fix(runtime): pin the Primary-verdict member-event subscription with a test; document the pre-join allow window (review R6 MINOR-2/3)

MINOR-3: new DriverHostActorPrimaryRoleSourceTests case drives the
deny flip with a real ClusterEvent.MemberUp on the EventStream (how the
cluster's domain-event publisher reaches a Cluster.Subscribe subscriber)
instead of a direct RepublishPrimaryVerdict tell; it fails when the
Cluster.Subscribe(IMemberEvent) call is deleted.

MINOR-2: the published verdict MIRRORS the live gate; before this node has
joined its member count is 0 and both allow (seconds; up to the bootstrap
guard's 25 s probe), so the Sparkplug primary-host claim can be held on
both nodes in that window (native ack is unaffected - view and route
agree). Behaviour deliberately unchanged: denying until self is Up would
change the live gate too and delay writes/acks on a single-node cluster's
own join. Comments + AlarmTracking.md / Redundancy.md / Mqtt.md corrected.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

docs/Redundancy.md

@@ -526,7 +526,7 @@ Three data-plane surfaces are **Primary-gated** so a warm standby never touches
 
 Before archreview 03/S4 the unknown-role case defaulted to *allow* unconditionally, opening a dual-primary window: a freshly-booted secondary on a multi-node cluster serviced shared-device writes and emitted duplicate fleet-wide alerts for up to the ~10 s `RedundancyStateActor` heartbeat (and indefinitely if the snapshot's NodeId never matched this node). Membership is authoritative much earlier than DPS delivery, so an unknown role on a **multi-driver** cluster now default-**denies**. The driver member count is read live from `Cluster.State.Members` (Up members with the `driver` role); a non-cluster ActorRefProvider yields 0 ⇒ single-node posture. If a snapshot arrives that never mentions this node while a driver peer exists (the 03/S5 identity-mismatch shape), `DriverHostActor` logs a one-time Warning so the silent mismatch is diagnosable.
 
-**What a client sees during the boot window (multi-node, role unknown):** an inbound write is **rejected** (not queued — OT actuation seconds late is a surprise). The reject rides the sanctioned optimistic-write self-correction surface: the node reverts to its prior value with a transient Bad-quality blip and a Part 8 `AuditWriteUpdateEvent`; the client's synchronous write call still returned Good (exactly as any failed device write behaves since the #5 write-outcome self-correction). The rejection reason distinguishes the boot window (`"not primary (role unknown)"`) from a steady-state Secondary (`"not primary"`). Acks are dropped (Warning-logged when role-unknown) — and since review R1 m2 a native OPC UA Acknowledge is refused up front (`BadInvalidState`) in the same window: `DriverHostActor` publishes its Primary verdict to `IDriverPrimaryRoleSource` (the native-ack gate, and the MQTT Sparkplug primary-host claim) once at start and again on every cluster membership change, not only on redundancy snapshots, so the published verdict denies as soon as a driver peer is Up rather than sitting on the single-node "allow" seed until the first snapshot. The alerts emit is skipped (the Primary peer publishes the single fleet copy). The window closes on the first delivered snapshot.
+**What a client sees during the boot window (multi-node, role unknown):** an inbound write is **rejected** (not queued — OT actuation seconds late is a surprise). The reject rides the sanctioned optimistic-write self-correction surface: the node reverts to its prior value with a transient Bad-quality blip and a Part 8 `AuditWriteUpdateEvent`; the client's synchronous write call still returned Good (exactly as any failed device write behaves since the #5 write-outcome self-correction). The rejection reason distinguishes the boot window (`"not primary (role unknown)"`) from a steady-state Secondary (`"not primary"`). Acks are dropped (Warning-logged when role-unknown) — and since review R1 m2 a native OPC UA Acknowledge is refused up front (`BadInvalidState`) in the same window: `DriverHostActor` publishes its Primary verdict to `IDriverPrimaryRoleSource` (the native-ack gate, and the MQTT Sparkplug primary-host claim) once at start and again on every cluster membership change, not only on redundancy snapshots, so the published verdict denies as soon as a driver peer is Up rather than sitting on the single-node "allow" seed until the first snapshot. ⚠️ "As soon as a driver peer is Up" means **in this node's own cluster view**, i.e. after it has joined: the host is spawned before the join, when the view holds no members, and a member count of 0 takes the single-node *allow* posture — for the published verdict and the live gate alike. So a node cold-starting into a pair whose peer is already Primary allows until its own join completes (seconds normally; up to `Cluster:BootstrapGuard:PartnerProbeSeconds`, 25 s, under the bootstrap guard), and in that window the MQTT Sparkplug primary-host claim can be held on both nodes. Native ack is not exposed (the view and the route agree, so there is no acked → unacked revert). Denying until self is Up was not adopted: it would also deny writes/acks during a single-node cluster's own join (review R6 MINOR-2). The alerts emit is skipped (the Primary peer publishes the single fleet copy). The window closes on the first delivered snapshot.
 
 Under warm/hot redundancy both cluster nodes run `ScriptedAlarmHostActor` and evaluate scripted alarms, keeping each node's address space and engine state warm for instant failover. To avoid duplicate rows on `/alerts` and duplicate historian writes, only the Primary node publishes externally: