A first-touch native write to a T/C/R status-bit sub-element (T4:0.DN) created
and initialised the tag's runtime before the runtime's write refusal could fire;
the init is one READ, so against a device lacking the file (the ab_server
fixture has no T/C/R) it surfaced as BadCommunicationError + Degraded health
instead of BadNotSupported. The bit-RMW path was not involved: AbLegacyAddress
rejects sub-element + /N, so a status bit's BitIndex is always null.
NativeAbLegacyTagRuntime.WriteRefusal is now the single predicate (status bit
by address whatever the authored type; any PLC-5 write), asked by the driver via
IAbLegacyTagFactory.WriteRefusal (default null, so libplctag is unchanged)
before EnsureTagRuntimeAsync and ahead of the bit-RMW branch.
Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe
Joseph Doherty