fix(modbus): equipment tags carry unitId; ResolveHost keys per-unit via the resolver (CONV-4)

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Modbus/ModbusDriver.cs

@@ -140,10 +140,19 @@ public sealed class ModbusDriver
             WriteHealth(new DriverHealth(DriverState.Degraded, current.LastSuccessfulRead, ex.Message));
     }
 
-    /// <inheritdoc />
+    /// <summary>
+    ///     Resolve a reference to the per-slave host key (<c>host:port/unitN</c>) that keys its
+    ///     per-host resilience (bulkhead / circuit breaker). CONV-4: routes through
+    ///     <see cref="EquipmentTagRefResolver{TDef}"/> so an equipment-tag reference (raw TagConfig
+    ///     JSON) keys its OWN authored unit — via the tag's optional <c>unitId</c> or the driver
+    ///     default — rather than the single-slave fallback. The resolver caches parses, so this adds
+    ///     no per-call cost after first use.
+    /// </summary>
+    /// <param name="fullReference">The tag reference (authored name or equipment-tag JSON).</param>
+    /// <returns>The per-slave host key.</returns>
     public string ResolveHost(string fullReference)
     {
-        if (_tagsByName.TryGetValue(fullReference, out var tag))
+        if (_resolver.TryResolve(fullReference, out var tag))
             return BuildSlaveHostName(ResolveUnitId(tag));
         // Unknown reference — fall back to driver-instance host (single-slave behaviour).
         return HostName;