99df2c09

By: Michael Lynch <git@mtlynch.io>

Predict the local player between snapshots

Rendering the local sprite only from server snapshots meant its
position stepped at 20 Hz, and no client-side movement filled the
frames between. The walk read as choppy compared to the client-only
version on master.

The sprite now runs on an Arcade Physics body driven by input velocity,
so motion integrates at Phaser's fixed step. Server snapshots stash the
divergence as a decaying correction rather than teleporting the sprite.
Correction is only applied on axes the player isn't actively driving —
on a driven axis the gap is expected RTT-worth of lag, and consuming it
would visibly slow the sprite below its intended speed.

The one architectural cost is that PLAYER_SPEED now lives on both sides
of the wire again; a comment in game-scene.ts calls out the pairing
with state.ex.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

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