Add deck rename and duplicate operations

New Catalog::rename_deck / duplicate_deck (duplicating format, commander,
notes, and every deck_cards row under a new name), with tests covering
the UNIQUE(name) collision cases the UI needs to surface as friendly
errors rather than raw SQL messages.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

crates/mtgc-core/src/decks.rs

@@ -48,6 +48,36 @@ impl Catalog {
         Ok(())
     }
 
+    /// Rename a deck. Fails if another deck already has that name (`name` is
+    /// UNIQUE).
+    pub fn rename_deck(&self, id: i64, name: &str) -> Result<()> {
+        self.conn
+            .execute("UPDATE decks SET name = ?1 WHERE id = ?2", params![name, id])?;
+        Ok(())
+    }
+
+    /// Duplicate a deck under a new name: same format/commander/notes, plus a
+    /// copy of every deck_cards row (quantity + commander flag). Fails if
+    /// `new_name` is already taken.
+    pub fn duplicate_deck(&self, id: i64, new_name: &str) -> Result<Deck> {
+        let src = self
+            .get_deck(id)?
+            .ok_or_else(|| crate::error::CoreError::Other(format!("deck {id} not found")))?;
+        self.conn.execute(
+            "INSERT INTO decks(name, format, commander_oracle_id, notes)
+             VALUES (?1, ?2, ?3, ?4)",
+            params![new_name, src.format, src.commander_oracle_id, src.notes],
+        )?;
+        let new_id = self.conn.last_insert_rowid();
+        self.conn.execute(
+            "INSERT INTO deck_cards(deck_id, oracle_id, quantity, is_commander)
+             SELECT ?1, oracle_id, quantity, is_commander FROM deck_cards WHERE deck_id = ?2",
+            params![new_id, id],
+        )?;
+        self.get_deck(new_id)
+            .map(|d| d.expect("just-inserted deck must exist"))
+    }
+
     /// Set how many copies of a card belong to a deck. `quantity <= 0` removes
     /// the card from the deck. Upserts on (deck_id, oracle_id).
     pub fn set_deck_card(
@@ -286,4 +316,57 @@ mod tests {
         cat.delete_deck(d.id).unwrap();
         assert!(cat.card_decks("lightning-bolt").unwrap().is_empty());
     }
+
+    #[test]
+    fn rename_deck_updates_name_and_rejects_duplicates() {
+        let fx = test_support::make();
+        let cat = &fx.catalog;
+        let a = cat.create_deck("Deck A", None).unwrap();
+        cat.create_deck("Deck B", None).unwrap();
+
+        cat.rename_deck(a.id, "Deck A Renamed").unwrap();
+        assert_eq!(cat.get_deck(a.id).unwrap().unwrap().name, "Deck A Renamed");
+
+        // decks.name is UNIQUE.
+        assert!(cat.rename_deck(a.id, "Deck B").is_err());
+    }
+
+    #[test]
+    fn duplicate_deck_copies_metadata_and_cards() {
+        let fx = test_support::make();
+        let cat = &fx.catalog;
+        cat.add_owned("llanowar-elves", 2).unwrap();
+
+        let src = cat.create_deck("Original", Some("llanowar-elves")).unwrap();
+        cat.set_deck_format(src.id, "Commander").unwrap();
+        cat.set_deck_card(src.id, "llanowar-elves", 2, true).unwrap();
+        cat.set_deck_card(src.id, "lightning-bolt", 1, false).unwrap();
+
+        let copy = cat.duplicate_deck(src.id, "Original (copy)").unwrap();
+        assert_eq!(copy.name, "Original (copy)");
+        assert_eq!(copy.format, "Commander");
+        assert_eq!(copy.commander_oracle_id.as_deref(), Some("llanowar-elves"));
+
+        let mut contents: Vec<_> = cat
+            .deck_contents(copy.id)
+            .unwrap()
+            .into_iter()
+            .map(|e| (e.card.oracle_id, e.quantity, e.is_commander))
+            .collect();
+        contents.sort_by(|a, b| a.0.cmp(&b.0));
+        assert_eq!(
+            contents,
+            vec![
+                ("lightning-bolt".to_string(), 1, false),
+                ("llanowar-elves".to_string(), 2, true),
+            ]
+        );
+
+        // The original deck is untouched.
+        let original_contents = cat.deck_contents(src.id).unwrap();
+        assert_eq!(original_contents.len(), 2);
+
+        // Duplicating into an already-taken name fails (UNIQUE).
+        assert!(cat.duplicate_deck(src.id, "Original").is_err());
+    }
 }