feat(preview-server): buffer console logs until spinner is done

[gabrielmfern]

I've always been annoyed at the fact that ora's spinners conflict with console.log statements during rendering, which sometimes, ends up eating away what you wanted to see in a console.log statement. To fix this, I've tried using process.stdout.cork and uncork, but console.err and console.warn write to process.stderr which is where ora also writes to, and corking will also buffer the spinner itself, which we don't want.

So, this just replaces the global console functions, storing the arguments to pass to the log function, and then once the spinner is done sends it all into the original function.

Before	After
2025-12-12.18-06-45.mp4	2025-12-12.18-04-47.mp4

---

Summary by cubic

Prevents spinner output from overwriting console logs in the preview server by buffering logs during rendering and flushing them after the spinner stops.

• New Features

  • Queue console.log/info/warn/error while the ora spinner runs, then flush and restore originals on success or error.
  • Send spinner output to stderr explicitly to avoid conflicts and ensure clean log output.

• Bug Fixes

  • Handle nested buffer/flush calls to prevent race conditions and only flush once all buffers are released.

^{Written for commit 9520b08. Summary will update automatically on new commits.}

[changeset-bot]

🦋 Changeset detected

Latest commit: 9520b08

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

This PR includes changesets to release 2 packages

Name	Type
@react-email/preview-server	Patch
react-email	Patch

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[vercel]

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Project	Deployment	Review	Updated (UTC)
react-email	Ready	Preview, Comment	Dec 12, 2025 9:07pm
react-email-demo	Ready	Preview, Comment	Dec 12, 2025 9:07pm

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/resend/react-email/@react-email/preview-server@2725

commit: 9520b08

[cubic-dev-ai]

1 issue found across 2 files

Prompt for AI agents (all 1 issues)

Check if these issues are valid — if so, understand the root cause of each and fix them.


<file name="packages/preview-server/src/actions/render-email-by-path.tsx">

<violation number="1" location="packages/preview-server/src/actions/render-email-by-path.tsx:76">
P1: Race condition: concurrent calls to `renderEmailByPath` can corrupt global console methods. When a second call starts before the first finishes, it captures the buffered function as `original` instead of the real console method. Consider storing the original console methods once at module scope, or using a reference counter to only restore when all concurrent calls complete.</violation>
</file>

_{Reply to cubic to teach it or ask questions. Re-run a review with @cubic-dev-ai review this PR}