fix(useThrottledCallback): invoke the callback when the first value is false

[bbjbc]

Overview

useThrottledCallback drops the very first call when the value is false.

The hook skips redundant invocations by comparing the incoming value against the last one it forwarded to onChange. That comparison is seeded with false:

const ref = useRef({ value: false, clearPreviousThrottle: () => {} });
...
if (nextValue === ref.current.value) {
  return;
}

Since the hook takes no initial value from the caller, a first call of false matches the seed and returns early, so onChange never fires.

const onChange = vi.fn();
const { result } = renderHookSSR(() => useThrottledCallback({ onChange, timeThreshold: 100 }));

result.current(false);
// onChange is never called

result.current(true);
// works. only the first `false` is lost

This matters for consumers whose state does not start at false. If a panel is open by default, the first close emits false, and that transition is silently dropped with no way to tell the hook the state started as true.

useDebouncedCallback has the same seed. I left it alone here because #267 is already changing that line. Its generic rewrite switches the seed to null, which fixes this case as a side effect, though a narrower version of the problem survives there: a first call of null would still be dropped.

Changes

• Seed the comparison with a module-level sentinel instead of false, so the first call is forwarded regardless of its value. The dedup comparison itself is unchanged, so repeated values are still skipped.
• Add two tests: one for the first false, one asserting a repeated false is still skipped so the dedup behavior stays pinned.

A Symbol is used rather than null or undefined because it cannot collide with a caller-supplied value if this hook later becomes generic, as useDebouncedCallback is doing in #267.

Existing tests all start with result.current(true), which is why this was not caught. The early-return branch is already covered by the repeated-true cases, so branch coverage was 100% while the first-call-false path was never exercised.

Checklist

• Did you write the test code?
• Have you run yarn run fix to format and lint the code and docs?
• Have you run yarn run test:coverage to make sure there is no uncovered line?
• Did you write the JSDoc?

[changeset-bot]

🦋 Changeset detected

Latest commit: 8f04f14

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
react-simplikit	Patch

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (ea7deae) to head (8f04f14).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #404   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           58        58           
  Lines         1639      1643    +4     
  Branches       499       499           
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+ Hits          1639      1643    +4     

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[hyesungoh]

Thanks for your contribution! 👍