- Migrate connection pool from manual LinkedBlockingQueue to HikariCP
(eliminates isValid() ping on every query visible in Spark profiler)
- Move ALL DB writes off server thread: logout uses snapshot+async+latch,
shutdown uses snapshot+CompletableFuture.allOf for parallel saves
- Pre-read curios/accessories/cosmeticarmor/attachments on background
thread during login (4-7 fewer DB queries on main thread per login)
- Auto-save interval increased to 5 minutes
- Fix pool shutdown ordering: shutdownPool() now runs AFTER all shutdown
saves complete (previously could fire before, silently losing all data)
- Fix connection leak in executeQuery/executePreparedQuery when
prepareStatement throws (leaked connections exhaust HikariCP pool)
- Fix duplication bug: saveStorageContents guard used nbt.size()<=1 which
blocked legitimately emptied backpacks from saving to DB
- Fix stale SaveToFile overwriting logout: check playerLocks.containsKey
before writing to prevent stale background task from regressing data
- Remove LIMIT 1000 on startup online=0 reset (could leave players stuck)
- Add executorService.shutdown() on server stop to prevent JVM hang
- Add apply methods (applyCuriosFromData, applyAccessoriesFromData, etc.)
to separate entity writes from DB reads for thread-safe restore
- Add UUID collectors (collectBackpackUuids, collectSSUuids) and
background save methods for snapshot+async logout/shutdown pattern
