fix(pacer): lastResult should reflect resolved value

[gwansikk]

🎯 Changes

lastResult in AsyncDebouncerState, AsyncThrottlerState, and AsyncRateLimiterState is typed as ReturnType<TFn> | undefined, which resolves to Promise<T> | undefined since TFn extends AnyAsyncFunction. At runtime, the stored value is always the awaited result.

- lastResult: ReturnType<TFn> | undefined
+ lastResult: Awaited<ReturnType<TFn>> | undefined

✅ 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

• Bug Fixes
  • Corrected async utilities' lastResult property to store the actual resolved value from async function executions instead of promise types.

[coderabbitai]

📝 Walkthrough

Walkthrough

Updates the lastResult type across three async utility classes in the @tanstack/pacer package to store the resolved value (Awaited<ReturnType<TFn>>) instead of the raw return type, with a corresponding changeset entry documenting the patch-level bump.

Changes

Cohort / File(s)	Summary
Type Definition Clarification packages/pacer/src/async-debouncer.ts, packages/pacer/src/async-rate-limiter.ts, packages/pacer/src/async-throttler.ts	Updated lastResult property type from ReturnType<TFn> | undefined to Awaited<ReturnType<TFn>> | undefined across all three async state interfaces to correctly represent resolved values.
Changelog Entry .changeset/pretty-llamas-happen.md	Added changeset documenting patch-level bump for @tanstack/pacer with note that lastResult reflects the resolved value.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

A rabbit hops through types with glee, 🐰
Awaited values, now they're free!
No promises stored, just truth revealed,
The resolved results are now sealed.
Three utilities in harmony!

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change—correcting the type of lastResult to reflect the resolved value rather than the raw Promise type.
Description check	✅ Passed	The PR description covers all required sections: detailed explanation of changes with code diff, completed checklist items confirming contribution guide compliance and testing, and clear release impact statement with changeset added.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Caution

Some comments are outside the diff and can’t be posted inline due to platform limitations.

⚠️ Outside diff range comments (1)

packages/pacer/src/async-throttler.ts (1)

121-125: 🛠️ Refactor suggestion | 🟠 Major

Consider updating onSuccess callback type for consistency.

The onSuccess callback receives the awaited result at runtime (line 427), but its type signature still declares result: ReturnType<TFn>, which resolves to Promise<T>. This creates a type inconsistency that's currently hidden by the as ReturnType<TFn> cast at line 427.

For type correctness and consistency with the lastResult fix, consider updating the callback signature:

  onSuccess?: (
-   result: ReturnType<TFn>,
+   result: Awaited<ReturnType<TFn>>,
    args: Parameters<TFn>,
    asyncThrottler: AsyncThrottler<TFn>,
  ) => void

This same pattern appears in async-debouncer.ts and async-rate-limiter.ts.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@packages/pacer/src/async-throttler.ts` around lines 121 - 125, Update the
onSuccess callback type to accept the awaited result instead of the raw Promise
so the runtime value matches the type: change the signature of onSuccess on
AsyncThrottler<TFn> to use Awaited<ReturnType<TFn>> (or equivalent) for the
result parameter and adjust any related references like lastResult; apply the
same change pattern to the onSuccess definitions in async-debouncer.ts and
async-rate-limiter.ts to keep types consistent with the actual awaited value
passed at runtime (look for the onSuccess property and places where result is
cast as ReturnType<TFn>).

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Outside diff comments:
In `@packages/pacer/src/async-throttler.ts`:
- Around line 121-125: Update the onSuccess callback type to accept the awaited
result instead of the raw Promise so the runtime value matches the type: change
the signature of onSuccess on AsyncThrottler<TFn> to use
Awaited<ReturnType<TFn>> (or equivalent) for the result parameter and adjust any
related references like lastResult; apply the same change pattern to the
onSuccess definitions in async-debouncer.ts and async-rate-limiter.ts to keep
types consistent with the actual awaited value passed at runtime (look for the
onSuccess property and places where result is cast as ReturnType<TFn>).

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 4aa19ba5-9e8a-412f-850e-c321ae804e4b

📥 Commits

Reviewing files that changed from the base of the PR and between 05b7c4d and e8d0bcd.

📒 Files selected for processing (4)

• .changeset/pretty-llamas-happen.md
• packages/pacer/src/async-debouncer.ts
• packages/pacer/src/async-rate-limiter.ts
• packages/pacer/src/async-throttler.ts