fix(logging): row 71 — stop logging the standby's by-design active-node verdict at ERROR

A healthy standby logged "Health check active-node with status Unhealthy …
'not the site pair primary (standby)'" at Error on every probe — every 10s on a
site node, and (discovered while fixing this) every 5s on a central standby,
which Traefik health-probes at that cadence. Correct-by-design state at an
alarming severity: it floods the log and trains operators to ignore ERR.

Mechanism: DefaultHealthCheckService logs one line per check per probe and picks
the level from the verdict — Debug/Warning/Error for Healthy/Degraded/Unhealthy.
Both active-node checks answer Unhealthy on the standby because 503 IS the
contract /health/active publishes. There is no IHealthCheckPublisher in this
repo, so each line is one inbound HTTP probe.

Fix: one Serilog exclusion filter in LoggerConfigurationFactory. A level
override could not work — Serilog's MinimumLevel.Override only RAISES a
per-source floor, and a LogEvent's Level is immutable, so neither an override
nor an enricher can rewrite Error as Information. Changing the check to report
Degraded was rejected: it would alter the HTTP status that /health/active
publishes, which is load-bearing for Traefik and the family dashboard.

The constraint (genuine failures must still log at Error) is preserved by keying
the predicate on the check NAME rather than the logger category: localdb,
akka-cluster, database and required-singletons keep their Error lines, and the
active-node check has no error path of its own — the active node always answers
Healthy — so the only event this can ever suppress is a standby reporting that
it is a standby. The verdict stays fully observable via /health/active's own
HTTP status, the readiness probe's cluster view, and the health dashboard.

Also corrects a stale CLAUDE.md claim found while verifying what consumes this
check: "/health/active is central-only (site nodes map no /health/* at all)" is
wrong — SiteServiceRegistration registers akka-cluster + localdb + the
role-scoped SitePairActiveNodeHealthCheck, and Program.cs's Site branch calls
MapZbHealth() on the HTTP/1.1 listener.

Fail-before evidence: with the filter behaviourally disabled,
StandbyActiveNodeVerdict_IsNotLogged fails "Collection was not empty" while the
other 9 tests in the file — the must-still-log constraints — pass either way,
which is what proves the filter is narrow rather than a blanket suppression.

Tests: Host 518 green (10 new).

CLAUDE.md

@@ -83,7 +83,7 @@ spec for each is `docs/requirements/Component-<Name>.md`, and `README.md` carrie
   - `site_events.id` changed from autoincrement INTEGER to an application-minted **GUID**. Last-writer-wins keys on the primary key, so two nodes independently minting `id=1,2,3…` would destroy each other's events rather than merge them. The event-log read path uses a composite `(timestamp, id)` keyset cursor with an **opaque string** continuation token; `EventLogEntry.Id` and both `ContinuationToken`s are `string`/`string?` on the site↔central Akka DTOs.
   - `ScadaBridge:OperationTracking:ConnectionString`, `ScadaBridge:SiteEventLog:DatabasePath` and — as of Phase 2 — `ScadaBridge:StoreAndForward:SqliteDbPath` + `ScadaBridge:Database:SiteDbPath` are all **migration-only** — nothing reads them but `SiteLocalDbLegacyMigrator`, which copies a pre-Phase-1 file in once (deterministic `mig-{NodeName}-{legacyId}` event ids, `INSERT OR IGNORE`, runs AFTER `RegisterReplicated` so migrated rows replicate) and renames it `.migrated`. Delete the keys once a node has migrated.
   - This incidentally fixes a data-loss bug: both legacy databases defaulted to CWD-relative paths **outside** the mounted volume and were discarded on every container recreate.
-  - **Replication is default-OFF and opt-in** via `LocalDb:Replication:PeerAddress` + a matching `ApiKey` on both nodes. `LocalDbSyncAuthInterceptor` is **fail-closed**: no configured key means no sync stream is accepted at all, so a key typo does not degrade to unauthenticated replication — the pair simply stops converging. The sync endpoint shares the existing site gRPC h2c listener (8083); no new port. Rig posture: **site-a replicated, site-b/site-c deliberately not**, so both states are proven side-by-side. Status surfaces on the site health report as `LocalDbReplicationConnected` / `LocalDbOplogBacklog` (both nullable — null means "no data", NOT "disconnected with an empty backlog") and as `localdb_*` Prometheus series. **A transient backlog spike is expected daily and is not a fault:** the `site_events` retention purge (and the storage-cap trim) is CDC-captured like any other write — there is deliberately no purge-exemption path — so the backlog jumps by the deleted batch size and drains as the peer acks it; the purge logs an Information note saying so on a replication-enabled node (`SiteEventLogReplicationCheck`, supplied by the Host from `SiteLocalDbSetup.ReplicationIsConfigured` so SiteEventLogging never reads LocalDb config itself). Healthy = `LocalDbReplicationConnected` stays true and the backlog returns to ~0; see `docs/deployment/topology-guide.md` → *Reading the replication backlog*. Note `ZbTelemetryOptions.Meters` is an **allowlist** (`SiteServiceRegistration.ObservedMeters`); an unlisted meter exports nothing, silently.
+  - **Replication is default-OFF and opt-in** via `LocalDb:Replication:PeerAddress` + a matching `ApiKey` on both nodes. `LocalDbSyncAuthInterceptor` is **fail-closed**: no configured key means no sync stream is accepted at all, so a key typo does not degrade to unauthenticated replication — the pair simply stops converging. The sync endpoint shares the existing site gRPC h2c listener (8083); no new port. Rig posture: **site-a replicated, site-b/site-c deliberately not**, so both states are proven side-by-side. Status surfaces on the site health report as `LocalDbReplicationConnected` / `LocalDbOplogBacklog` (both nullable — null means "no data", NOT "disconnected with an empty backlog") and as `localdb_*` Prometheus series. **An UNCONFIGURED node reports null for both** — the code only started matching that documented contract with register row 80: the engine is registered unconditionally and answers `Connected=false`/`0` while inert, and publishing that made site-b/site-c look like broken replicated sites and starved central's null branches (row 33's conditional KPI emission + sustained-badge anchor exclusion) of the null they exist for. `LocalDbReplicationStatusReporter` now gates on a Host-supplied `SiteLocalDbSetup.ReplicationIsConfigured` flag, so `false` means exactly one thing: **configured, peer session down** = a real fault. Watch the trap that caused it — configured-ness is `PeerAddress` **OR** `ApiKey`, so "no PeerAddress" is NOT "unreplicated" (the pre-existing Host wiring test fixture is a passive-half replicated node for precisely this reason). **A transient backlog spike is expected daily and is not a fault:** the `site_events` retention purge (and the storage-cap trim) is CDC-captured like any other write — there is deliberately no purge-exemption path — so the backlog jumps by the deleted batch size and drains as the peer acks it; the purge logs an Information note saying so on a replication-enabled node (`SiteEventLogReplicationCheck`, supplied by the Host from `SiteLocalDbSetup.ReplicationIsConfigured` so SiteEventLogging never reads LocalDb config itself). Healthy = `LocalDbReplicationConnected` stays true and the backlog returns to ~0; see `docs/deployment/topology-guide.md` → *Reading the replication backlog*. Note `ZbTelemetryOptions.Meters` is an **allowlist** (`SiteServiceRegistration.ObservedMeters`); an unlisted meter exports nothing, silently.
   - Design: **scadaproj** `docs/plans/2026-07-19-scadabridge-localdb-design.md` (that doc lives in the umbrella repo, not here); Phase 1 plan + Phase 2 gate are here under `docs/plans/`. Phase 2 **deleted** `SiteReplicationActor`, its `ReplicationMessages`, StoreAndForward's `ReplicationService`, and `StoreAndForwardStorage.ReplaceAllAsync` — do not reintroduce them:
 
     - CDC replication does all three jobs now: config deploys reach the standby as ordinary row changes — **the standby makes no fetch at all** during a deploy (`SiteReconciliationActor`'s node-STARTUP fetch when central reports gaps is a different, surviving path) — and buffer mutations replicate via triggers on `sf_messages`. `ReplaceAllAsync` was a destructive delete-all-then-insert-all resync and is **unsafe to reintroduce**: a mass DELETE on a replicated table would be captured and shipped to the peer. LocalDb's snapshot resync merges per row under LWW and never deletes, which is also why the old N1 directional-authority guard is gone — there is no wipe left to gate.
@@ -180,7 +180,7 @@ spec for each is `docs/requirements/Component-<Name>.md`, and `README.md` carrie
 - Failure detection: 2s heartbeat, 10s threshold. Total failover ~25s (drill-measured 2026-07-21 under auto-down: active-crash TAKEOVER in 28s, standby-crash removal in 27s with 0 routing blips — `docker/failover-drill.sh`).
 - CoordinatedShutdown for graceful singleton handover.
 - Automatic dual-node recovery from persistent storage.
-- **Active/standby is decided by `ActiveNodeEvaluator.SelfIsOldestUp`, never by cluster leadership** — see the Architecture note above. `/health/active` is **central-only** (site nodes map no `/health/*` at all) and backs both Traefik's active-node routing and `IActiveNodeGate`, so the proxy and the Inbound API always agree on which node is active. Central reaches a site by dialling `GrpcNodeAAddress`/`GrpcNodeBAddress` explicitly and flipping on error; whichever node answers, the site-internal `ClusterSingletonProxy` lands the work on the active node for free, so central still never needs to track which *site* node is active.
+- **Active/standby is decided by `ActiveNodeEvaluator.SelfIsOldestUp`, never by cluster leadership** — see the Architecture note above. **Central's** `/health/active` backs both Traefik's active-node routing and `IActiveNodeGate`, so the proxy and the Inbound API always agree on which node is active. **Site nodes DO map `/health/*` too** — the "site nodes map no `/health/*` at all" claim that stood here was stale: `SiteServiceRegistration` registers `akka-cluster` + `localdb` (Ready) and `SitePairActiveNodeHealthCheck` (Active, role-scoped to `site-{SiteId}`, deliberately NOT central's unscoped shared check), and `Program.cs`'s Site branch calls `MapZbHealth()` on the HTTP/1.1 listener so the family overview dashboard can probe every node identically. Nothing in this repo probes a site's `/health/active` (Traefik health-probes central only), and there is **no `IHealthCheckPublisher` anywhere**, so those checks run only on an inbound HTTP probe. Consequence worth knowing: the standby's correct-by-design `active-node` Unhealthy verdict is logged by `DefaultHealthCheckService` at **Error** on every probe, which `LoggerConfigurationFactory` now suppresses with one narrowly-keyed Serilog filter (register row 71 — see `Component-Host.md` → *Standby health-check log noise*; genuine failures of every other check still log at Error). Central reaches a site by dialling `GrpcNodeAAddress`/`GrpcNodeBAddress` explicitly and flipping on error; whichever node answers, the site-internal `ClusterSingletonProxy` lands the work on the active node for free, so central still never needs to track which *site* node is active.
 - **Seed-node ordering: every node lists ITSELF first (decision 2026-07-22) — the boot-alone gap is CLOSED.** Only `seed-nodes[0]` may self-join to form a new cluster (Akka runs `FirstSeedNodeProcess` for it, `JoinSeedNodeProcess` — which can never form one — for everyone else). All 14 shipped node appsettings now lead with the node's own address, so any node can cold-start alone and become operational unattended (~5s, `seed-node-timeout`); `StartupValidator` fails the boot if the ordering is broken (compares host AND port; Akka does no DNS canonicalisation). Two nodes cold-starting together while mutually reachable converge on ONE cluster via the `InitJoin` handshake — they split only under a genuine boot-time partition, the same class auto-down accepts. **An external self-form timer (`Cluster.Join(SelfAddress)` after a window) was implemented and REJECTED:** it sits outside the join handshake, so on a routine standby restart — where the peer is alive but the join is stalled behind removal of the node's own stale incarnation — it fires mid-join and permanently splits the pair (measured: still split after 90s). Regression tests: `SelfFirstSeedBootstrapTests`. The keep-oldest active-crash total outage was separately closed by the auto-down decision. See `docs/requirements/Component-ClusterInfrastructure.md` → Seed Node Ordering.
 - **Simultaneous-cold-start split-brain guard (opt-in, Gitea #33) — the residual self-first cost, closed.** Self-first-on-both means a *truly simultaneous* cold start (shared power/hypervisor event) races `FirstSeedNodeProcess` on BOTH nodes → two 1-node clusters that never merge (in-process loopback tests converge and hide it; real parallel VM starts don't — OtOpcUa reproduced it live). Ported from OtOpcUa (`lmxopcua` `d1dac87f`): a **dark switch `ScadaBridge:Cluster:BootstrapGuard:Enabled` (default OFF, guard-off byte-identical)**. On: `BuildHocon` emits an EMPTY seed list (Akka does not auto-join) and `ClusterBootstrapCoordinator` (`IHostedService`, registered in BOTH the Central and Site composition roots) issues ONE reachability-gated `JoinSeedNodes` — the pure `ClusterBootstrapGuard` core makes the lower canonical `host:port` the **founder** (self-first, forms immediately), the higher node TCP-probes the founder up to `PartnerProbeSeconds` (25s) and joins **peer-first** if reachable else **self-first** (cold-start-alone preserved). Decided BEFORE a single join, **never re-forms mid-handshake** (that was the rejected self-form-timer's flaw); case-insensitive founder tie-break; probe timings validated `>0` when enabled. Residual accepted trade: founder dies in the probe→join window → higher node hangs unjoined, coordinator WARNs, a restart recovers it. Tests: `ClusterBootstrapGuardTests` (pure) + `ClusterBootstrapCoordinatorTests` (real-ActorSystem, incl. both-cold-start-together-form-one-cluster). **ENABLED on the docker rig (all 8 nodes) 2026-08-02** after `deploy.sh`'s simultaneous recreate split site pairs twice on 2026-08-01 with the guard off; live gate PASS — two consecutive simultaneous-start trials (a full redeploy + a full-topology `docker compose restart`), all four pairs converged (every lower-address node founded self-first, every higher node probed-then-joined peer-first), zero splits. Default remains OFF elsewhere (wonder-app-vd03, docker-env2, Host defaults). See `docs/requirements/Component-ClusterInfrastructure.md` → Simultaneous cold start.