test: make the ecosystem fault suite fail when the feature is deleted

Several assertions passed against code with the behaviour removed. The
independent-outage test shared no state to begin with, the capability
fixture used to prove read-only filtering was already mutating, and
route-level faults were simulated with a separate fake instead of the
shared one. The harness now takes per-route faults and a ticking clock,
so durations are measurable and one dead endpoint can be shown not to
mute a whole service. New cases cover a resolved reference with no
entity, a rejected credential, a malformed Praxis body, foreign items
in a scoped response, named truncation, traces staying out of facts,
and enrichment making progress while its oldest batch is backed off.

Found in review of #82.

cmd/mavend/entityrefs_test.go

@@ -28,7 +28,7 @@ func entityAttentionDec(subject string) router.Decision {
 func TestEntityAttention_ScopesPraxisByCanonicalID(t *testing.T) {
 	ctx := context.Background()
 	nexus := newFakeNexus(t, fixtureNexusResolved("ent_muzick", "Muzick indexer", "service"))
-	praxis := newFakePraxis(t, fixturePraxisAttentionItems(
+	praxis := newFakePraxis(t, fixturePraxisAttentionScoped("ent_muzick",
 		map[string]any{"id": "item_1", "title": "indexer queue is backing up", "importance": 3.0},
 	))
 	h := ecoHandler(t, nexus, praxis, nil)
@@ -76,6 +76,76 @@ func TestEntityAttention_FoldsInLocalFactsForSameEntity(t *testing.T) {
 	}
 }
 
+// TestEntityAttention_UnscopedPraxisResponseIsRefused: a Praxis old enough to
+// ignore the entity_id parameter answers the scoped question with the whole
+// unscoped list. Relabelling those items "по «X»" is the same fabrication the
+// canonical ref exists to prevent, arriving through a different door.
+func TestEntityAttention_UnscopedPraxisResponseIsRefused(t *testing.T) {
+	ctx := context.Background()
+	nexus := newFakeNexus(t, fixtureNexusResolved("ent_muzick", "Muzick indexer", "service"))
+	praxis := newFakePraxis(t, fixturePraxisAttentionItems(
+		map[string]any{"id": "item_1", "title": "disk almost full", "importance": 3.0},
+	))
+	h := ecoHandler(t, nexus, praxis, nil)
+
+	reply := h.handlePraxisAct(ctx, entityAttentionDec("muzick indexer"))
+	if strings.Contains(reply, "disk almost full") {
+		t.Fatalf("an unscoped response must not be read back as entity-scoped, got %q", reply)
+	}
+	if reply == "" {
+		t.Fatal("refusing the answer must still say something")
+	}
+	if praxis.Count("POST", "/api/v1/tools/surface") != 0 {
+		t.Error("items that were never spoken must not be surfaced")
+	}
+}
+
+// TestEntityAttention_ForeignItemsAreDropped: items tagged with another entity
+// are dropped rather than spoken under this entity's name.
+func TestEntityAttention_ForeignItemsAreDropped(t *testing.T) {
+	ctx := context.Background()
+	nexus := newFakeNexus(t, fixtureNexusResolved("ent_muzick", "Muzick indexer", "service"))
+	mixed := []map[string]any{
+		{"id": "item_1", "title": "indexer queue is backing up", "importance": 3.0, "entity_id": "ent_muzick"},
+		{"id": "item_2", "title": "the kettle is descaling", "importance": 1.0, "entity_id": "ent_kettle"},
+	}
+	praxis := newFakePraxis(t, mustJSON(mixed))
+	h := ecoHandler(t, nexus, praxis, nil)
+
+	reply := h.handlePraxisAct(ctx, entityAttentionDec("muzick indexer"))
+	if !strings.Contains(reply, "indexer queue is backing up") {
+		t.Fatalf("the matching item must be spoken, got %q", reply)
+	}
+	if strings.Contains(reply, "kettle") {
+		t.Fatalf("another entity's item must not be spoken here, got %q", reply)
+	}
+}
+
+// TestEntityAttention_TruncationIsNamed: reading three of many remembered
+// facts must not be presented as everything she knows.
+func TestEntityAttention_TruncationIsNamed(t *testing.T) {
+	ctx := context.Background()
+	nexus := newFakeNexus(t, fixtureNexusResolved("ent_espresso", "the espresso machine", "device"))
+	praxis := newFakePraxis(t, fixturePraxisAttentionItems())
+	h := ecoHandler(t, nexus, praxis, nil)
+
+	for i := 0; i < 5; i++ {
+		id, err := h.dataStore.WriteFactAboutSubject(ctx, time.Now(), store.KindEnv,
+			"note", "the espresso machine", "факт "+string(rune('а'+i)), "infer:pref", 0.8, sql.NullInt64{})
+		if err != nil {
+			t.Fatalf("WriteFactAboutSubject: %v", err)
+		}
+		if err := h.dataStore.ResolveFactEntity(ctx, id, "ent_espresso", store.ResolutionResolved); err != nil {
+			t.Fatalf("ResolveFactEntity: %v", err)
+		}
+	}
+
+	reply := h.handlePraxisAct(ctx, entityAttentionDec("the espresso machine"))
+	if !strings.Contains(reply, "и это не всё") {
+		t.Fatalf("a truncated recall must say it is truncated, got %q", reply)
+	}
+}
+
 // TestEntityAttention_AmbiguousAsksInsteadOfGuessing.
 func TestEntityAttention_AmbiguousAsksInsteadOfGuessing(t *testing.T) {
 	ctx := context.Background()
@@ -145,7 +215,7 @@ func TestEntityAttention_WithoutNexusSaysSo(t *testing.T) {
 
 	reply := h.handlePraxisAct(ctx, entityAttentionDec("muzick indexer"))
 	if strings.Contains(reply, "disk almost full") {
-		t.Fatalf("unscoped items must not be passed off as entity-scoped, got %q", reply)
+		t.Fatalf("without nexus, items must not be passed off as entity-scoped, got %q", reply)
 	}
 	if praxis.Count("GET", "/api/v1/tools/attention") != 0 {
 		t.Fatal("no canonical ref means no scoped query at all")
@@ -211,3 +281,78 @@ func TestEnrichmentBackoff_GrowsAndIsCapped(t *testing.T) {
 		t.Fatalf("backoff must cap at an hour, got %v", enrichmentBackoff(50))
 	}
 }
+
+// TestEnrichment_BackedOffFactsDoNotStallTheQueue: the pending queue is ordered
+// by id, so the oldest facts are pulled first whether or not they are eligible.
+// A batch of facts in backoff at the head must not hold every slot and stop
+// enrichment for everything younger.
+func TestEnrichment_BackedOffFactsDoNotStallTheQueue(t *testing.T) {
+	ctx := context.Background()
+	st := newTestStore(t)
+	total := 5
+	for i := 0; i < total; i++ {
+		if _, err := st.WriteFactAboutSubject(ctx, time.Now(), store.KindEnv, "likes",
+			"subject-"+string(rune('a'+i)), `"true"`, "infer:pref", 0.8, sql.NullInt64{}); err != nil {
+			t.Fatalf("WriteFactAboutSubject: %v", err)
+		}
+	}
+
+	nexus := newFakeNexus(t, fixtureNexusResolved("ent_x", "X", "service"))
+	clock := newFakeClock(time.Date(2026, 8, 1, 3, 0, 0, 0, time.UTC))
+	w := newFactEnrichmentWorker(st, stubEcosystem(nexus.URL, ""), time.Hour)
+	w.now = clock.Now
+	// A batch smaller than the queue, so with no scan the last fact never
+	// reaches the head while the first ones are backed off.
+	w.batch = total - 1
+
+	nexus.SetFault(503)
+	w.tick(ctx)
+	if got := nexus.Count("POST", "/api/v1/resolve"); got != total-1 {
+		t.Fatalf("expected the first batch attempted, got %d calls", got)
+	}
+
+	// Second tick with Nexus healthy: the backed-off head must be skipped and
+	// the fact behind it resolved, not the same batch pulled and dropped.
+	nexus.SetFault(0)
+	w.tick(ctx)
+	facts, err := st.FactsByEntity(ctx, "ent_x", 10)
+	if err != nil {
+		t.Fatalf("FactsByEntity: %v", err)
+	}
+	if len(facts) == 0 {
+		t.Fatal("a due fact behind a backed-off batch must still be resolved")
+	}
+}
+
+// TestEnrichment_StoreWriteFailureBacksOffToo: the one failure mode where the
+// resolve worked and the write did not must be paced like any other, not
+// retried at full rate forever.
+func TestEnrichment_StoreWriteFailureBacksOffToo(t *testing.T) {
+	ctx := context.Background()
+	nexus := newFakeNexus(t, fixtureNexusResolved("ent_espresso", "the espresso machine", "device"))
+	st := newTestStore(t)
+	if _, err := st.WriteFactAboutSubject(ctx, time.Now(), store.KindEnv, "likes",
+		"the espresso machine", `"true"`, "infer:pref", 0.8, sql.NullInt64{}); err != nil {
+		t.Fatalf("WriteFactAboutSubject: %v", err)
+	}
+	pending, err := st.PendingFactResolutions(ctx, 10)
+	if err != nil || len(pending) != 1 {
+		t.Fatalf("setup: pending = %+v, %v", pending, err)
+	}
+
+	clock := newFakeClock(time.Date(2026, 8, 1, 3, 0, 0, 0, time.UTC))
+	w := newFactEnrichmentWorker(st, stubEcosystem(nexus.URL, ""), time.Hour)
+	w.now = clock.Now
+
+	// Closing the store makes the resolution write fail while the Nexus call
+	// still succeeds — the split this path gets wrong.
+	if err := st.Close(); err != nil {
+		t.Fatalf("close store: %v", err)
+	}
+	if w.resolveOne(ctx, pending[0]) {
+		t.Fatal("a failed store write must not report success")
+	}
+	if w.due(pending[0].ID) {
+		t.Fatal("a failed store write must back the fact off like a failed resolve")
+	}
+}