The S7 Plc was opened once in InitializeAsync and never re-opened: a transient
PLC reboot / network blip permanently killed the driver until redeploy. Introduce
an IS7Plc / IS7PlcFactory seam (mirrors TwinCAT's ITwinCATClientFactory) and a lazy
EnsureConnectedAsync that disposes a dead handle and re-opens a fresh connection on
the next data call. Reads/writes mark the handle dead on a connection-fatal fault
(socket drop / ErrorCode.ConnectionError) but NOT on a data-address error; the probe
loop routes through EnsureConnectedAsync as a backstop.
The seam also closes the S7 TEST-1 gap — the reconnect state machine is now unit-
testable without a live PLC (S7.Net.Plc is sealed with no in-process fake).
Verification:
- 4 deterministic unit guards (fatal→reopen, data-error→no-reopen, raw socket→reopen,
reopen-fail→degrade-then-recover); full S7 unit suite 234/234 green.
- LIVE end-to-end proof against real python-snap7 (S7_1500ReconnectTests, double-gated
on sim reachability + S7_RECONNECT_BOUNCE_CMD): bounced the container, driver observed
the outage and resumed Good reads with NO redeploy. Baseline smoke 3/3 still green.
Joseph Doherty