A deterministic PLC refusal (object does not exist, address out of range,
type inconsistent...) degraded driver health, and an all-refused driver (a
wrong DB number) sat Degraded with LastSuccessfulRead frozen, so the 90 s
comms-loss watchdog reconnected it forever against a reachable PLC.
- IsRefusal / IsAccessDenied classify over the whole exception chain. Live
probe on the snap7 fixture: S7.Net's READ paths raise the item error as a
BARE Exception ("Received error from PLC: ..."), its write paths as
PlcException(WriteData). The old PlcException-only match missed the read
shape entirely, so a real read access-denied was BadCommunicationError +
Degraded instead of the Faulted PUT/GET alert; the Test Connect probe had
the same blind spot.
- A refusal (read or write) is BadDeviceFailure with a once-per-tag Warning,
no health write and no reopen; it counts as answered, so it advances
LastSuccessfulRead and restores Healthy after a comms fault. An undecodable
buffer (S7ValueRangeException) also counts as answered.
- A write batch the CPU answered without a failure advances
LastSuccessfulRead and retires a Degraded the write side itself published.
- Tests that used ReadData as their generic "device fault" now use SendData
so their Degraded leg is still exercised.
Refs #742
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
Joseph Doherty
a1f20e78f9