Keep dinner names frozen in Supply archive posts

Freezing a Supply run now records each group's dinner name in
shopping_groups.frozen_dinner_name, in the same transaction as the
freeze. A frozen list and its Supply archive post read that name, so
renaming a dinner after its week is frozen no longer rewrites the
archive; a current list still shows its dinners' names live.
Migration 0018 adds the column and fills it for lists frozen before it.

Task: 22f80eb6-cdee-4377-80ea-9b28f15a866f

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/shopping/archive.go

@@ -22,7 +22,9 @@ const (
 
 // Freeze moves the Supply run of the week starting weekStart into the
 // Supply archive: its status becomes archived and frozen_at is set, after
-// which it is read-only (Generate and SetNeeded are ErrFrozen). Freezing a
+// which it is read-only (Generate and SetNeeded are ErrFrozen). The list
+// keeps the names its dinners have as it is frozen, so its post in the
+// Supply archive shows them whatever a dinner is renamed later. Freezing a
 // frozen list does nothing and is no error.
 //
 // The week must have ended in the household's time zone: a week not yet
@@ -79,14 +81,25 @@ func (s *Service) freeze(ctx context.Context, weekStart store.LocalDate, now tim
 				"week", list.WeekStart, "list", list.ID, "error", err)
 		}
 	}
-	// A list frozen meanwhile is left as it is: the freeze is done.
+	// A list frozen meanwhile is left as it is, its names as they were
+	// frozen: the freeze is done.
 	stamp := store.Now().String()
-	if _, err := q.FreezeShoppingList(ctx, db.FreezeShoppingListParams{
-		FrozenAt: sql.NullString{String: stamp, Valid: true}, UpdatedAt: stamp, ID: list.ID,
-	}); err != nil {
-		return fmt.Errorf("shopping: freeze %s: %w", weekStart, err)
-	}
-	return nil
+	return s.st.WithTx(ctx, func(tx *sql.Tx) error {
+		q := db.New(tx)
+		n, err := q.FreezeShoppingList(ctx, db.FreezeShoppingListParams{
+			FrozenAt: sql.NullString{String: stamp, Valid: true}, UpdatedAt: stamp, ID: list.ID,
+		})
+		if err != nil {
+			return fmt.Errorf("shopping: freeze %s: %w", weekStart, err)
+		}
+		if n == 0 {
+			return nil
+		}
+		if err := q.FreezeShoppingGroupNames(ctx, list.ID); err != nil {
+			return fmt.Errorf("shopping: freeze %s: keep dinner names: %w", weekStart, err)
+		}
+		return nil
+	})
 }
 
 // freezeTitleJob is the title job of list as Generate would enqueue it:
@@ -145,7 +158,8 @@ type Post struct {
 	Label string
 	// Title is nil while the list is untitled, when Label stands in.
 	Title *string
-	// Dinners are the names of the list's dinners, in day order.
+	// Dinners are the names of the list's dinners, in day order: as they
+	// were when the list was frozen, or as they are now while it is not.
 	Dinners []string
 	// Items is how many items the list has, and OnHand how many of them
 	// the household marked "have it".