Bound a state watch's hand-over by its progress, not its whole set, so a large state's newest keys are handed over (issue 1726)

The gitea module's watch of mesh-delivery-checker.owed failed at every attempt
since 03:05 on novox: about 200 owed keys, each a round trip to the bundle,
outlast a 10 s bound for the whole set. The bundle dropped its handler, the
oldest keys were written again every 40 s and the newest, handed over last,
never were: group fix/1937-done-key-blobs's pass never reached mesh/check.
StateWatch now fails only when no current value is handed over within
StateTimeout.

node-tools/internal/bus/state.go

@@ -261,7 +261,12 @@ func (c *Conn) writable(module, name string) (StateIssued, error) {
 
 // StateWatch hands deliver the current value of every key matching the pattern — none that is
 // deleted — and then every change, in order (ADR 0201). It returns once the current values are
-// delivered; deliver is called from one goroutine, one change at a time, and an error from it is said
+// delivered. **StateTimeout bounds the time without progress, not the whole set** (novox/hq issue
+// 1726): each current value is a round trip to the bundle, so a state of a few hundred keys outlasts
+// any fixed bound for all of them; the watch then failed at every attempt, the bundle dropped its
+// handler, and the newest keys, handed over last, were never taken (the checker's owed, whose newest
+// verdicts never reached mesh/check). It fails only when no current value arrives, or one is not
+// taken, within StateTimeout; deliver is called from one goroutine, one change at a time, and an error from it is said
 // and the watch goes on: state is not a queue, and the next change, or the next start, reads it again.
 // The pattern is a key, with `*` for one name and `**` for the rest; empty is every key.
 func (c *Conn) StateWatch(module, name, pattern string, deliver func(StateChange) error) (stop func(), err error) {
@@ -306,6 +311,14 @@ func (c *Conn) StateWatch(module, name, pattern string, deliver func(StateChange
 		})
 	}
 	current := make(chan struct{})
+	// handed says a current value was handed over or passed by: progress, which restarts the bound.
+	handed := make(chan struct{}, 1)
+	progress := func() {
+		select {
+		case handed <- struct{}{}:
+		default:
+		}
+	}
 	go func() {
 		initial := true
 		for e := range w.Updates() {
@@ -326,6 +339,7 @@ func (c *Conn) StateWatch(module, name, pattern string, deliver func(StateChange
 				// A deletion among the current values is a key that is not there: not handed over
 				// (measured, research 024 — the server sends its marker among the initial values).
 				if initial {
+					progress()
 					continue
 				}
 				change.Op = "delete"
@@ -334,17 +348,32 @@ func (c *Conn) StateWatch(module, name, pattern string, deliver func(StateChange
 				c.Logf("[mesh-tools] %s did not take %s %s of %s: %v; its next change, or its next start, reads it again",
 					module, change.Op, change.Key, name, err)
 			}
+			if initial {
+				progress()
+			}
 		}
 		if initial {
 			close(current)
 		}
 	}()
-	select {
-	case <-current:
-		return stop, nil
-	case <-time.After(StateTimeout):
-		stop()
-		return nil, fmt.Errorf("the current values of %s did not arrive in %s", name, StateTimeout)
+	bound := time.NewTimer(StateTimeout)
+	defer bound.Stop()
+	for {
+		select {
+		case <-current:
+			return stop, nil
+		case <-handed:
+			if !bound.Stop() {
+				select {
+				case <-bound.C:
+				default:
+				}
+			}
+			bound.Reset(StateTimeout)
+		case <-bound.C:
+			stop()
+			return nil, fmt.Errorf("the current values of %s did not arrive in %s: none was handed over in that time", name, StateTimeout)
+		}
 	}
 }