Replay system: record and replay race flights

Description

A replay system lets players review their best races, share highlights, and spectate ghost runs on leaderboard positions. This is a differentiating feature for the v1.0 release.

Acceptance Criteria

• During a race, each player's position, velocity, and rotation are sampled every tick and stored in memory
• After the race, the recording is serialized and saved to DB (ReplayEntity) or disk
• /replay <player> <cup> <map> command loads and plays back a recorded race as a ghost (invisible entity following the recorded path)
• Ghost replay is visible to all spectators in the instance
• Replay can be paused and scrubbed by the viewer
• Recordings older than 30 days are auto-pruned (configurable)
• Memory impact: storing 300 ticks × 20 players × ~64 bytes/sample = ~375KB — acceptable

Technical Details

• New RecordingComponent and ReplaySystem in server module
• Serialization: use Gson or a compact binary format
• Ghost entity: Minestom EntityCreature following pre-computed positions
• Replay storage: ReplayEntity in shared/database or flat file under replays/

Dependencies

• "Spectator mode" (Beta) provides the ghost-viewing infrastructure

Estimate

XL

Start by reading the server module and the Spectator mode implementation, then inspect shared/database for the proposed ReplayEntity location. Compare the recording, storage, ghost playback, spectator visibility, scrubbing, and pruning acceptance criteria; the work is done when the full replay flow and configurable retention behavior are implemented.