Assigner: keep the held record of a fingerprint whose asks went stale (issue 1906)

The held record is the memory that a fingerprint failed (ADR 0408 section 4); a revert returns the
trunk to exactly it, and without the key rule 3 would move the canary onto the failed build with
nothing asked. A stale hold ask now clears only the condition (raised again on a revisit), and the
hold is asked again under a new asking. Also read the single want key for a record ask.

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/pass.go

@@ -459,7 +459,11 @@ func (p *passer) fingerprintsOf(node, module, trunkFP string) []string {
 		}
 	}
 	add(trunkFP)
-	add(p.w.wantsOf()[module][node].FP)
+	if key, err := delivery.WantKey(node, module); err == nil {
+		if w, err := delivery.DecodeWant(p.w.value(delivery.AssignerWantsBucket, key)); err == nil {
+			add(w.FP)
+		}
+	}
 	if key, err := delivery.HaveKey(node, module); err == nil {
 		if h, err := delivery.DecodeHave(p.w.value(delivery.HaveBucket, key)); err == nil {
 			add(h.FP)
@@ -479,13 +483,12 @@ func (p *passer) staleAsks(ctx context.Context, trunk map[string]delivery.Module
 		if p.staleAsk(key, trunk) {
 			p.logf("the ask %s is about a fingerprint or composition the trunk has left behind and is taken away", key)
 			p.remove(ctx, delivery.AssignerAsksBucket, key)
-			// A hold or restore ask of a fingerprint the trunk left goes with the hold itself: its held record, and its condition,
-			// which would else ask for an answer that can no longer be given.
+			// The held record stays: it is the memory that this fingerprint failed (ADR 0408 §4), and a revert returns the trunk to
+			// exactly it. Only the condition, which would else ask for an answer that can no longer be given, is cleared, and it is
+			// raised again if the trunk returns to the fingerprint.
 			if k, err := delivery.ParseAnyAskKey(key); err == nil && (k.Kind == delivery.AskKindHold || k.Kind == delivery.AskKindRestore) {
-				if held, err := delivery.HeldKey(k.Module, k.FP); err == nil {
-					p.remove(ctx, delivery.AssignerWantsBucket, held)
-				}
 				p.clearHeld(k.Module, k.FP)
+				delete(p.said, assign.HeldCondition(k.Module, k.FP, "", "", false, false).Key+".raised")
 			}
 		}
 	}

modules/mesh-delivery-assigner/cmd/mesh-delivery-assigner/pass_test.go

@@ -574,6 +574,7 @@ func TestAsksOfAFingerprintTheTrunkLeftBehindAreTakenAway(t *testing.T) {
 			heldOld, _ := delivery.HeldKey("web", fpOld)
 			wantsKV.values[heldOld] = []byte("x")
 			p.w.put(delivery.AssignerWantsBucket, heldOld, []byte("x"))
+			firstAsk, _ := delivery.DecodeAssignerAsk(holdOld, asksKV.values[holdOld])
 			p.staleAsks(context.Background(), c.trunk)
 			// the held record and condition of a fingerprint whose hold ask went are taken away with it
 			heldOld, _ = delivery.HeldKey("web", fpOld)
@@ -581,8 +582,8 @@ func TestAsksOfAFingerprintTheTrunkLeftBehindAreTakenAway(t *testing.T) {
 			cleared := slices.ContainsFunc(said, func(c asks.Condition) bool {
 				return c.Key == assign.HeldCondition("web", fpOld, "", "", false, false).Key && c.State == asks.StateCleared
 			})
-			if gone := slices.Contains(c.gone, holdOld); heldThere == gone || cleared != gone {
-				t.Errorf("hold ask of the old fingerprint gone = %v, but its held record left = %v and its condition cleared = %v", gone, heldThere, cleared)
+			if gone := slices.Contains(c.gone, holdOld); !heldThere || cleared != gone {
+				t.Errorf("hold ask of the old fingerprint gone = %v: its held record stays = %v (must), its condition cleared = %v", gone, heldThere, cleared)
 			}
 			for _, key := range all {
 				_, there := asksKV.values[key]
@@ -591,6 +592,17 @@ func TestAsksOfAFingerprintTheTrunkLeftBehindAreTakenAway(t *testing.T) {
 					t.Errorf("%s: left in the bucket = %v, want %v", key, there, want)
 				}
 			}
+			if slices.Contains(c.gone, holdOld) {
+				// the trunk returns to the fingerprint (a revert): the held record still holds it, and it is asked and said again
+				p.now = func() time.Time { return time.Now().Add(time.Hour) }
+				p.holdAsk(context.Background(), "web", fpOld, nil)
+				p.heldCondition(context.Background(), "web", fpOld, nil, false)
+				again, err := delivery.DecodeAssignerAsk(holdOld, asksKV.values[holdOld])
+				raised := slices.ContainsFunc(said, func(c asks.Condition) bool { return c.State == asks.StateRaised })
+				if err != nil || again.Ask.ID == firstAsk.Ask.ID || !raised {
+					t.Errorf("the trunk returned to the held fingerprint: ask %q (first %q, %v), condition raised again = %v", again.Ask.ID, firstAsk.Ask.ID, err, raised)
+				}
+			}
 		})
 	}
 
@@ -646,6 +658,9 @@ func TestARecordAskOfAHeldBackNodeSurvivesPassesAndItsYesMovesTheWant(t *testing
 		t.Fatal(cerr)
 	}
 	put(delivery.ControllerComposedBucket, ckey, cd)
+	tkey, _ := delivery.ComposedKey("g14", "web", fpTest) // the trunk's own composition, another digest than the revised one
+	tcd, _ := delivery.EncodeComposedDigest(delivery.ComposedDigest{Digest: "sha256:" + strings.Repeat("f", 64), Judgement: delivery.JudgedUnchanged})
+	put(delivery.ControllerComposedBucket, tkey, tcd)
 	akey, _ := delivery.RecordAskKey("g14", "web", revised)
 	for i := 0; i < 2; i++ {
 		p.wants(context.Background())