The mesh says what it applied, and the replay has an address it may use

The pipeline was observable from a merge to an artifact and went dark where it touched a machine: a
node's report is control traffic only the control plane reads, so nothing said which version a
machine runs, or that it refused to (novox/hq ADR 0134). The control plane now states both under the
seat it holds — a role's events belong to the role and keep their address when the holder is
replaced — and only when the report is news, because a machine reconciles every minute and a fact per
report would be a fact per minute per machine.

Whether a report is news is the store's answer: it holds the previous one, so the listener returns it
and the server states the fact. That also gives the catch-up replay a subject the controller may
publish: it was published as a module's event from a module called "control-plane", which does not
exist, so the controller's own account refused it and every catalogue that asked what it missed was
answered with nothing.

internal/link/bus.go

@@ -30,6 +30,11 @@ type Bus interface {
 	// (design 29 §4, the *state* shape).
 	PublishDeclaration(ctx context.Context, node string, body []byte) error
 
+	// PublishSeatEvent states a fact under a role's own name, for the holder of that role. A
+	// module's event is addressed to the module; a role's is addressed to the role, so it keeps
+	// meaning when the holder changes (novox/hq ADR 0121, ADR 0129).
+	PublishSeatEvent(ctx context.Context, seat, event string, body []byte) error
+
 	// AskTool sends one question to a module's tool and awaits one answer. A tool nobody serves
 	// must say so **at once** rather than after the whole wait: the difference between "that
 	// module is down" and "that tool is slow" is the first thing a person asking wants.
@@ -81,6 +86,13 @@ func EventSubject(source, key string) string {
 	return "mesh.mod." + source + ".event." + key
 }
 
+// SeatEventSubject is where a role's own event lands. Derived from the role, never from its holder:
+// a fact about the build machine or about the control plane keeps its address when the module holding
+// that role is replaced (novox/hq ADR 0121, ADR 0129).
+func SeatEventSubject(seat, event string) string {
+	return "mesh.seat." + seat + ".event." + event
+}
+
 // DeclareSubject is where one node's declaration lands. Last-per-subject on the NODES stream, so
 // a node that was away gets exactly the current one and a replayed older one is refused by
 // sequence — the wire-level answer to novox/hq issue 107.
@@ -112,6 +124,27 @@ func (b OverNATS) PublishEvent(ctx context.Context, key, source, node string, bo
 	return nil
 }
 
+// PublishSeatEvent states a role's own fact. Same envelope as a module's event and a different
+// address: the source header is the role, because that is what the fact is about.
+func (b OverNATS) PublishSeatEvent(ctx context.Context, seat, event string, body []byte) error {
+	id, err := eventID()
+	if err != nil {
+		return err
+	}
+	h := nats.Header{}
+	h.Set("x-event-id", id)
+	h.Set("x-source", seat)
+	_, err = b.JS.PublishMsg(&nats.Msg{
+		Subject: SeatEventSubject(seat, event),
+		Header:  h,
+		Data:    body,
+	}, nats.MsgId(id), nats.Context(ctx))
+	if err != nil {
+		return fmt.Errorf("stating %s of the %s seat: %w", event, seat, err)
+	}
+	return nil
+}
+
 func (b OverNATS) PublishDeclaration(ctx context.Context, node string, body []byte) error {
 	_, err := b.JS.Publish(DeclareSubject(node), body, nats.Context(ctx))
 	if err != nil {