test(replay): comprehensive replay engine tests

[sepehr-safari]

Summary

Adds comprehensive test coverage for the replay engine (packages/toolkit/src/replay/engine.ts), addressing GitHub Issue #61.

What's Tested

55 tests across 9 describe blocks covering all public API surface:

• Construction — new ReplayEngine(events, failures, options), immutability of input arrays
• totalEvents getter — correct count for normal, empty, and single-event cases
• current getter — starts at 0, returns -1 for empty, advances after step(), reflects startIndex
• step() — returns first/next event, returns null when complete, includes empty failures array, returns {event, failures, index}
• stepBack() — returns null at start and after single step, goes back one event
• jumpTo(index) — jumps to valid index, returns null for negative/out-of-range/empty
• getState() — returns played/remaining/complete snapshot, includes failures in played events, handles empty
• reset() — returns to index 0, allows re-stepping, handles empty
• Failures filtering — only failures matching current event's id returned via step() and in getState().played
• Edge cases — empty events array, single event, options.startIndex (at start, mid, last, default)

Test Pattern

Uses the same makeEvent helper pattern as packages/toolkit/src/core/detection.test.ts, with a local makeFailure helper for building Failure objects. Imports from ./engine.js as specified.

Checklist

• pnpm test — 280 tests pass (55 new)
• pnpm lint — clean
• pnpm typecheck — clean
• pnpm format — clean

Closes #61

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Project	Deployment	Actions	Updated (UTC)
ocpp-debugkit-web	Ready	Preview, Comment	Jul 8, 2026 5:45pm