fix(rivetkit): add back dev hot reloading in next

[NathanFlurry]

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[NathanFlurry]

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This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
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• fix(rivetkit/next-js): fix request handler #4001
• fix(rivetkit): handle undefined options with scheduling #4000
• chore(engine): add force shutdown timeout #3999
• fix(rivetkit): fix fetch handler in nextjs serverless #3998
• fix(rivetkit): add back dev hot reloading in next #3997 👈 (View in Graphite)
• fix(rivetkit): fix routing of /websocket #3995
• fix(rivetkit): add config parameters to spawned serverless engine for local dev #3994
• main

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[claude]

PR Review: fix(rivetkit): add back dev hot reloading in next

Summary

This PR reverts a temporary debugging change that disabled the development hot reloading feature in the Next.js integration. The change restores the proper environment check for file watching.

Changes

File: rivetkit-typescript/packages/next-js/src/mod.ts:55

• Before: if (false) - Hot reloading was disabled
• After: if (process.env.NODE_ENV === "development") - Hot reloading enabled in development

Review

✅ Code Quality

• The change is minimal and focused
• Restores the intended behavior for development environments
• The condition properly checks NODE_ENV which is the standard Next.js environment variable
• Code follows existing patterns in the file (line 14 uses the same check for similar environment-based logic)

✅ Best Practices

• Appropriate use of environment-based conditional logic
• The file watching mechanism is well-documented with comments explaining the hack and why it's necessary (lines 147-154)
• The implementation properly handles cleanup with abort controllers and interval clearing
• Follows the codebase pattern of using environment checks for development-specific behavior

✅ Functionality

• Re-enables the handleRequestWithFileWatcher function which:
  • Watches for file changes in the compiled Next.js route (.next/server/app/api/rivet/[...all]/route.js)
  • Aborts long-running requests when files change to prevent stale actors from running old code
  • Properly cleans up file watchers when streams finish or requests are aborted
• This is necessary because Next.js doesn't terminate long-running requests on file changes, which would leave stale Rivet Actors running with old code during development
• The file watcher correctly handles:
  • SSE streams (waits for stream completion)
  • Non-streaming responses (cleans up immediately)
  • Request aborts (cleans up listeners and intervals)

🔍 Observations

1. Test Coverage: No tests found in this package - the hot reloading logic could benefit from integration tests to prevent accidental disabling in the future
2. Polling Implementation: The file watcher uses polling (every 1000ms at line 191) rather than native file system events, which is documented as intentional to avoid cross-platform issues and inotify limit problems
3. Hardcoded Path: The route path is hardcoded to .next/server/app/api/rivet/[...all]/route.js (line 160-162), which assumes a specific routing structure - this is acceptable for a framework integration but worth noting

✅ Security & Performance

• Security: No security concerns introduced. The feature is properly scoped to development only
• Performance:
  • Performance impact is limited to development environment only (production unaffected)
  • The polling interval (1s) is reasonable for development use and won't cause excessive CPU usage
  • Cleanup is properly handled to prevent memory leaks from abandoned intervals

📝 Minor Suggestions

While the PR is fine as-is, consider for future improvements:

1. Add integration tests that verify the file watching behavior
2. Consider adding a comment explaining why if (false) was temporarily used (if this was debugging code that accidentally got committed)

Verdict

LGTM ✅

This is a clean fix that restores important development experience functionality. The change is:

• Safe and well-scoped
• Properly conditioned to only affect development environments
• Necessary for maintaining a good developer experience with Next.js hot reloading
• Consistent with the codebase patterns

The implementation is well-thought-out with proper cleanup, error handling, and documentation. Approving for merge.

[pkg-pr-new]

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commit: 6e92446

[graphite-app]

Merge activity

• Jan 22, 6:58 AM UTC: NathanFlurry added this pull request to the Graphite merge queue.
• Jan 22, 6:59 AM UTC: CI is running for this pull request on a draft pull request (#4007) due to your merge queue CI optimization settings.
• Jan 22, 7:00 AM UTC: Merged by the Graphite merge queue via draft PR: #4007.