Judge the ask and the settle by one say of the builder (issue 1886, merge check hang)

The settle read the say from the builder's bucket while the ask read it through
builderSaysReferences; where they differed (a test's say against a bus with no
bucket) a module was handed back and taken from its key again at every turn,
and the look's loop never ended.

cmd/mesh-controller/builder_says_test.go

@@ -127,7 +127,6 @@ func TestAnOpenWalkWaitingOnAnUnreferencedKeyIsAskedOfBuildAgent(t *testing.T) {
 
 	// Not said: handed back, and the next look asks build-agent.
 	p, byName, keys := walk()
-	keys.notSaid = true
 	theBuilderSays(t, false, nil)
 	asked := askingBuildAgent(t)
 	changed, err := settleKeys(t.Context(), records, keys, p, p.Tiers[0], take)
@@ -154,7 +153,8 @@ func TestAFailedKeyOfABuilderThatDoesNotSayFailsNoWalk(t *testing.T) {
 	askModule(t.Context(), p, "sudo", byName)
 	_ = byName
 	fp := "src2:" + strings.Repeat("f", 64)
-	keys := planKeysOf{notSaid: true, values: map[string]sdkdelivery.Module{"sudo@c0ffee0123456789": {FP2: fp}},
+	theBuilderSays(t, false, nil)
+	keys := planKeysOf{values: map[string]sdkdelivery.Module{"sudo@c0ffee0123456789": {FP2: fp}},
 		keys: map[string]builderkeys.Key{"sudo": {Module: "sudo", Fingerprint: fp, Found: true,
 			Build: sdkdelivery.BuilderBuild{State: sdkdelivery.BuildFailed, Error: "not stored: tools: no reference"}}}}
 	if _, err := settleKeys(t.Context(), recordsOf{}, keys, p, p.Tiers[0], func(string, sdkdelivery.Module, string) {}); err != nil {
@@ -221,3 +221,23 @@ func TestTheAskGuardUsesTheSayTheWalkRead(t *testing.T) {
 		}
 	}
 }
+
+// 1886 merge check hang: the look must judge an ask and a settle by one say. A settle that read the say from another
+// source than the ask (the bus's bucket, against the walk's read) handed a module back, the next ask took it from its key
+// again, and the look's loop never ended: walk_from_keys_integration_test hung.
+func TestTheSettleJudgesByTheSameSayAsTheAsk(t *testing.T) {
+	theBuilderSays(t, true, nil)
+	p, _ := aWalkOfOne("sudo")
+	p.Modules["sudo"] = &inventory.PlanModule{}
+	askModule(t.Context(), p, "sudo", map[string]inventory.Entry{"sudo": {Source: inventory.Source{Repository: "novox/mesh-catalog", Path: "modules/sudo", Ref: "main"}}})
+	fp := "src2:" + strings.Repeat("1", 64)
+	keys := planKeysOf{values: map[string]sdkdelivery.Module{"sudo@c0ffee0123456789": {FP2: fp}},
+		keys: map[string]builderkeys.Key{"sudo": {Module: "sudo", Fingerprint: fp, Found: true,
+			Build: sdkdelivery.BuilderBuild{State: sdkdelivery.BuildBuilding, By: "shanks"}}}}
+	if _, err := settleKeys(t.Context(), recordsOf{}, keys, p, p.Tiers[0], func(string, sdkdelivery.Module, string) {}); err != nil {
+		t.Fatal(err)
+	}
+	if s := p.Modules["sudo"]; !s.Key || s.State != "asked" {
+		t.Fatalf("the settle judged by another say than the ask's: %+v", s)
+	}
+}

cmd/mesh-controller/plan_keys.go

@@ -47,8 +47,6 @@ var buildersOwn = func(module string) bool { return buildAgentsOwn[module] }
 type planKeyReads interface {
 	ModuleAt(ctx context.Context, module, commit string) (sdkdelivery.Module, error)
 	Build(ctx context.Context, module, fp string) (builderkeys.Key, error)
-	// SaysReferences is whether a running builder says it writes references (builderkeys.Reader.SaysReferences).
-	SaysReferences(ctx context.Context) (bool, error)
 }
 
 // builderSayKey carries, on an ask's context, the builder's say the walk read before asking (withBuilderSay).
@@ -135,7 +133,9 @@ func settleKeys(ctx context.Context, inv keyRecords, keys planKeyReads, p *inven
 			changed = true
 		}
 	}
-	says, err := keys.SaysReferences(ctx)
+	// One say for the ask and the settle (builderSaysReferences): two sources that differ hand a module back and take it
+	// from its key again at every turn of the look, which then never ends.
+	says, err := builderSaysReferences(ctx)
 	if err != nil {
 		return changed, fmt.Errorf("whether the builder writes references cannot be read: %w", err)
 	}

cmd/mesh-controller/plan_keys_test.go

@@ -16,12 +16,8 @@ import (
 type planKeysOf struct {
 	values map[string]sdkdelivery.Module // by module + "@" + commit
 	keys   map[string]builderkeys.Key
-	// notSaid is a builder that does not say it writes references (issue 1886); the zero value says it.
-	notSaid bool
 }
 
-func (k planKeysOf) SaysReferences(context.Context) (bool, error) { return !k.notSaid, nil }
-
 func (k planKeysOf) ModuleAt(_ context.Context, module, commit string) (sdkdelivery.Module, error) {
 	if v, ok := k.values[module+"@"+commit]; ok {
 		return v, nil