Code review on T10-T12 bundle (commits 0cf86bb/00bb030/0405947 + audit
fix 76e1a64) found 3 Important issues:
1. LandblockStreamer.Start() had an idempotency race — the XML doc
claimed thread-safety but the implementation checked _worker != null
before assigning, allowing two callers to both pass the check and
spawn duplicate worker threads. Fixed via Interlocked.CompareExchange.
2. No test verified the worker emits Failed when buildMeshOrNull returns
null. Added Load_WhenBuildMeshReturnsNull_ReportsFailed.
3. StreamingControllerTests.cs:81 used MeshData: default! when
constructing a Loaded result. If a future test flows MeshData
through the apply callback, the null reference would NRE rather
than producing a meaningful assertion failure. Replaced with a real
empty LandblockMeshData instance.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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