Node-engine: the placement's bucket and read names come from the assigner client (ADR 0634 §4; issue 1966)

Claude-Session: https://claude.ai/code/session_01NcbgfFSnn24M3GcqttoU7i

internal/compose/frombus/states.go

@@ -28,7 +28,7 @@ import (
 const (
 	// The holders' names are kept here, in the engine's own code, as the names of the states a manifest's reads use
 	// (ADR 0634 §1, finding F4); a seat's contract names a state locally, not the module that holds it.
-	PlacementRead = "mesh-delivery-assigner.placement"
+	PlacementRead = meshmoduleassignerclient.PlacementRead
 	ModulesRead   = "mesh-delivery-indexer.modules"
 	ManifestsRead = "mesh-delivery-indexer.manifests"
 	BuildsRead    = "mesh-delivery-builder.builds"