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The Wire ยท Showcase

NEXT.JS TEST CACHING LANDS, APP SHELLS PLUMBING SHIPS

By RepoJournal ยท Filed ยท About Vercel

Next.js cut test reruns by memoizing passing tests across workflow attempts, while experimental App Shell support starts wiring up the client-side prefetch pipeline.

The action cache for passing tests [1] is live in next.js, which means re-triggered CI runs skip tests that already passed on the first attempt. Sync writes to a flat file track the winners, so timeouts or cancellations don't waste compute on redundant passes. In parallel, the experimental.appShells feature flag [2] landed as pure plumbing: config field, zod schema, and `process.env.__NEXT_APP_SHELLS` define are in place, but nothing reads it yet. Subsequent PRs will wire the server and client behavior behind it. Both the Cache Components prerender semantics [3] and the corresponding test coverage [4] shipped to lock in fallback boundary behavior when `notFound()`, `forbidden()`, and `unauthorized()` recovery routes through Cache Components. The devlow-bench runner [5] now reports p50/p90/p99 percentiles instead of means, with Mann-Whitney p-values for cleaner signal, plus per-attempt buffering to isolate flaky page-load runs from the final stats. Across the AI desk, Vercel's SDK locked in serviceTier reads from both the Gemini response header [6] and the usageMetadata body [7], so streaming and non-streaming calls both surface the applied tier. CLI got a `--project` flag [8] for all major commands (build, deploy, pull, dev), enabling non-interactive CI and agent-driven workflows without prompts. Python functions now support runtime cache configuration [9], and blob commands speak OIDC [10] alongside the legacy token path. Workflow repo fixed trace viewer zoom clipping [12], reports corrupted event logs as a distinct error code [11], and forward-ported a stale wait replay race fix [13]. SDK bumped to 1.21.6 [14] with vcrRepository permission fields added to microfrontends and projects APIs.

Action items

References

  1. [1] use the action cache for passing tests (#93954) vercel/next.js
  2. [2] Add experimental.appShells feature flag (#93997) vercel/next.js
  3. [3] Prerender HTTP access fallbacks with Cache Components semantics โ†— vercel/next.js
  4. [4] [test] Prerendering HTTP access fallback pages with Cache Components โ†— vercel/next.js
  5. [5] devlow-bench: percentile-based comparison and run retries โ†— vercel/next.js
  6. [6] fix(google): read serviceTier from x-gemini-service-tier response header (#14937) vercel/ai
  7. [7] fix(google): read serviceTier from usageMetadata in stream + generate (#15488) vercel/ai
  8. [8] [cli] Add `--project` flag to `build`, `deploy`, `pull`, and `dev` โ†— vercel/vercel
  9. [9] [python] configure runtime cache for Python functions โ†— vercel/vercel
  10. [10] [cli] Support OIDC auth for blob commands โ†— vercel/vercel
  11. [11] Report corrupted event logs distinctly โ†— vercel/workflow
  12. [12] trace viewer bug fix + file cleanup โ†— vercel/workflow
  13. [13] [codex] Forward port stale wait replay fix โ†— vercel/workflow
  14. [14] chore: ๐Ÿ Update SDK - Generate VERCEL 1.21.6 โ†— vercel/sdk

FAQ

What changed in Vercel on May 21, 2026?
Next.js cut test reruns by memoizing passing tests across workflow attempts, while experimental App Shell support starts wiring up the client-side prefetch pipeline.
What should Vercel teams do about it?
Test and merge Next.js test caching into your CI, then redeploy workflow to see reruns skip โ€ข Upgrade @vercel/blob to use OIDC auth if you're already running `vercel env pull` โ€ข Update SDK to 1.21.6 if you consume vcrRepository permission fields
Which Vercel repositories shipped on May 21, 2026?
vercel/next.js, vercel/ai, vercel/vercel, vercel/workflow, vercel/sdk

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