	184362 (-5.7%)	184362 (-5.7%)	184362 (-5.7%)	184362 (-5.7%)	1
SL	stream latency	105 (+33%) 🔻	160 🔴 (+45%) 🔻	181 🔴 (+40%) 🔻	284 🔴 (-17%) 💚	30
SO	stream overhead (text)	117 (+5.4%)	357 🔴 (+98%) 🔻	615 🔴 (+199%) 🔻	838 (+39%) 🔻	30
SO	stream overhead (structured)	129 (+34%) 🔻	530 🔴 (+240%) 🔻	694 🔴 (+316%) 🔻	1239 🔴 (+581%) 🔻	30

`294d4b7`

Fri, 14 Aug 2026 04:20:32 GMT · run logs

vercel / nextjs-turbopack

Metric	Scenario	Best (ms)	P75 (ms)	P90 (ms)	P99 (ms)	Samples
TTFS	step	1342 (+252%) 🔻	1476 🔴 (+32%) 🔻	1501 🔴 (+32%) 🔻	1824 🔴 (+19%) 🔻	30
TTFS	stream	391 (-61%) 💚	1415 🔴 (+34%) 🔻	1422 🔴 (+33%) 🔻	1465 🔴 (+32%) 🔻	30
TTFS	hook + stream	1610 (+26%) 🔻	1778 🔴 (+28%) 🔻	1853 🔴 (+30%) 🔻	1982 🔴 (+22%) 🔻	30
Fan-out TTFS	Promise.all(100 steps)	8985 (+0.8%)	9408 (-5.5%)	10314 (+2.3%)	14770 (+9.2%)	10
Fan-out TTLS	Promise.all(100 steps)	17418 (-1.4%)	18078 (-4.2%)	18865 (-0.7%)	24537 (+4.7%)	10
STSO	1020 steps (inline)	120 (-2.4%)	184 (-3.7%)	208 (-9.2%)	347 (-40%) 💚	1019
WO	1020 steps	180947 (-7.4%)	180947 (-7.4%)	180947 (-7.4%)	180947 (-7.4%)	1
SL	stream latency	100 (+27%) 🔻	133 🔴 (+21%) 🔻	148 🔴 (+15%)	352 🔴 (+2.6%)	30
SO	stream overhead (text)	123 (+11%)	206 (+14%)	252 (+22%) 🔻	1984 🔴 (+228%) 🔻	30
SO	stream overhead (structured)	111 (+16%) 🔻	188 (+21%) 🔻	199 (+19%) 🔻	214 (+18%) 🔻	30

ℹ️ Metric definitions & methodology

_{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.}

_{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)}

_{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.}

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NathanColosimo changed the title ~~Prepare replay payloads during event streaming~~ [core] Prepare replay payloads as event frames arrive Aug 14, 2026

This was referenced Aug 14, 2026

[world-vercel] Resume partial replay streams after validated events #3546

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[core] Trace fresh workflow replay phases #3523

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[core] Decode replay payloads synchronously #3547

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NathanColosimo added 7 commits August 14, 2026 15:56

Prepare replay payloads during event streaming

1999d9d

[core] Centralize replay event hydration

acb29a2

[core] Simplify replay payload caching

860cef1

[core] Name replay preparation states explicitly

802b412

[core] Key replay payloads by event

51bfad1

[core] Collapse replay cache state machinery

cb7f4bd

[core] Pass replay event loading options directly

dd3ed77

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[core] Prepare replay payloads as event frames arrive - #3548

[core] Prepare replay payloads as event frames arrive#3548
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