Let the mesh's resolver seat have several holders on record

musl takes the first reply from any listed nameserver, so a public fallback
beside the mesh's resolver answered NXDOMAIN for mesh names in every Alpine
container (hq ADR 0223). The fix is two mesh resolvers and no public one, which
needs mesh-dns-resolver held on two machines: a seat can now be replicated,
each holder recorded by 'seat <name> --add', checkClaims accepts every holder
on record and still refuses a second holder of any other mesh seat, a holder
answers its own requirement, and a roster fact gives each replicated seat's
holders, this machine first, so resolv-conf can list them. Migration 0062 keys
a holding by seat and assignment.

internal/catalogue/resolve.go

@@ -767,16 +767,27 @@ func checkClaims(modules []Manifest, node Node, elsewhere []Held, holdings []Hel
 	var problems []string
 	var held []Held
 
-	// onRecord is the recorded holder of a seat, if a handover ever named one.
-	onRecord := func(claim, scope string) (Held, bool) {
+	// onRecord is every recorded holder of a seat, if a handover ever named one: one for most seats,
+	// and as many as were added for a replicated one (novox/hq ADR 0223).
+	onRecord := func(claim, scope string) []Held {
+		var out []Held
 		for _, h := range holdings {
 			hs, ok := SeatNamed(h.Claim)
 			cs, cok := SeatNamed(claim)
 			if ok && cok && hs.Name == cs.Name && h.Scope == scope {
-				return h, true
+				out = append(out, h)
 			}
 		}
-		return Held{}, false
+		return out
+	}
+	// recordedHere says this node's module is one of a seat's holders on record.
+	recordedHere := func(claim, scope, module string) bool {
+		for _, rec := range onRecord(claim, scope) {
+			if rec.Node == node.Name && rec.Module == module {
+				return true
+			}
+		}
+		return false
 	}
 
 	byScope := map[string]map[string]string{} // scope → claim → module
@@ -787,8 +798,18 @@ func checkClaims(modules []Manifest, node Node, elsewhere []Held, holdings []Hel
 			// the seat but is not the one on record is eligible, and that is all: it is not a second
 			// holder, so it is not refused, and it does not hold (novox/hq ADR 0131). This is what
 			// lets the next holder stand beside the current one until the seat is handed over.
-			if rec, recorded := onRecord(c.Name, scope); recorded {
-				if rec.Node != node.Name || rec.Module != m.Module {
+			if recs := onRecord(c.Name, scope); len(recs) > 0 {
+				// **A seat held once is on record once** (novox/hq ADR 0223). Only a replicated seat
+				// may have several holders on record; several for any other seat is a store that
+				// disagrees with the mesh's definition of the role, and it is refused, named, rather
+				// than letting two machines answer for what the mesh has one of.
+				if s, known := SeatNamed(c.Name); known && !s.Replicated && len(recs) > 1 {
+					problems = append(problems, fmt.Sprintf(
+						"%q is on record as held by %d assignments, and it is held once per %s — "+
+							"`seat %s --to <node>/<module>` records one", c.Name, len(recs), scope, c.Name))
+					continue
+				}
+				if !recordedHere(c.Name, scope, m.Module) {
 					continue
 				}
 			}
@@ -815,6 +836,12 @@ func checkClaims(modules []Manifest, node Node, elsewhere []Held, holdings []Hel
 			}
 			switch h.Scope {
 			case ScopeMesh:
+				// **A holder on record is never a second claimant** (novox/hq ADR 0223). Records are
+				// the mesh's settled answer: one for most seats, several only for a replicated seat,
+				// each added by an act. Two holders here are two records, and both hold.
+				if recordedHere(h.Claim, h.Scope, h.Module) {
+					continue
+				}
 				// Both claim and nobody is on record, or this refusal could not have happened.
 				// The remedy is the handover that records the holder (novox/hq ADR 0131,
 				// 04-ISSUES/170), so it is named here rather than left to be found.
@@ -1156,6 +1183,18 @@ func answeredElsewhere(want string, node Node, world World, brokered map[string]
 	if c, pinned := world.Pinned[want]; pinned {
 		return c.Node != node.Name
 	}
+	// **A machine holding the seat answers itself** (novox/hq ADR 0223). With a replicated seat
+	// another machine holds it too, and the first holder in the providers' order may be that one; a
+	// holder is still where this machine's own requirement is answered, so its resolver file lists
+	// itself first.
+	if seat, delivered := SeatDelivering(want); delivered {
+		for _, h := range append(append([]Held(nil), world.Holdings...), world.Held...) {
+			if hs, ok := SeatNamed(h.Claim); ok && hs.Name == seat.Name && h.Scope == seat.Scope &&
+				h.Node == node.Name {
+				return false
+			}
+		}
+	}
 	holder, held := HolderAmong(want, world.Offered[want], world.Held)
 	return held && holder.Node != node.Name
 }