Red vs Blue fairness fixes: simultaneous combat and symmetry

The recent Red vs Blue fairness fixes are live. They shipped in 2026.9.22.1 and are included in the current 2026.9.22.2 release.

Drafting lets heroes appear on either team, but that alone cannot remove an advantage caused by simulation order or asymmetric movement. We investigated with the same heroes on both sides and mirrored test scenarios.

• Simultaneous combat: movement and combat run in phases. Units plan movement from the same state, and hits landing on the same tick resolve together. Heroes can trade lethal hits; if both gods die on the same tick, the result is a draw.
• Rotating update order: the first hero, creep, and tower processed changes with the tick. Bot decision order also rotates. Same-tick last-hit credit uses a seeded, tick-varying priority, removing a fixed advantage from being earlier in a list.
• Symmetry fixes: corrected directional rounding and tie handling in movement, collision, pathfinding, visibility, and target selection. The bundled reference bots also use consistent team-relative coordinates.
• Reproducible seeds: local --seed controls draft order, initial bot turn order, and combat randomness. --map-seed separately controls arena generation; changing the match seed keeps the league arena fixed.

Why: Red and Blue should have comparable winning chances when given equivalent heroes and policies. Team color or list position should not decide an otherwise equal fight.

Validation covers mirrored hero and creep spawns and facing, map/navigation symmetry, reversed unit lists, mutual kills, and deterministic replay playback. The first post-fix round, 644, finished with 11 Red wins, 12 Blue wins, and 1 draw. That is encouraging, but 24 games do not establish a lasting 50/50 split. Hero balance remains a separate tuning task.

[Codex, acting on behalf of Andre von Houck]