fix(rivetkit): fix fetch handler in nextjs serverless

[NathanFlurry]

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[NathanFlurry]

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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 👈 (View in Graphite)
• fix(rivetkit): add back dev hot reloading in next #3997
• 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 fetch handler in Next.js serverless

Summary

This PR fixes a critical bug in the Next.js integration where the global fetch function was incorrectly passed to handleRequestWithFileWatcher instead of registry.handler. This would cause requests in development mode to bypass the RivetKit handler entirely.

Code Quality ✅

The fix is correct and appropriate:

• Line 57 now correctly passes registry.handler instead of the global fetch function
• This aligns with the production code path (line 61) which also uses registry.handler
• The handleRequestWithFileWatcher function signature at line 84 accepts a generic fetch-compatible handler, so this change is type-safe

Bug Analysis 🐛

The bug:

• In development mode, handleRequestWithFileWatcher was being passed the global fetch function
• This would have caused requests to be handled by the browser/Node.js fetch API instead of RivetKit handler
• The request would fail because the global fetch expects an absolute URL, not the RivetKit routing logic

Impact: This would break all development mode requests in Next.js serverless deployments.

Code Consistency ✅

The fix maintains consistency with the production code path. Both paths now correctly use registry.handler, which ensures the runtime is initialized, starts the serverless handler, and routes requests through RivetKit request handling logic.

Testing Recommendations 🧪

While this is a simple one-line fix, consider:

1. Manual testing in Next.js development mode to verify requests are handled correctly
2. Verifying that file watching still works as expected
3. Testing with long-running SSE streams to ensure the abort signal handling works properly

Performance ✅

No performance concerns. The change simply routes to the correct handler.

Security ✅

No security concerns. This fixes a bug that would have prevented proper request handling.

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Overall Assessment: ✅ LGTM - This is a straightforward bug fix that corrects an obvious error. The change is minimal, correct, and maintains consistency with the production code path.

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commit: 45f73be

[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.