Joseph Doherty 84fe88fadb Phase 6.3 Stream A — RedundancyTopology + ClusterTopologyLoader + RedundancyCoordinator ...

Lands the data path that feeds the Phase 6.3 ServiceLevelCalculator shipped in
PR #89. OPC UA node wiring (ServiceLevel variable + ServerUriArray +
RedundancySupport) still deferred to task #147; peer-probe loops (Stream B.1/B.2
runtime layer beyond the calculator logic) deferred.

Server.Redundancy additions:
- RedundancyTopology record — immutable snapshot (ClusterId, SelfNodeId,
  SelfRole, Mode, Peers[], SelfApplicationUri). ServerUriArray() emits the
  OPC UA Part 4 §6.6.2.2 shape (self first, peers lexicographically by
  NodeId). RedundancyPeer record with per-peer Host/OpcUaPort/DashboardPort/
  ApplicationUri so the follow-up peer-probe loops know where to probe.
- ClusterTopologyLoader — pure fn from ServerCluster + ClusterNode[] to
  RedundancyTopology. Enforces Phase 6.3 Stream A.1 invariants:
    * At least one node per cluster.
    * At most 2 nodes (decision #83, v2.0 cap).
    * Every node belongs to the target cluster.
    * Unique ApplicationUri across the cluster (OPC UA Part 4 trust pin,
      decision #86).
    * At most 1 Primary per cluster in Warm/Hot modes (decision #84).
    * Self NodeId must be a member of the cluster.
  Violations throw InvalidTopologyException with a decision-ID-tagged message
  so operators know which invariant + what to fix.
- RedundancyCoordinator singleton — holds the current topology + IsTopologyValid
  flag. InitializeAsync throws on invariant violation (startup fails fast).
  RefreshAsync logs + flips IsTopologyValid=false (runtime won't tear down a
  running server; ServiceLevelCalculator falls to InvalidTopology band = 2
  which surfaces the problem to clients without crashing). CAS-style swap
  via Volatile.Write so readers always see a coherent snapshot.

Tests (10 new ClusterTopologyLoaderTests):
- Single-node standalone loads + empty peer list.
- Two-node cluster loads self + peer.
- ServerUriArray puts self first + peers sort lexicographically.
- Empty-nodes throws.
- Self-not-in-cluster throws.
- Three-node cluster rejected with decision #83 message.
- Duplicate ApplicationUri rejected with decision #86 shape reference.
- Two Primaries in Warm mode rejected (decision #84 + runtime-band reference).
- Cross-cluster node rejected.
- None-mode allows any role mix (standalone clusters don't enforce Primary count).

Full solution dotnet test: 1178 passing (was 1168, +10). Pre-existing
Client.CLI Subscribe flake unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

2026-04-19 11:24:14 -04:00

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