fix: reset pending state after leading-only debouncer execution

[Don-Erfan]

With leading: true and trailing: true, a single call to maybeExecute executed on the leading edge but still set isPending: true and stored lastArgs. The trailing timeout correctly skips calls already handled by the leading edge, so nothing ever reset that state: status stayed 'pending' forever and a later flush() re-executed the function with stale, already-executed arguments.

Only set isPending/lastArgs for calls not consumed by the leading edge. Apply the same fix to LiteDebouncer, which stored lastArgs unconditionally and could re-execute a leading-edge call via flush().

🎯 Changes

✅ 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

  • Fixed debounced actions configured for leading and trailing execution being invoked twice with the same arguments.
  • Improved flush() behavior so it no longer re-executes an already completed leading-edge call.
  • Corrected pending-state and idle-status handling after a single debounced execution.

• Tests

  • Added coverage for leading/trailing execution, flush(), pending state, and idle transitions.

[coderabbitai]

📝 Walkthrough

Walkthrough

Updated both debouncer implementations so leading-edge calls are not re-executed by trailing execution or flush(). Added tests covering duplicate prevention, cleared arguments, pending state, and idle status.

Changes

Debouncer leading-edge behavior

Layer / File(s)	Summary
Prevent duplicate trailing and flush execution packages/pacer/src/debouncer.ts, packages/pacer-lite/src/lite-debouncer.ts, packages/pacer/tests/debouncer.test.ts, packages/pacer-lite/tests/lite-debouncer.test.ts	Leading-handled calls no longer retain arguments or enter pending trailing state. Tests verify that flush() does not invoke them again and that the debouncer clears arguments and returns to idle.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly summarizes the main debouncer behavior fix.
Description check	✅ Passed	The description covers the bug, fix, checklist, and release impact, though the Changes section is mostly placeholder text.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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