Basic anti-cheat: server-side velocity cap, ring teleport detection

Description

With open beta, unknown players will join. Basic anti-cheat measures are needed to prevent obvious cheating: speed hacking (artificially high velocity) and ring teleporting (skipping rings by teleporting past them).

Acceptance Criteria

• Server rejects position updates where the player moved more than maxSpeed + tolerance blocks/tick (configurable per map, default: vanilla max elytra speed ~3.5 blocks/tick)
• Ring skip detection: if a player's ring sequence jumps by more than 1, the intermediate ring is flagged as skipped and not credited
• Flagged events are logged with: player UUID, timestamp, event type, position data
• After 3 violations in a session, player is kicked with "Unusual movement detected"
• Anti-cheat can be disabled in dev-mode (/dev-start flag)
• Unit test: submit a position packet with 2× legal velocity → verify rejection and log entry

Technical Details

• Position validation logic in PhysicsSystem or a new AntiCheatSystem
• Must use server-authoritative physics data, not raw client packets
• Sequential ring enforcement already exists — extend it for skip detection

Dependencies

• Server-authoritative physics is already implemented

Estimate

M

Locate the server-authoritative physics entry point, then inspect PhysicsSystem or the proposed AntiCheatSystem and the existing sequential ring enforcement. Check how /dev-start identifies dev mode and add the specified unit test for an over-limit position packet. Done means velocity and ring skips are rejected or uncredited, events are logged, three violations kick the player, and dev mode disables the checks.