The old probe did a subscribe-read-unsubscribe cycle every 5 seconds to
check connection health. This created unnecessary churn and didn't detect
the failure mode where long-lived subscriptions silently stop receiving
COM callbacks (e.g. stalled STA message pump). The new approach keeps a
persistent subscription on the health check tag and forces reconnect if
no value update arrives within a configurable threshold (ProbeStaleThresholdMs,
default 5s). Also adds STA message pump debug logging (5-min heartbeat with
message counters) and fixes log file path resolution for Windows services.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
