fix(site-event-log): queries on own read connection off the actor thread, bounded keyword window; cap trim counts/vacuums rarely (review 2026-10-21 02/P1, 02/P4)

src/ZB.MOM.WW.ScadaBridge.SiteEventLogging/SiteEventLogger.cs

@@ -45,6 +45,7 @@ public class SiteEventLogger : ISiteEventLogger, IDisposable
     internal const int WriteBatchSize = 256;
 
     private readonly SqliteConnection _connection;
+    private readonly ILocalDb _localDb;
     private readonly ILogger<SiteEventLogger> _logger;
     private readonly object _writeLock = new();
     private readonly Channel<PendingEvent> _writeQueue;
@@ -80,6 +81,7 @@ public class SiteEventLogger : ISiteEventLogger, IDisposable
         ArgumentNullException.ThrowIfNull(localDb);
 
         _logger = logger;
+        _localDb = localDb;
 
         // Already open — CreateConnection returns a live, pragma-configured,
         // UDF-registered connection. Calling Open() on it again would throw.
@@ -141,6 +143,25 @@ public class SiteEventLogger : ISiteEventLogger, IDisposable
         }
     }
 
+    /// <summary>
+    /// Runs <paramref name="func"/> on a short-lived, dedicated READ connection that is
+    /// NOT serialised on the write lock. <c>site_events</c> lives in a WAL database, so a
+    /// reader never blocks the single writer (and vice versa): a slow central event-log
+    /// query (full-scan keyword search at the storage cap) can no longer stall the writer
+    /// loop's <c>FlushBatch</c> and overflow the bounded write queue (review 2026-10-21
+    /// 02/P1). The same pattern <c>OperationTrackingStore.GetStatusAsync</c> uses.
+    /// </summary>
+    /// <typeparam name="T">The return type of the function.</typeparam>
+    /// <param name="func">The function to run against the read connection.</param>
+    /// <returns>The value returned by <paramref name="func"/>.</returns>
+    internal T WithReadConnection<T>(Func<SqliteConnection, T> func)
+    {
+        ArgumentNullException.ThrowIfNull(func);
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        using var readConnection = _localDb.CreateConnection();
+        return func(readConnection);
+    }
+
     /// <summary>
     /// Runs <paramref name="func"/> against the shared connection while holding the
     /// write lock. Throws <see cref="ObjectDisposedException"/> if the logger has