feat: Add 'Test Solo' feature to Cube Manager for randomized deck play, with server support for solo game state on rejoin.

docs/development/CENTRAL.md

@@ -82,3 +82,4 @@
 - [Land Advice & Unlimited Time](./devlog/2025-12-17-155500_land_advice_and_unlimited_time.md): Completed. Implemented land suggestion algorithm and disabled deck builder timer.
 - [Deck Builder Magnified View](./devlog/2025-12-17-160500_deck_builder_magnified_view.md): Completed. Added magnified card preview sidebar to deck builder.
 - [Gameplay Magnified View & Timeout](./devlog/2025-12-17-161500_gameplay_magnified_view_and_timeout.md): Completed. Added magnified view with full card details (Oracle text, type, mana) to gameplay and disabled timeout.
+- [Test Deck Feature](./devlog/2025-12-17-162500_test_deck_feature.md): Completed. Implemented "Test Solo" button in Cube Manager to instantly start a solo game with a randomized deck from generated packs.

docs/development/devlog/2025-12-17-162500_test_deck_feature.md

@@ -0,0 +1,32 @@
+# Test Deck Feature Implementation
+
+## Requirements
+- Allow users to "Test Deck" directly from the Cube Manager (Pack Generator).
+- Create a randomized deck from the generated pool (approx. 23 spells + 17 lands).
+- Start a solo game immediately.
+- Enable return to lobby.
+
+## Implementation Details
+
+### Client-Side Updates
+- **`App.tsx`**: Passed `availableLands` to `CubeManager` to allow for proper basic land inclusion in randomized decks.
+- **`CubeManager.tsx`**:
+    - Added `handleStartSoloTest` function.
+    - Logic: Flattens generated packs, separates lands/spells, shuffles and picks 23 spells, adds 17 basic lands (using `availableLands` if available).
+    - Emits `start_solo_test` socket event with the constructed deck.
+    - On success, saves room ID to `localStorage` and navigates to the Lobby tab using `onGoToLobby`.
+    - Added "Test Solo" button to the UI next to "Play Online".
+- **`LobbyManager.tsx`**: Existing `rejoin_room` logic (triggered on mount via `localStorage`) handles picking up the active session.
+
+### Server-Side Updates
+- **`src/server/index.ts`**:
+    - Updated `rejoin_room` handler to emit `game_update` if the room status is `playing`. This ensures that when the client navigates to the lobby and "rejoins" the solo session, the game board is correctly rendered.
+
+## User Flow
+1. User generates packs in Cube Manager.
+2. User clicks "Test Solo".
+3. System builds a random deck and creates a solo room on the server.
+4. UI switches to "Online Lobby" tab.
+5. Lobby Manager detects the active session and loads the Game Room.
+6. User plays the game.
+7. User can click "Leave Room" icon in the sidebar to return to the Lobby creation screen.