The node-engine serves manifest-reads and says manifest-reads-changed once per link (ADR 0618 §3, §4, issue 774)

Claude-Session: https://claude.ai/code/session_01JG73KG7AfSdh6FP8VrBqCn

internal/link/session.go

@@ -87,6 +87,12 @@ type Session struct {
 	// saying is held while a facts event is noted, so the haves are written in the order the facts are made.
 	saying sync.Mutex
 
+	// reads says whether the engine has said its manifest reads on a link before (novox/hq ADR 0618 §4).
+	reads struct {
+		sync.Mutex
+		linked bool
+	}
+
 	// haves is what this node-engine writes beside its facts (novox/hq ADR 0429 §4, issue 1132).
 	haves haveState
 	// healthWritten is this node's health report as last written or read (WriteNodeHealth): the health loop alone
@@ -383,6 +389,32 @@ func (q *Session) RouterRecord(key string) (*stdio.StateEntry, error) {
 	return asking.RouterRecord(key)
 }
 
+// StatedReads is what this engine states it reads of a manifest and when it computed them, which is its start (the
+// node seat's verb manifest-reads, novox/hq ADR 0618 §3): the record is written only when it differs, so its put says
+// nothing of when an unchanged statement was made.
+func (q *Session) StatedReads() ([]string, time.Time) { return manifestReads(), readsStatedAt }
+
+// SayReads says the node seat's event manifest-reads-changed once for the link just opened (novox/hq ADR 0618 §4):
+// why "started" on the engine's first link and "returned" on every link after it, so a reader asks the verb again once
+// per connection and never once per pass.
+func (q *Session) SayReads() {
+	q.reads.Lock()
+	why := delivery.ReadsStarted
+	if q.reads.linked {
+		why = delivery.ReadsReturned
+	}
+	q.reads.linked = true
+	q.reads.Unlock()
+	raw, err := delivery.EncodeManifestReadsChanged(delivery.ManifestReadsChanged{Node: q.Membership.Node,
+		ManifestReads: manifestReads(), At: time.Now().UTC(), Why: why})
+	if err != nil {
+		q.init()
+		q.Say("cannot say the node seat's manifest-reads-changed: " + err.Error())
+		return
+	}
+	q.SayEngine("manifest-reads-changed", json.RawMessage(raw))
+}
+
 // SayEngine says one of the node seat's events over the link open now; with none open it is not said.
 func (q *Session) SayEngine(event string, body any) {
 	q.init()