`IHostConnectivityProbe` was a dead surface: eleven drivers implement it, `GetHostStatuses()`
had ZERO production call sites, and `OnHostStatusChanged` had no subscriber outside the Galaxy
driver's own aggregator. Per-host connectivity was computed by every driver and read by nobody.
The issue offered "build the publisher or delete it". The publisher as its entity doc described
it — driver nodes upserting `DriverHostStatus` rows — is not buildable: per-cluster mesh Phase 4
gates `AddOtOpcUaConfigDb` on the `admin` role, so a driver-only node has no ConfigDb connection
to write rows with. So the capability is kept and the transport changed.
`DriverHealthChanged.HostStatuses` now carries the probe result to `/hosts` as a Hosts column.
That channel already reached the page, already survives the mesh split via the Phase 5 gRPC
telemetry stream, and already replays a last-value snapshot on re-subscribe — so per-host state
re-primes after a reconnect without a durable store. Both halves of the interface finally do
what they are for: the event triggers a prompt publish, the pull is the source of truth.
The point of the column is the case the driver-level state chip structurally cannot express: a
multi-device driver stays aggregate-Healthy while ONE of its devices is unreachable.
Two traps, both pinned by tests that were falsified against the prod code:
- The host digest MUST be in the publish fingerprint. On a single-host-down transition every
other fingerprint component is unchanged, so the dedup would swallow exactly the publish
carrying the news — the trap that already bit the rediscovery signal. Removing it turns the
guard test red, verified.
- null (no probe) must stay distinct from empty (probe with no hosts). proto3 cannot tell an
absent repeated field from an empty one, hence the explicit `has_host_statuses` flag;
collapsing them would render every probe-less driver as one whose devices are all fine.
Dropped: the DriverHostStatus entity, enum, DbSet, model config and table (migration
DropDriverHostStatusTable — empty on every deployment, so the scaffolder's data-loss warning is
moot, and Down() recreates it exactly).
Found en route, NOT fixed here: `DriverInstanceResilienceStatus` is the identical defect — no
writer, no reader, only a DbSet declaration, while the live data rides the
`driver-resilience-status` telemetry channel. Its doc-comment now states that rather than
describing the sampler and AdminUI join that were never built. Filed as #524 rather than widening
this schema change beyond what was asked.
Claude-Session: https://claude.ai/code/session_015p7wGqy3YpZNCpDzTpGMKo
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.
Joseph Doherty