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fix(ab): a refused operation is BadNotSupported, not a comms fault (Task 22 review r1; closes #571)

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Native is the default, so a locally refused write must not look like a comms fault.

- AbLegacy: an AbTransportException with AbStatus.Unsupported (status-bit sub-element writes, PLC-5
  non-N reads, all PLC-5 writes; libplctag's ErrorUnsupported maps here too) now returns
  BadNotSupported on both the read and the write path (incl. the bit-RMW path). The tag handle is
  not evicted and driver health is not touched. A native runtime whose init read is refused locally
  is CACHED rather than disposed, so a poll of a refused tag does not re-create (and re-lease the
  pooled connection) every cycle.
- AbCip: the same mapping on the write path and both read paths (single + whole-UDT).
- Uses the existing named BadNotSupported constants (StatusCodeParityTests guard).
- Tests (falsified by disabling the mapping, and separately the keep-on-refusal): status-bit
  writes and PLC-5 read/write through the driver over the native runtime — BadNotSupported, zero
  wire requests, one create, health unchanged; AbCip refused read/write via a refusing fake plus a
  control that a non-refusal failure still evicts and degrades.
- Docs/CLAUDE.md: BadNotSupported; #571 known-gap wording removed.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe
This commit is contained in:
Joseph Doherty
2026-10-07 21:12:08 -04:00
parent 1806af54f0
commit 39ae286cd7
7 changed files with 279 additions and 60 deletions
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CLAUDE.md
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@@ -984,7 +984,7 @@ CLI share them) — except an AbLegacy driver with any PLC-5 / `LogixPccc` devic
"Default" is encoded by omitting the key; the AdminUI must never re-emit a concrete default. Evidence: AbCip
reads proven on a real CompactLogix (Z-35162, read-only); AbCip writes and all AbLegacy are `ab_server`-only.
Fall back with `"transport": "Libplctag"`. ⚠️ AbLegacy native refuses status-bit sub-element
writes (`T4:0.DN`…, client sees `BadCommunicationError`) and its ST byte order is unverified. Client-visible: native reports `BadTypeMismatch` where libplctag returned
writes (`T4:0.DN`…, client sees `BadNotSupported`; refusals never evict or degrade) and its ST byte order is unverified. Client-visible: native reports `BadTypeMismatch` where libplctag returned
Good garbage for a same-width mis-authored type (DINT authored, REAL returned). libplctag is confined to
`Libplctag*.cs` adapters by `LibplctagConfinementGuardTests`; do not reference it elsewhere. See
`docs/drivers/AbCip.md` §Transport, `docs/drivers/AbLegacy.md`, and