Move subscribe/unsubscribe I/O outside lock(Lock) in SyncAddressSpace to avoid
blocking all OPC UA operations during rebuilds. Replace blocking ReadAsync calls
for alarm priority/description in dispatch loop with cached subscription values.
Extract IHistorianConnectionFactory so EnsureConnected can be tested without the
SDK runtime — adds 5 connection lifecycle tests (failure, timeout, reconnect,
state resilience, dispose-after-failure). All stability review findings and test
coverage gaps are now fully resolved.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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