[benrowe]

Summary

Adds timestamp tracking to GateEvaluation and ActionSkip value objects to improve observability and enable time-based analysis of workflow execution.

• ✅ Added float $timestamp property to GateEvaluation (readonly value object)
• ✅ Added float $timestamp property to ActionSkip (readonly value object)
• ✅ Auto-generates timestamp using microtime(true) (follows existing Event.php pattern)
• ✅ Supports explicit timestamp for deserialization (backward compatible)
• ✅ Updated TransitionContext serialization to persist timestamps
• ✅ Full backward compatibility - old serialized data loads without timestamps

Implementation Details

Pattern Used (following existing Event.php):

readonly class GateEvaluation
{
    public readonly float $timestamp;

    public function __construct(
        public Gate $gate,
        public GateResult $result,
        public bool $isActionGate,
        float $timestamp = 0.0,
    ) {
        $this->timestamp = $timestamp === 0.0 ? microtime(true) : $timestamp;
    }
}

Key Design Decisions:

• Uses float timestamps (not DateTime objects) to match existing project patterns
• Default parameter allows existing code to work unchanged
• Explicit timestamp parameter enables deserialization with preserved values
• Backward compatibility: missing timestamps in old data default to 0.0 → auto-generates current time

Test Coverage

New Tests:

• GateEvaluationTest.php - 7 tests covering timestamp behavior
• ActionSkipTest.php - 7 tests covering timestamp behavior
• TransitionContextSerializationTest.php - 5 new tests for timestamp serialization

Total Test Count: 347 tests (up from 328)
Code Coverage: 100% maintained

Test Plan

• All 347 tests pass
• 100% code coverage maintained
• make check passes (lint + quality + tests)
• PHPStan baseline updated for removed redundant type assertions
• Backward compatibility verified (old serialized data loads)

Benefits

✅ Observability - Know when gates evaluated and actions skipped
✅ Debugging - Correlate workflow timing with logs
✅ Analysis - Measure gate evaluation duration
✅ Consistency - Matches existing Event timestamp pattern
✅ Backward Compatible - Existing code continues to work

Closes #22

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