#365 HIGH: Global determinism state shared across workflows

## Issue Global flags in engine/durable_context.py:39-43 are NOT thread-safe and shared across all workflow executions: ```python _DETERMINISM_CHECK_ENABLED = False _determinism_violations: list[dict[str, Any]] = [] ``` ## Impact - Concurrent workflows share determinism state - False positives/negatives in determinism detection - Memory leaks from violations list growing - Violates Temporal's workflow isolation principle ## Location engine/durable_context.py:39-43 ## Fix Make determinism state per-workflow-run or per-context using context-local storage