fix(db): classify non-SqlException DB outages as transient; propagate cancellation (#7)

ExecuteWriteAsync only caught SqlException, so a live outage surfacing as
InvalidOperationException/SocketException/IOException/TimeoutException escaped
unclassified and crashed the script actor instead of buffering. Mirror the HTTP
path: propagate OperationCanceledException on cancellation, classify transport
exceptions as transient (buffer+retry), let unexpected exceptions propagate.

tests/ZB.MOM.WW.ScadaBridge.ExternalSystemGateway.Tests/SqlErrorClassifierTests.cs

@@ -1,3 +1,5 @@
+using System.Data.Common;
+
 namespace ZB.MOM.WW.ScadaBridge.ExternalSystemGateway.Tests;
 
 /// <summary>
@@ -62,4 +64,42 @@ public class SqlErrorClassifierTests
         // be silently retried forever. Unknown => permanent => false.
         Assert.False(SqlErrorClassifier.IsTransient(errorNumber));
     }
+
+    // ── M2.3 (#7) code-review fix: IsTransient(Exception) — a live DB outage does
+    //    not always surface as a SqlException. Transport/connection/timeout/driver
+    //    exception types are transient (buffer+retry), mirroring the HTTP path's
+    //    ErrorClassifier.IsTransient(Exception). ──
+
+    public static IEnumerable<object[]> TransientExceptionTypes()
+    {
+        yield return new object[] { new InvalidOperationException("connection not open") };
+        yield return new object[] { new System.IO.IOException("transport reset") };
+        yield return new object[] { new System.Net.Sockets.SocketException(10060) };
+        yield return new object[] { new TimeoutException("timed out") };
+        yield return new object[] { new TaskCanceledException("driver-level cancellation") };
+        // Any DbException that is NOT a SqlException is a driver/transport error.
+        yield return new object[] { new NonSqlDbException("provider transport error") };
+    }
+
+    [Theory]
+    [MemberData(nameof(TransientExceptionTypes))]
+    public void IsTransient_Exception_TrueForTransportTypes(Exception ex)
+    {
+        Assert.True(SqlErrorClassifier.IsTransient(ex));
+    }
+
+    [Fact]
+    public void IsTransient_Exception_FalseForUnexpectedType()
+    {
+        // Authoring bugs are NOT a DB outage — they must propagate, exactly as the
+        // HTTP path lets genuinely-unexpected exceptions escape its IsTransient filter.
+        Assert.False(SqlErrorClassifier.IsTransient(new ArgumentException("authoring bug")));
+        Assert.False(SqlErrorClassifier.IsTransient(new NullReferenceException()));
+    }
+
+    /// <summary>A concrete <see cref="DbException"/> that is not a SqlException, for the classifier unit test.</summary>
+    private sealed class NonSqlDbException : DbException
+    {
+        public NonSqlDbException(string message) : base(message) { }
+    }
 }