fix(backend): delete migration losers before winner rewrite

backend/store_test.go

@@ -983,3 +983,54 @@ func TestOpenStoreMigratesAsuraBuildHashKeys(t *testing.T) {
 	}
 	third.Close()
 }
+
+// A hashed row and a pre-existing hashless row of the same series collide on
+// the stripped key. The winner rewrite must happen only after the loser is
+// gone, or the UPDATE hits a primary-key collision and OpenStore fails.
+func TestOpenStoreMigratesAsuraHashlessCollision(t *testing.T) {
+	dbPath := filepath.Join(t.TempDir(), "collision.db")
+
+	store, err := OpenStore(dbPath)
+	if err != nil {
+		t.Fatalf("open: %v", err)
+	}
+	seed := []Bookmark{
+		{Key: "asura:overgeared", Site: "asura", SeriesID: "overgeared",
+			Title: "Hashless", LastChapterNum: 10, UpdatedAt: 100},
+		{Key: "asura:overgeared-059befe1", Site: "asura",
+			SeriesID: "overgeared-059befe1", Title: "Hashed newer",
+			LastChapterNum: 20, UpdatedAt: 200},
+	}
+	for _, b := range seed {
+		if _, err := store.Upsert(b); err != nil {
+			t.Fatalf("seed %s: %v", b.Key, err)
+		}
+	}
+	if err := store.Close(); err != nil {
+		t.Fatalf("close: %v", err)
+	}
+
+	reopened, err := OpenStore(dbPath)
+	if err != nil {
+		t.Fatalf("reopen: %v", err)
+	}
+	t.Cleanup(func() { reopened.Close() })
+
+	list, err := reopened.List()
+	if err != nil {
+		t.Fatalf("List: %v", err)
+	}
+	if len(list) != 1 {
+		t.Fatalf("want 1 row after merge, got %d: %+v", len(list), list)
+	}
+	merged := list[0]
+	if merged.Key != "asura:overgeared" {
+		t.Fatalf("merged key = %q, want asura:overgeared", merged.Key)
+	}
+	if merged.SeriesID != "overgeared" {
+		t.Fatalf("series_id = %q, want overgeared", merged.SeriesID)
+	}
+	if merged.Title != "Hashed newer" || merged.LastChapterNum != 20 || merged.UpdatedAt != 200 {
+		t.Fatalf("merge kept wrong row: %+v", merged)
+	}
+}