Say a build handed out again restarted, in its log, the queue and the check's verdict

A build agent replaced mid-build leaves its ask to be handed out again, and
the second run looked like a first: the queue and the pull request showed
nothing of the 5-8 minutes lost (novox/hq issue 594).

cmd/mesh-controller/queue.go

@@ -141,6 +141,9 @@ type queuedAnswer struct {
 	// Position is its place among the waiting, 1 being handed out next; 0 for an ask not waiting.
 	Position int    `json:"position,omitempty"`
 	Seq      uint64 `json:"seq"`
+	// Delivery is the how-manyth time an ask in flight was handed out; more than 1 is a restart
+	// (novox/hq issue 594).
+	Delivery int `json:"delivery,omitempty"`
 }
 
 // aCommitRef is a ref that names a commit by its full hash (SHA-1 or SHA-256).
@@ -164,7 +167,7 @@ func queueAnswerOf(q link.Queue, now time.Time) queueAnswer {
 		}
 		return queuedAnswer{ID: a.ID, State: a.State, Kind: kind, Repository: link.WithoutPassword(a.Repository), Path: a.Path,
 			Ref: a.Ref, Commit: commit, Machine: a.On, WasOn: a.Was, AskedAt: a.AskedAt, Since: since,
-			Position: position, Seq: a.Seq}
+			Position: position, Seq: a.Seq, Delivery: a.Delivery}
 	}
 	for _, a := range running {
 		out.Asks = append(out.Asks, one(a, 0))
@@ -207,6 +210,10 @@ func queueText(q link.Queue, now time.Time) string {
 			switch {
 			case a.On != "":
 				where = fmt.Sprintf("on %s for %s", a.On, now.Sub(a.Started).Round(time.Second))
+				// Started again after an earlier taker left it (novox/hq issue 594).
+				if a.Delivery > 1 {
+					where += fmt.Sprintf(", restarted (handed out %d times)", a.Delivery)
+				}
 			case a.Was != "":
 				where = fmt.Sprintf("handed back by %s, to be handed out again", a.Was)
 			}