Boat Standing Fix

Fixes the vanilla bug (MC-156980) where standing on a boat floating in water makes your movement stutter and rubber-band, or gets you pushed around and stuck.

Root cause

Player movement is client-authoritative: the client simulates its own position and reports it to the server, which recomputes the same movement and rejects (snaps back) the client's position if the two disagree too much. Two checks in the server's movement handling do this, and both misfire when a boat is drifting under the player:

• A tolerance check that a bobbing boat blows through most ticks purely from its own motion, nothing to do with the player.
• A collision check that treats the boat's own shifting hitbox as a new collision every time it moves under the player.

Both checks are loosened, but only when the moving entity is near a boat, so ordinary anti-cheat validation is untouched everywhere else.

Details

• Runs on the server. In singleplayer the integrated server handles it.
• Clients do not need the mod; a vanilla client gets the fix for free once the server runs it.