🎯 Changes

This PR fixes a stale cleanup callback issue in adapter hooks that support onUnmount.

Before this change, these hooks registered an unmount cleanup with an empty dependency array and read mergedOptions.onUnmount directly inside that cleanup. That meant the cleanup closed over the value from the first render. If a consumer re-rendered with a new onUnmount callback, the hook could still call the old callback during unmount.

This change keeps the existing "register cleanup once" behavior, but makes the cleanup read the latest onUnmount callback instead of the initial one.

Updated hooks:

• packages/react-pacer/src/debouncer/useDebouncer.ts
• packages/react-pacer/src/async-debouncer/useAsyncDebouncer.ts
• packages/react-pacer/src/rate-limiter/useRateLimiter.ts
• packages/preact-pacer/src/debouncer/useDebouncer.ts

Why this approach

I wanted to keep this fix as small and low-risk as possible.

I considered whether the previous behavior might have been intentional, since the cleanup effect is deliberately registered with [] to keep teardown stable. However, the rest of these hooks already update runtime behavior from the latest render by reassigning fn and calling setOptions(mergedOptions) on each render. Given that, treating onUnmount as "initial render only" felt inconsistent with the rest of the hook contract and with how consumers would naturally expect a cleanup option to behave.

Because of that, I treated this as a stale-closure bug rather than an intentional "initial-only" API.

What changed in the implementation

The change is intentionally minimal:

• keep the existing empty-deps cleanup effect
• keep the existing default cleanup behavior
• avoid introducing a new custom hook such as useLatest
• avoid changing the public API
• store only the latest onUnmount callback in a ref
• read ref.current inside the unmount cleanup

So the behavior changes only in one place:

• previously: cleanup used the first-render onUnmount
• now: cleanup uses the latest onUnmount

Motivation

This matters when onUnmount depends on props or render-time values and changes over the component lifecycle. In that case, the old behavior could execute outdated cleanup logic during unmount.

This PR fixes that without changing how often the effect is registered or how the default teardown works.

Local validation

• pnpm run test:pr --base=53fb52ec --head=HEAD
  • Successfully ran targets test:eslint, test:sherif, test:knip, test:docs, test:lib, test:types, build for 86 projects and 4 tasks they depend on
• pnpm run test:ci
  • Successfully ran targets test:eslint, test:sherif, test:knip, test:docs, test:lib, test:types, build for 169 projects (3m)
• pnpm changeset status --since=53fb52ec --verbose
  • confirmed patch releases for @tanstack/react-pacer and @tanstack/preact-pacer

✅ Checklist

• I have followed the steps in the Contributing guide.
• I have tested this code locally with pnpm run test:pr.

🚀 Release Impact

• This change affects published code, and I have generated a changeset.
• This change is docs/CI/dev-only (no release).

Summary by CodeRabbit

Release Notes

• Bug Fixes
  • Fixed unmount cleanup callback handling to use the most recent callback provided, ensuring proper teardown behavior when component options change during the component lifecycle.