J2: a state read carries the time the bus wrote the value, as at (stdio.StateEntry.At)

Claude-Session: https://claude.ai/code/session_01JG73KJNrH5EgFXMKKYSrig

node-tools/internal/bus/state.go

@@ -39,6 +39,8 @@ type StateEntry struct {
 	Key      string          `json:"key"`
 	Value    json.RawMessage `json:"value"`
 	Revision uint64          `json:"revision"`
+	// At is when the bus wrote this value (the entry's created time), as stdio.StateEntry.At reads it.
+	At time.Time `json:"at,omitzero"`
 }
 
 // StateChange is one change a watch delivers: a key put, deleted, or expired (its own time to live, or the
@@ -134,7 +136,7 @@ func (c *Conn) StateGet(module, name, key string) (*StateEntry, error) {
 	if err != nil {
 		return nil, err
 	}
-	return &StateEntry{Key: e.Key(), Value: valueOf(e.Value()), Revision: e.Revision()}, nil
+	return &StateEntry{Key: e.Key(), Value: valueOf(e.Value()), Revision: e.Revision(), At: e.Created().UTC()}, nil
 }
 
 // StateKept is one value a bucket still keeps for a key: a put, or a delete (a purge reads as one).