recalleval: a filler id a case reuses is refused at load (V-386)

Every case is scored over its own notes plus the whole filler set, and the
two stores disagree about a repeated id: sqlite upserts on it, the in-memory
store appends. So one collision makes a case score differently on the two
backends, and it reads as an embedder or gate difference — the one thing this
harness exists to measure. It was dodged by hand during #373 by renaming two
ids.

The check sits in Load rather than in TestLoadFixture, so it covers every
caller of the fixture and not only the one that remembers to look.

internal/memory/recalleval/recalleval.go

@@ -90,9 +90,44 @@ func Load() (Fixture, error) {
 	if len(f.Cases) == 0 {
 		return Fixture{}, fmt.Errorf("fixture has no cases")
 	}
+	if err := checkIDs(f); err != nil {
+		return Fixture{}, err
+	}
 	return f, nil
 }
 
+// checkIDs refuses a fixture where a case note and a filler note share an id.
+//
+// Every case is scored over its own notes plus the whole filler set, and the
+// two stores disagree about what a repeated id means: the sqlite store upserts
+// on it, the in-memory store appends. So one collision makes a case score
+// differently on the two backends, and it reads as an embedder or gate
+// difference, which is the one thing this harness exists to measure (Vikunja
+// #386). It was dodged once by hand during #373 by renaming two ids.
+//
+// Checked in Load rather than in the test, so every caller of the fixture is
+// covered and not only the one that remembers to look.
+func checkIDs(f Fixture) error {
+	filler := make(map[string]bool, len(f.Filler))
+	for _, n := range f.Filler {
+		if n.ID == "" {
+			return fmt.Errorf("filler note with an empty id")
+		}
+		if filler[n.ID] {
+			return fmt.Errorf("duplicate filler note id %q", n.ID)
+		}
+		filler[n.ID] = true
+	}
+	for _, c := range f.Cases {
+		for _, n := range c.Notes {
+			if filler[n.ID] {
+				return fmt.Errorf("case %s: note id %q collides with a filler note", c.ID, n.ID)
+			}
+		}
+	}
+	return nil
+}
+
 // NewStore builds an empty store for one case, plus a function to release it.
 // A factory rather than a store because every case needs a clean index — notes
 // from case A must not be visible to case B's query.

internal/memory/recalleval/recalleval_test.go

@@ -337,3 +337,28 @@ func marginSweep(t *testing.T, emb router.Embedder, f Fixture) string {
 	}
 	return b.String()
 }
+
+// TestFillerIDCollisionIsRefused — the guard that keeps a fixture edit from
+// looking like a backend difference (Vikunja #386).
+func TestFillerIDCollisionIsRefused(t *testing.T) {
+	f := Fixture{
+		SchemaVersion: SchemaVersion,
+		Cases:         []Case{{ID: "ru-001", Notes: []StoredNote{{ID: "f1", Text: "..."}}}},
+		Filler:        []StoredNote{{ID: "f1", Text: "..."}},
+	}
+	if err := checkIDs(f); err == nil {
+		t.Fatal("a case note reusing a filler id must be refused")
+	}
+	f.Filler = append(f.Filler, StoredNote{ID: "f1", Text: "..."})
+	if err := checkIDs(Fixture{SchemaVersion: SchemaVersion, Filler: f.Filler}); err == nil {
+		t.Fatal("a duplicate filler id must be refused")
+	}
+	ok := Fixture{
+		SchemaVersion: SchemaVersion,
+		Cases:         []Case{{ID: "ru-001", Notes: []StoredNote{{ID: "n1", Text: "..."}}}},
+		Filler:        []StoredNote{{ID: "f1", Text: "..."}},
+	}
+	if err := checkIDs(ok); err != nil {
+		t.Fatalf("a clean fixture must pass: %v", err)
+	}
+}