Nine drivers raise IRediscoverable.OnRediscoveryNeeded when they observe that
a remote's tag set may have changed — a Galaxy redeploy, a TwinCAT
symbol-version bump, an MTConnect agent restart, a Sparkplug rebirth. Nothing
in src/ subscribed, so every raise went into the void. Drivers even wrap the
invoke in try/catch for "subscriber threw"; there has never been a subscriber.
DriverInstanceActor now attaches the event in PreStart and detaches in
PostStop, mirroring AttachAlarmSource/DetachAlarmSource. Attach is per-actor,
not per-connect: the raise has no connection affinity and can land while the
driver is between connects. The detach is load-bearing rather than tidy — the
IDriver instance outlives the actor when the host respawns a child around the
same driver object, so a missing -= accumulates one handler per respawn, each
holding a dead Self.
The signal rides the existing driver-health snapshot to /hosts as a
"re-browse" chip. It is ADVISORY: the served address space is deliberately not
rebuilt, because v3 authors raw tags explicitly through the /raw
browse-commit flow and a runtime graft would materialise nodes no operator
approved and no deployment artifact records.
Two things worth knowing:
- PublishHealthSnapshot dedups on a health fingerprint, and a rediscovery
raise on an otherwise-healthy driver changes none of the four fields it
hashed. Without adding the timestamp to that tuple the dedup swallows the
exact publish carrying the signal. Reverting that one line turns 3 of the 5
new tests red, which is how it was confirmed rather than assumed.
- The new test stub implements IDriver from scratch instead of deriving from
the shared StubDriver, whose GetHealth() returns DateTime.UtcNow — its
fingerprint differs on every call, so the dedup never engages and the dedup
test would have passed vacuously either way.
The planned discovery-result drift detector was NOT built. Modbus, S7, MQTT,
AbLegacy and Sql all echo authored config from DiscoverAsync rather than
browsing the device, so a discovered-vs-authored diff is permanently empty for
them — it would have been another plausible-looking inert seam, which is the
class this audit exists to remove. IRediscoverable is the trustworthy signal
because the driver asserts it deliberately.
DriverHealthChanged, IDriverHealthPublisher.Publish and HostsDriverRow gain
defaulted optional parameters, so no existing call site changed. telemetry.proto
gains fields 8/9 and both Phase-5 mappers carry them.
Runtime.Tests 512 passed / 31 skipped.
Option A from the issue — the cheap consistency check, no interface change.
The desired ref set was re-applied on a Connected TRANSITION (`ResubscribeDesired`)
and on a deploy's `SetDesiredSubscriptions`, and nowhere else. A subscription lost
while the driver STAYED Connected — a subscribe that failed and was never retried,
a handle dropped down an error path — left the actor subscribed to nothing while
still reporting Healthy, indefinitely.
`ReconcileSubscription` now rides the existing 30 s `health-poll` tick: while
Connected, a driver holding a desired set but no live handle is re-subscribed.
Gated on `ISubscribable`. A driver that cannot subscribe at all can still be handed
a desired set, and without the guard it would be told `Subscribe` every tick and
fail every tick, forever.
This is a state-machine consistency check, NOT a probe — it can only see that this
actor holds no handle, never that a handle is present but dead server-side, because
`ISubscriptionHandle` is opaque. That is option B, and it stays deferred until a
real occurrence shows the handle outliving the subscription; it would need a
liveness member implemented across all eight drivers with different subscription
mechanics.
A redundant `Subscribe` is possible (a tick queued ahead of an already-queued one
observes the same no-handle state) and is harmless: `HandleSubscribeAsync` is a
`ReceiveAsync`, so no tick is processed mid-subscribe, and it drops any prior
subscription before establishing the new one. Suppressing it would need a
pending-subscribe flag threaded through every self-tell site — more state than the
race is worth.
`healthPollInterval` becomes an optional Props parameter, mirroring the existing
`rediscoverInterval` seam, so a test can drive the reconcile without waiting 30 s.
Three tests. The reconcile itself is proven by a stub whose FIRST subscribe throws:
nothing else would ever retry it, so a second attempt can only come from the
reconcile — disabling `ReconcileSubscription` turns it red. The two guard tests are
absence assertions and are bounded by a positive control rather than a sleep: a
counting health publisher makes ticks PROCESSED observable, so "still one subscribe"
means the reconcile ran and declined, not that the timer had not fired.
Explicitly not deploy-time drift (#486) — re-asserting an already-correct desired
set would not have helped there.
Joseph Doherty