fix: remove unused imports and variables from server files to resolve build errors.

docs/development/CENTRAL.md

@@ -140,3 +140,4 @@
 - [Strict Cache Structure](./devlog/2025-12-18-213300_strict_cache_structure.md): Completed. Enforced cache structure `/cards/[code]/full` and `/cards/[code]/crop`, removing the `images` subdirectory and ensuring strict local file usage.
 - [Implicit Image Caching](./devlog/2025-12-18-213900_implicit_image_caching.md): Completed. Updated API routes `/api/sets/:code/cards` and `/api/cards/parse` to implicitly trigger and await image caching, ensuring assets are available immediately for generators.
 - [Restore Images Subdirectory](./devlog/2025-12-18-214300_restore_images_subdir.md): Completed. Corrected cache folder structure to `/cards/images/[set]/full` and `/cards/images/[set]/crop` as per user request.
+- [Fix Build Unused Variables](./devlog/2025-12-19-011500_fix_build_unused_vars.md): Completed. Resolved TS6133 errors in RulesEngine, PersistenceManager, and CardService to fix Docker build failure.

docs/development/devlog/2025-12-19-011500_fix_build_unused_vars.md

@@ -0,0 +1,24 @@
+# Fix Build Unused Variables
+
+## Objective
+Fix Typescript errors preventing `npm run build` execution in the Docker container.
+The errors were `TS6133` (unused variables) in:
+- `server/game/RulesEngine.ts`
+- `server/managers/PersistenceManager.ts`
+- `server/services/CardService.ts`
+
+## Changes
+1. **RulesEngine.ts**:
+   - Removed unused imports: `PlayerState`, `StackObject`.
+   - Renamed unused parameter `playerId` to `_playerId` in `cleanupStep`.
+   - (Also fixed an accidental comment injection during the process).
+
+2. **PersistenceManager.ts**:
+   - Removed unused `__dirname` and `__filename` definitions.
+   - Removed unused `fileURLToPath` import.
+
+3. **CardService.ts**:
+   - Removed unused `fs` import.
+
+## Verification
+- Ran `npx tsc --noEmit` in `src` directory. Result: Exit code 0 (Success).