Pause before a declined ask is put again with a context's bound, not a timer (ADR 0437 §8, issue 1578)

The builder's manifest test refuses time.After. The previous commit's pause used it.

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

modules/mesh-delivery-builder/internal/build/askagain.go

@@ -326,10 +326,12 @@ func (b *Builder) answer(ctx context.Context, l *lane, ask delivery.StepAsk, ask
 			if bound := b.declineBound(); now.Sub(firstDecline) > bound {
 				return step, ask, fmt.Errorf("the ask %s of %s was declined for %s and no build node took it: %s", ask.ID, l.module, bound.Round(time.Second), declinedWords(declines))
 			}
-			select {
-			case <-ctx.Done():
+			// The pause is a context's bound, not a timer (ADR 0437 §8).
+			pause, stop := context.WithTimeout(ctx, b.declinePause())
+			<-pause.Done()
+			stop()
+			if ctx.Err() != nil {
 				return step, ask, ctx.Err()
-			case <-time.After(b.declinePause()):
 			}
 			old := ask.ID
 			ask.ID, ask.At = buildstep.NewID(), time.Now()