test(ab): default AB matrices to one profile when unset; PLC-5/status-bit refusal fixture tests (#594, #593)

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests/TransportMatrix.cs

@@ -7,7 +7,10 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.IntegrationTests;
 /// <remarks>
 ///     Preserves the <c>AB_LEGACY_COMPOSE_PROFILE</c> filter the smoke theory always applied: when set,
 ///     <see cref="KnownProfiles.All"/> is narrowed to that profile <b>before</b> it is crossed with the
-///     transports, so the rows match the running container.
+///     transports, so the rows match the running container. Unset, every family is crossed because each
+///     has its own port and skips itself when unreachable — <b>unless</b> <c>AB_LEGACY_ENDPOINT</c> pins
+///     one device, in which case the family is a property of that device and cannot be detected, so only
+///     the default SLC500 profile is crossed (set <c>AB_LEGACY_COMPOSE_PROFILE</c> to pick another).
 /// </remarks>
 public static class TransportMatrix
 {
@@ -21,6 +24,9 @@ public static class TransportMatrix
         get
         {
             var only = Environment.GetEnvironmentVariable("AB_LEGACY_COMPOSE_PROFILE");
+            if (string.IsNullOrEmpty(only) &&
+                Environment.GetEnvironmentVariable("AB_LEGACY_ENDPOINT") is { Length: > 0 })
+                only = KnownProfiles.Slc500.ComposeProfile;
             return from p in KnownProfiles.All
                    where string.IsNullOrEmpty(only) ||
                          string.Equals(p.ComposeProfile, only, StringComparison.OrdinalIgnoreCase)