fix(core): prevent incorrect transition state when transitionDuration is 0

[ENvironmentSet]

Closes FECO-90

Summary

• transitionDuration: 0 설정 시 간헐적으로 transition state가 enter-done 대신 enter-active로 잘못 설정되는 이슈를 수정합니다.
• dispatchEvent에서 aggregate() 호출 시 Math.max(newEvent.eventDate, Date.now())를 사용하여 now >= eventDate를 보장합니다.

Root Cause

core/src/utils/time.ts의 time() 함수는 이벤트 정렬을 위해 같은 밀리초 내 중복 호출 시 sub-millisecond 오프셋을 추가합니다 (e.g., 1000000.001). dispatchEvent에서 aggregate(events, Date.now())를 호출할 때, Date.now()가 같은 밀리초를 반환하면 now < eventDate가 되어 now - eventDate >= transitionDuration(0) 판정이 실패합니다.

이로 인해 activity가 enter-done 대신 enter-active 상태로 진입하게 됩니다.

Test plan

• yarn workspace @stackflow/core test — 84개 테스트 모두 통과
• Demo 앱에서 transitionDuration: 0으로 반복 네비게이션 시 정상 동작 확인
• Demo 앱에서 transitionDuration: 270 (기본값)으로 전환 애니메이션 정상 작동 확인

🤖 Generated with Claude Code

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🦋 Changeset detected

Latest commit: da242aa

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

This PR includes changesets to release 1 package

Name	Type
@stackflow/core	Patch

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• .changeset/fix-transition-duration-zero-jitter.md
• core/src/makeCoreStore.ts

---

📝 Walkthrough

Summary by CodeRabbit

• Bug Fixes
  • Fixed intermittent incorrect transition state when transition duration is set to zero.

Walkthrough

This PR fixes an intermittent state aggregation bug in @stackflow/core when transitionDuration is 0. The fix modifies dispatchEvent to pass the maximum of the event's date and current time to the aggregate function, ensuring correct timing during initial state calculation.

Changes

Cohort / File(s)	Summary
Changelog Entry .changeset/fix-transition-duration-zero-jitter.md	Adds patch release note documenting the fix for incorrect transition state when transitionDuration is 0.
Core Logic core/src/makeCoreStore.ts	Updates dispatchEvent to pass Math.max(newEvent.eventDate, Date.now()) to aggregate instead of just Date.now(), ensuring the timestamp is at least the new event's date.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main fix: preventing incorrect transition state when transitionDuration is 0, which directly aligns with the primary change in the changeset.
Description check	✅ Passed	The description provides detailed context about the fix, including root cause analysis, the specific problem, and the solution, all of which directly relate to the changes in the pull request.

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• Commit unit tests in branch fix/transition-duration-zero-jitter

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