Auto: ablegacy-4 — indirect/indexed addressing parser

Closes #247

src/ZB.MOM.WW.OtOpcUa.Driver.AbLegacy/AbLegacyDriver.cs

@@ -438,6 +438,15 @@ public sealed class AbLegacyDriver : IDriver, IReadable, IWritable, ITagDiscover
             ?? throw new InvalidOperationException(
                 $"AbLegacy tag '{def.Name}' has malformed Address '{def.Address}'.");
 
+        // TODO(#247): libplctag's PCCC text decoder does not natively accept the bracket-form
+        // indirect address. Resolving N7:[N7:0] requires reading the inner address first, then
+        // rewriting the tag name with the resolved word number, then issuing the actual read.
+        // For now we surface a clear runtime error rather than letting libplctag fail with an
+        // opaque parser error.
+        if (parsed.IsIndirect)
+            throw new NotSupportedException(
+                $"AbLegacy tag '{def.Name}' uses indirect addressing ('{def.Address}'); runtime resolution is not yet implemented.");
+
         var runtime = _tagFactory.Create(new AbLegacyTagCreateParams(
             Gateway: device.ParsedAddress.Gateway,
             Port: device.ParsedAddress.Port,