Update: Optimize buildSteps for large event counts

[FL4TLiN3]

Summary

• Implement incremental updates for buildSteps in useStepStore
• Cache stepMap and processedCount in useRef to avoid full rebuilds on every event
• Only rebuild when events are truncated (MAX_EVENTS=1000) or historical events are loaded

Closes #42

Test plan

• pnpm typecheck passes
• pnpm test passes
• pnpm format-and-lint passes
• pnpm check-deps passes
• pnpm build passes
• E2E tests for long-running sessions with 500+ events

---

Note

Incremental, cached step map processing in useStepStore, rebuilding only on truncation or historical event loads.

• tui/hooks (packages/tui/src/hooks/state/use-step-store.ts):
  • Implement incremental processing using cached stepMapRef, processedCountRef, and needsRebuildRef with a useEffect update loop.
  • Add helpers: getOrCreateStep, processEvent, buildStepsFromMap; clone tool entries when building steps.
  • Handle MAX_EVENTS truncation and setHistoricalEvents by marking rebuild; compute completedSteps/currentStep without useMemo.
• Changeset: add patch note for @perstack/tui describing the optimization.

^{Written by Cursor Bugbot for commit b7b5782. This will update automatically on new commits. Configure here.}

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Codecov Report

✅ All modified and coverable lines are covered by tests.

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