Fixes concurrent manager creation races that caused SafeOpenErrors during session export.
Deduplicates in-flight manager creation so only one full QMD manager arms per agent/config at a time, eliminating the concurrent exportSessions() collisions that triggered path changed during write errors
Resolves and snapshots runtime inputs before cache reuse, replacing stale managers atomically when workspace/config changes, and aborting queued export work promptly on close()
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