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feat(ci): warm Next.js builds via Turbopack persistent cache on a sticky disk#5869

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waleedlatif1 merged 2 commits into
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Jul 23, 2026
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feat(ci): warm Next.js builds via Turbopack persistent cache on a sticky disk#5869
waleedlatif1 merged 2 commits into
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ci/turbopack-warm-build

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@waleedlatif1 waleedlatif1 commented Jul 22, 2026

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Summary

  • Enable Next 16's Turbopack persistent build cache (experimental.turbopackFileSystemCacheForBuild, beta) behind a NEXT_TURBOPACK_BUILD_CACHE env gate — only the CI check build opts in; production image builds keep the default cold path until the feature stabilizes
  • Mount ./apps/sim/.next/cache as a Blacksmith sticky disk via the existing cache-mount action (same event/fork namespacing as the other mounts) — the Turbopack cache is ~5 GB, which sticky disks mount in ~1s while an actions/cache round-trip would eat the warm-build win; the GitHub-fallback path inside cache-mount still works
  • Measured locally on this repo: 105s cold compile → 22s warm (4.8×). The Build App check is the merge gate (~3m40s, compile is ~80% of it), so this is direct merge-wait reduction; expect the effect from the second run onward as the disk warms
  • Follow-up to fix(ci): save the Next.js build cache every run instead of freezing it at the lockfile key #5859 (which fixed the frozen actions/cache keying but revealed the cache carried almost nothing without the Turbopack flag)

Type of Change

  • Improvement

Testing

Local A/B: cold build 105s (cache written, 4.8 GB), immediate rebuild 22.1s, byte-identical route table. This PR's own Build App run is cold (first sticky-disk fill); subsequent runs on the branch/staging show the warm number.

Checklist

  • Code follows project style guidelines
  • Self-reviewed my changes
  • Tests added/updated and passing
  • No new warnings introduced
  • I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

@waleedlatif1
feat(ci): warm Next.js builds via Turbopack persistent cache on a sti…
5d7c11c 
…cky disk

- enable experimental.turbopackFileSystemCacheForBuild behind
  NEXT_TURBOPACK_BUILD_CACHE so only the CI check build opts in; production
  image builds stay on the default cold path until the feature stabilizes
- mount ./apps/sim/.next/cache as a Blacksmith sticky disk (cache-mount)
  instead of actions/cache: the turbopack cache is ~5 GB, which a sticky disk
  mounts in ~1s while an actions/cache round-trip would eat the win
- measured locally: 105s cold compile vs 22s warm (4.8x)
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docs Ready Ready Preview, Comment Jul 23, 2026 12:08am

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@cursor

cursor Bot commented Jul 22, 2026 •
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PR Summary

Low Risk
CI and opt-in Next experimental build caching only; production builds are unchanged and there is no auth or data-path impact.

Overview
Speeds up the Build App merge gate by turning on Turbopack’s persistent build cache for that CI job only, and persisting the large .next/cache output on a sticky disk instead of actions/cache.

The Build App workflow now mounts ./apps/sim/.next/cache through the same cache-mount action as other caches (event/fork namespacing unchanged), replacing the per-run actions/cache restore that was costly for a ~5 GB Turbopack cache. The build step sets NEXT_TURBOPACK_BUILD_CACHE=1, which gates experimental.turbopackFileSystemCacheForBuild in next.config.ts. Production/image builds keep the default cold path because they do not set that env var.

Reviewed by Cursor Bugbot for commit 4790a49. Configure here.

@greptile-apps

greptile-apps Bot commented Jul 22, 2026 •
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Greptile Summary

This PR speeds up CI builds with Next.js Turbopack’s persistent filesystem cache. The main changes are:

  • Mount the Next.js build cache on the existing provider-aware sticky disk.
  • Enable the persistent Turbopack cache only for the CI build check.
  • Keep production image builds on the default cold-build path.

Confidence Score: 5/5

This looks safe to merge.

  • No blocking issues found in the changed code.

Important Files Changed

Filename Overview
.github/workflows/test-build.yml Moves the Next.js build cache to the shared cache-mount action and opts the CI build into persistent Turbopack caching.
apps/sim/next.config.ts Adds an environment-controlled switch for Turbopack’s persistent build cache.

Reviews (2): Last reviewed commit: "chore(ci): drop the superseded actions/c..." | Re-trigger Greptile

greptile-apps[bot]
greptile-apps Bot reviewed Jul 22, 2026
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Comment thread .github/workflows/test-build.yml
@waleedlatif1

waleedlatif1 commented Jul 23, 2026

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waleedlatif1 commented Jul 23, 2026

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✅ Bugbot reviewed your changes and found no new issues!

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Reviewed by Cursor Bugbot for commit 4790a49. Configure here.

@waleedlatif1
waleedlatif1 merged commit 02bc8f1 into staging Jul 23, 2026
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@waleedlatif1
waleedlatif1 deleted the ci/turbopack-warm-build branch July 23, 2026 00:11
@waleedlatif1 waleedlatif1 mentioned this pull request Jul 23, 2026
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