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[core] Overlap workflow compilation with replay loading - #3798

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codex/speed-fresh-replayfrom
codex/replay-compile-overlap
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[core] Overlap workflow compilation with replay loading#3798
NathanColosimo wants to merge 2 commits into
codex/speed-fresh-replayfrom
codex/replay-compile-overlap

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@NathanColosimo

@NathanColosimo NathanColosimo commented Aug 25, 2026 •
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Summary

  • start the first-delivery run_started request before beginning speculative Node bundle compilation
  • overlap compilation with the in-flight replay setup request
  • replace a speculative compile when the authoritative returned workflow name differs
  • skip Node compilation for QuickJS
  • keep bundle evaluation inside each fresh VM after replay loading

workflow.bundle.compile and workflow.replay.load are sibling setup spans under workflow.execute. The workflow.run span begins afterward and contains fresh-VM context creation, bundle evaluation, input hydration, and replay execution.

Stack

Depends on #3797.

Validation

  • focused runtime tracing and setup suites passed at the stack tip
  • full @workflow/core suite passed at the stack tip — 2,295 tests
  • pnpm --filter @workflow/core typecheck
  • git diff --check

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🦋 Changeset detected

Latest commit: d1ab139

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

@NathanColosimo NathanColosimo mentioned this pull request Aug 25, 2026
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🧪 E2E Test Results

❌ Some tests failed

❌ Failed E2E Tests

▲ Vercel Production (8 failed)

python-node (8 failed):

  • promiseAllWorkflow | wrun_41M154APPP0GG2WAJ97ZG922DC | 🔍 observability
  • sleepingWorkflow | wrun_41M154BXQN0GN51RG8VJ97E0BH | 🔍 observability
  • parallelSleepWorkflow | wrun_41M154C6Q30GVK1VDQ37XH9D5Y | 🔍 observability
  • nullByteWorkflow | wrun_41M154CNJJ0GJ928E9ZC6T9SVX | 🔍 observability
  • cancelRun - cancelling a running workflow | wrun_41M154H5SH0GMD9X0H3K059KY5 | 🔍 observability
  • cancelRun via CLI - cancelling a running workflow | wrun_41M154HAB30GGQE3KPWEGTVQVZ | 🔍 observability
  • sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M154HFZ20GNS3Y9KFQ87W546 | 🔍 observability
  • resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M154J3WS0GMMY2864TSS0ASV | 🔍 observability

🌐 Cross-language Conformance (9 failed)

python (9 failed):

  • deploymentId: 'latest' is a no-op in non-Vercel worlds | wrun_01M154M0P5V03RZSFG1FXAZGDX
  • promiseAllWorkflow | wrun_41M154APPP0GG2WAJ97ZG922DC
  • sleepingWorkflow | wrun_41M154BXQN0GN51RG8VJ97E0BH
  • parallelSleepWorkflow | wrun_41M154C6Q30GVK1VDQ37XH9D5Y
  • nullByteWorkflow | wrun_41M154CNJJ0GJ928E9ZC6T9SVX
  • cancelRun - cancelling a running workflow | wrun_41M154H5SH0GMD9X0H3K059KY5
  • cancelRun via CLI - cancelling a running workflow | wrun_41M154HAB30GGQE3KPWEGTVQVZ
  • sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration | wrun_41M154HFZ20GNS3Y9KFQ87W546
  • resilient start: addTenWorkflow completes when run_created returns 500 | wrun_41M154J3WS0GMMY2864TSS0ASV

⚠️ 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.

13 flaky tests
  • addTenWorkflow (fastify)
  • addTenWorkflow (hono)
  • addTenWorkflow (nitro)
  • addTenWorkflow (nuxt)
  • addTenWorkflow (tanstack-start)
  • cancelRun via CLI - cancelling a running workflow (express)
  • hookWorkflow (astro)
  • hookWorkflow (express)
  • hookWorkflow (nest)
  • hookWorkflow (vite)
  • retainedInterleavingWorkflow (nextjs-turbopack)
  • RetryableError respects custom retryAfter delay (express)
  • stepWinsRaceWorkflow (fastify)

🛠 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 21:28:29Z · abandoned wrun_41M1548QHN0GMHMYHAZHDKGNKN · (+5 more)
  • run-pickup-stall · promiseAllWorkflow (python) · at 21:28:51Z · abandoned wrun_41M154CD1J0GTD2YV4D1MMD5KW
  • run-pickup-stall · parallelSleepWorkflow (python) · at 21:28:51Z · abandoned wrun_41M154CD1R0GZHS2VF09E2HKM1
  • run-pickup-stall · sleepingWorkflow (python) · at 21:28:52Z · abandoned wrun_41M154CD1R0GZHS2VF09E2HKM0
  • run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 21:28:53Z · abandoned wrun_41M154CGSA0GN24XZ7EFFQFMDC
  • run-pickup-stall · nullByteWorkflow (python) · at 21:28:53Z · abandoned wrun_41M154CD1W0GJQW99WP3X8NPCS
  • run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 21:29:27Z · abandoned wrun_41M154DM5K0GV0QT0JZG9MWHM4
  • run-pickup-stall · nullByteWorkflow (python) · at 21:29:47Z · abandoned wrun_41M154E8MS0GMFJ4RVF2VSVJF7
  • run-pickup-stall · promiseAllWorkflow (python) · at 21:29:47Z · abandoned wrun_41M154E8Q90GVM4NW6GSTC9X8J
  • run-pickup-stall · sleepingWorkflow (python) · at 21:29:47Z · abandoned wrun_41M154E8GW0GYPJ62WSS4PC236
  • run-pickup-stall · parallelSleepWorkflow (python) · at 21:29:47Z · abandoned wrun_41M154E8ZV0GNC2CJBB2T8A25D
  • cold-start-warmup · suite warmup (tanstack-start) · at 21:30:23Z · abandoned wrun_01M154F0VDRWCXPG3NNQKVW84M
  • run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 21:30:35Z · abandoned wrun_41M154EMPE0GM4FCXEJT8MM1JR
  • cold-start-warmup · suite warmup (python) · at 21:31:24Z · abandoned wrun_01M154E28DZ1EPKGBC084713DC · (+7 more)
  • run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 21:31:25Z · abandoned wrun_41M154G6GT0GNPXWT6NNBC7F6M
  • run-pickup-stall · promiseAllWorkflow (python) · at 21:31:39Z · abandoned wrun_01M154HQD679KHJPRXT3DSV034
  • run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 21:31:39Z · abandoned wrun_01M154HQD5H9VKYZ9NX4GD1YD3
  • run-pickup-stall · parallelSleepWorkflow (python) · at 21:31:39Z · abandoned wrun_01M154HQDDRQA0F7JEFXN69R9A
  • run-pickup-stall · sleepingWorkflow (python) · at 21:31:39Z · abandoned wrun_01M154HQDBV34D5N1F2WQV196B
  • run-pickup-stall · nullByteWorkflow (python) · at 21:31:39Z · abandoned wrun_01M154HQDF9Y9WPNAHM0YSWN15
  • run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 21:32:19Z · abandoned wrun_41M154HCJZ0GRV958CPTMTQR6X
  • run-pickup-stall · deploymentId: 'latest' is a no-op in non-Vercel worlds (python) · at 21:32:39Z · abandoned wrun_01M154KJ0WPZXVKRM3FVRN04BP
  • run-pickup-stall · promiseAllWorkflow (python) · at 21:32:39Z · abandoned wrun_01M154KJ0XNMKG37Y0MDFZFX5D
  • run-pickup-stall · sleepingWorkflow (python) · at 21:32:39Z · abandoned wrun_01M154KJ12G1DAKAKP80REC3BB
  • run-pickup-stall · parallelSleepWorkflow (python) · at 21:32:39Z · abandoned wrun_01M154KJ1565S1XWF42EDPTRGC
  • run-pickup-stall · nullByteWorkflow (python) · at 21:32:39Z · abandoned wrun_01M154KJ18B7B8RSC1FYSVCAHN
  • run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 21:33:39Z · abandoned wrun_01M154NCMRFBWN8AXZ2WBKFPGJ
  • run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 21:33:39Z · abandoned wrun_01M154NCMNH57W89DK3C9HFTMN
  • run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 21:33:39Z · abandoned wrun_01M154NCN5XPFNW8WSYT928HQN
  • run-pickup-stall · cancelRun via CLI - cancelling a running workflow (python) · at 21:34:09Z · abandoned wrun_01M154PA0K7166QBBV03RTPK96
  • run-pickup-stall · cancelRun - cancelling a running workflow (python) · at 21:34:09Z · abandoned wrun_01M154PA0NY49F7FX0ZQS9SXTC
  • run-pickup-stall · sleepInLoopWorkflow - sleep inside loop with steps actually delays each iteration (python) · at 21:34:39Z · abandoned wrun_01M154Q789GMP8EKHWRVRJNTV6
  • run-pickup-stall · StepNotRegisteredError fails the step but workflow can catch it (nextjs-webpack) · at 21:34:41Z · abandoned wrun_01M154Q92HJ33QHHSGR1KBTWBH
  • run-pickup-stall · hookCleanupTestWorkflow - hook token reuse after workflow completion (nextjs-webpack) · at 21:34:58Z · abandoned wrun_01M154QT1KAQFJXGMT61DJCPPV

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

@NathanColosimo NathanColosimo mentioned this pull request Aug 25, 2026
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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

@NathanColosimo
NathanColosimo force-pushed the codex/replay-compile-overlap branch from 7a3a214 to ad97d27 Compare August 25, 2026 23:40
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The latest updates on your projects. Learn more about Vercel for GitHub.

Project Deployment Actions Updated (UTC)
example-nextjs-workflow-turbopack Ready Ready Preview, v0 Aug 28, 2026 9:28pm
example-nextjs-workflow-webpack Ready Ready Preview, v0 Aug 28, 2026 9:28pm
example-workflow Ready Ready Preview, v0 Aug 28, 2026 9:28pm
workbench-astro-workflow Ready Ready Preview, v0 Aug 28, 2026 9:28pm
workbench-express-workflow Ready Ready Preview, v0 Aug 28, 2026 9:28pm
workbench-fastify-workflow Ready Ready Preview, v0 Aug 28, 2026 9:28pm
workbench-hono-workflow Ready Ready Preview, v0 Aug 28, 2026 9:28pm
workbench-nestjs-workflow Ready Ready Preview, v0 Aug 28, 2026 9:28pm
workbench-nitro-workflow Ready Ready Preview, v0 Aug 28, 2026 9:28pm
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workbench-python-workflow Ready Ready Preview, v0 Aug 28, 2026 9:28pm
workbench-sveltekit-workflow Ready Ready Preview, v0 Aug 28, 2026 9:28pm
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workflow-tarballs Ready Ready Preview, v0 Aug 28, 2026 9:28pm
workflow-web Ready Ready Preview, v0 Aug 28, 2026 9:28pm

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📊 Workflow Benchmarks

commit d1ab139 · Fri, 28 Aug 2026 21:50:21 GMT · run logs

Backend: vercel · app: nextjs-turbopack

Metric Scenario Best (ms) P75 (ms) P90 (ms) P99 (ms) Samples
TTFS step 207 (-70%) 💚 1259 🔴 (+11%) 1346 🔴 (+18%) 🔻 1429 🔴 (+24%) 🔻 30
TTFS stream 195 (-15%) 1372 🔴 (+27%) 🔻 1416 🔴 (+28%) 🔻 1537 🔴 (+32%) 🔻 30
TTFS hook + stream 1361 (+178%) 🔻 1647 🔴 (+22%) 🔻 1697 🔴 (+23%) 🔻 1790 🔴 (+23%) 🔻 30
Fan-out TTFS Promise.all(100 steps) 579 (+2.8%) 2135 (+25%) 🔻 2191 (+21%) 🔻 2197 (+12%) 10
Fan-out TTLS Promise.all(100 steps) 1634 (-26%) 💚 3410 (-8.1%) 4129 (+9.7%) 4958 (-37%) 💚 10
STSO 1020 steps (inline) 101 (-11%) 153 (+9.3%) 174 (+8.1%) 674 (+242%) 🔻 1019
WO 1020 steps 160203 (+14%) 160203 (+14%) 160203 (+14%) 160203 (+14%) 1
CRTT first chunk (pooled) 102 (-11%) 157 (-33%) 💚 226 (-56%) 💚 790 (+19%) 🔻 28

Streams

Scenario CRTT 1st p75 p90 p99 CDV max iters
paced control (100/s, 60B) 125 (-13%) 141 (-72%) 236 (-66%) 636 (-35%) 108 (-76%) 10
size sweep (100/s, 160B-12KB) 147 (-18%) 158 (-32%) 235 (-58%) 523 (-42%) 152 (-36%) 10
replay gateway-gpt-5.4-nano-2000t (1x) 145 (-26%) 142 (-39%) 194 (-56%) 694 (-29%) 267 (-63%) 3
replay eve-gpt-5.6-sol-2000t (1x) 113 (-71%) 140 (-75%) 191 (-89%) 457 (-89%) 473 (-78%) 2
replay eve-gpt-5.6-sol-2000t (2x) 142 (-10%) 274 (-63%) 452 (-57%) 910 (-31%) 346 (-39%) 3
📈 STSO distribution vs main (inline / queue-hop histograms)

1020 steps (inline)

Cumulative STSO time: main 139837ms → this run 158916ms (Δ +19079ms, +14%)

  100-150 ms  ███████████████████┃████  main 857  this 729  -128
  150-200 ms  ████░┃                    main 152  this 229   +77
  200-250 ms  ┃                         main   8  this  27   +19
  250-300 ms  ┃                         main   0  this  10   +10
  300-350 ms  ┃                         main   2  this   5    +3
  350-400 ms  ┃                         main   0  this   2    +2
  400-450 ms  ┃                         main   0  this   1    +1
  450-500 ms  ┃                         main   0  this   2    +2
  500-550 ms  ┃                         main   0  this   1    +1
  600-650 ms  ┃                         main   0  this   1    +1
  650-700 ms  ┃                         main   0  this   3    +3
  700-750 ms  ┃                         main   0  this   2    +2
  750-800 ms  ┃                         main   0  this   1    +1
  800-850 ms  ┃                         main   0  this   1    +1
  850-900 ms  ┃                         main   0  this   1    +1
  900-950 ms  ┃                         main   0  this   1    +1
 950-1000 ms  ┃                         main   0  this   1    +1
1000-1050 ms  ┃                         main   0  this   1    +1
1150-1200 ms  ┃                         main   0  this   1    +1
📈 CRTT drill-down vs main (RTT distributions & profiles) 
variant  RTT 1ms→5s+             avg         p50         p90         p99     n
control  ······▅█▁▁···  126.1 (-55%)  110 (-43%)  236 (-66%)  636 (-35%)  3000
sweep    ······▄█▂▁···  133.7 (-36%)  114 (-34%)  235 (-58%)  523 (-42%)  3000
gw 1x    ·····▁▅█▁▁···  128.5 (-37%)  114 (-30%)  194 (-56%)  694 (-29%)  5295
eve 1x   ·····▁▆█▂▁···  124.4 (-71%)  110 (-40%)  191 (-89%)  457 (-89%)  5186
eve 2x   ·····▁▂█▃▁▁··  181.5 (-53%)  140 (-43%)  452 (-57%)  910 (-31%)  7779

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

control  ▄▃▃▅▄▃▁▆█▄  104–153ms
sweep    █▃▆▃▁▂▂▂▁▂  117–174ms
gw 1x    █▁▂▄▁▂▁▁▁▁  110–207ms
eve 1x   ▄█▅▃▆▄▅▇▇▁  100–145ms
eve 2x   ▂▁▂▁▁▂▃█▄▆  128–303ms

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

sweep  ██▄▁▄▁▄  131–137ms

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

control  ▁▅▅▅▄█▃▇▆▄  30–47ms
sweep    ▁▄█▇▅▆█▅▆█  35–59ms
gw 1x    █▃▁▄▄▃▃▃▂▃  32–45ms
eve 1x   ▃█▂▁▇▅▆▂▄▂  22–30ms
eve 2x   ▅▃▃▁▅▂▃▇▄█  23–37ms
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.

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Framework Flow route Step reg. Framework output
hono 200.9 KiB (±0) 40.4 KiB (±0) 1.76 MiB (+1.7 KiB)
nextjs-turbopack 206.3 KiB (±0) 439 B (±0) 765.0 KiB (+1.1 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.

d1ab139 · run

@NathanColosimo
NathanColosimo marked this pull request as ready for review August 26, 2026 04:41
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NathanColosimo requested a review from a team as a code owner August 26, 2026 04:41
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NathanColosimo force-pushed the codex/replay-compile-overlap branch from 954f0b3 to 0e41f67 Compare August 26, 2026 20:51
@NathanColosimo
Overlap workflow compile with replay loading
1871577 
Signed-off-by: Nathan Colosimo <110621881+NathanColosimo@users.noreply.github.com>
@NathanColosimo
Fix replay compilation scheduling
d1ab139
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