Per-cluster mesh Phase 6 (Task 5). A node carrying a cluster-{ClusterId}
role (RoleParser.IsClusterRole) is in the split topology, where the
Phase 2/3/5 DPS dark-switch branches deliver nothing across the mesh
boundary. SplitTopologyTransportValidator fails host start unless such a
node uses the mesh-crossing transports: MeshTransport:Mode=ClusterClient
always; Telemetry:Mode=Grpc if it has the driver role; TelemetryDial:Mode
=Grpc if it has the admin role. It is a no-op for any node with no
cluster-role (legacy / single-mesh / test). Roles + the three modes are
cross-read from IConfiguration, mirroring ConfigSourceOptionsValidator.
Registered via AddValidatedOptions on MeshTransportOptions with
ValidateOnStart, alongside the sibling validators.
Claude-Session: https://claude.ai/code/session_01GASWkNEi68FSCtvr6rLoEW
Joseph Doherty
a886d5e6e0