Root-caused with server trace logs: Walk stance throttles 1 move per 2 ticks and SILENTLY discards early moves (movement.rs apply_move -> try_move, TRACE-only) — under load the test's MoveEast landed exactly 1 tick after MoveNorth and was consumed. Server behavior is correct, deliberate D-053, pinned by Rust tests; production clients re-send while keys are held. Fix: COOLDOWN_TICKS=3 post-ack spacing, same as test_sprint2_proof.gd (T-1068) whose fix never reached this file due to helper copy-paste. Pre-fix repro at run 17/30 under load; post-fix 30/30 stress green + full suite 2956/2956.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>