fix(log): prevent sink destruction caused by backend exceptions (#4694)

src/logging.cpp

@@ -15,6 +15,7 @@
 #include <boost/log/expressions.hpp>
 #include <boost/log/sinks.hpp>
 #include <boost/log/sources/severity_logger.hpp>
+#include <boost/log/utility/exception_handler.hpp>
 
 // local includes
 #include "logging.h"
@@ -168,6 +169,11 @@ namespace logging {
     sink->set_filter(severity >= min_log_level);
     sink->set_formatter(&formatter);
 
+    // Prevent the async sink's background thread from dying on backend exceptions.
+    // Without this, a single I/O error (disk full, file locked, broken stdout, etc.)
+    // kills the thread and all subsequent log records are silently lost.
+    sink->set_exception_handler(bl::make_exception_suppressor());
+
     // Flush after each log record to ensure log file contents on disk isn't stale.
     // This is particularly important when running from a Windows service.
     sink->locked_backend()->auto_flush(true);