When OnDiskLoader creates temp directories for on-disk analyzer loading, cleanup relies on AssemblyLoadContext finalization -- which is not guaranteed to run. Over time, stale directories accumulate under the temp path.

Approach

Uses a file-lock sentinel to prove directory ownership:

• LogReaderState acquires a .lock file (FileShare.None) in its BaseDirectory on construction. The OS releases this lock automatically on process exit (even crashes).
• On construction, after acquiring its own lock, LogReaderState enumerates sibling directories in the same parent and calls CommonUtil.CleanupStaleTempDirectories() which probes each .lock file:
  • Lock acquirable or absent -- directory is stale -- delete recursively
  • Lock denied -- directory is in active use -- skip
• On Dispose(), the lock file is released and deleted so the directory can be cleaned by DeleteDirectoryIfEmpty or by the next invocation's cleanup pass.

This is self-contained in LogReaderState -- no explicit startup call needed. Any code path that creates a LogReaderState (CLI commands, library consumers) will automatically clean up stale siblings.

Other changes

• Added CommonUtil.GetCompilerLogTempDirectory(string? basePath = null) helper to centralize the temp directory path logic.
• Added unit tests covering stale deletion, locked-dir skip, and missing-lock scenarios.
• Added end-to-end test ReplayOnDiskCleansStaleTempDirectories that verifies a second tool invocation cleans up the stale directory left by an on-disk analyzer run.