From 0e42182ccefd9c55f8e6ecc72e482110c1b1b698 Mon Sep 17 00:00:00 2001
From: Josh Creek <8179928+jcreek@users.noreply.github.com>
Date: Wed, 22 Jul 2026 18:01:21 +0100
Subject: [PATCH] fix(*): jitter kickoff resets to break deterministic
 same-model mirror matches
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GameMode.reset_ball()/reset_ships() teleported to exact, identical spawn
transforms every kickoff. Combined with deterministic bot inference
(action_noise = 0 by default), two ships running the same policy from a
mirror-symmetric state produced mirrored, non-diverging play instead of a
real contest — most visible when both sides use the same exported model.

Adds a small position/yaw jitter (well under anything a player would
notice as "not a real kickoff") so kickoff-style resets stop being
bit-for-bit identical.
---
 Game/scripts/game_mode.gd | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/Game/scripts/game_mode.gd b/Game/scripts/game_mode.gd
index b880f7e6..103617d9 100644
--- a/Game/scripts/game_mode.gd
+++ b/Game/scripts/game_mode.gd
@@ -85,15 +85,36 @@ func spawn_camera_rig(target: Ship) -> ShipCameraRig:
 	return rig
 
 
+# Tiny per-reset randomization, well below anything a player would notice as
+# "not a real kickoff" — just enough that two ships running the identical
+# deterministic AI policy (action_noise = 0) don't start every kickoff from a
+# bit-for-bit mirror-symmetric state. A perfectly symmetric state feeds both
+# controllers identical (canonicalized) observations, so they emit mirrored
+# actions and can lock into a repetitive, non-scoring stalemate — much more
+# visible bot-vs-bot (same model both sides) than bot-vs-human, since a human
+# never satisfies "identical policy" in the first place. See training_mode.gd's
+# _end_eval_episode, which randomizes eval episode states for the same reason.
+const KICKOFF_POSITION_JITTER := 0.3
+const KICKOFF_YAW_JITTER := deg_to_rad(15.0)
+
+
 func reset_ball() -> void:
 	if is_instance_valid(ball):
-		_reset_body(ball, arena.get_ball_spawn())
+		_reset_body(ball, _jittered(arena.get_ball_spawn(), KICKOFF_POSITION_JITTER, 0.0))
 
 
 func reset_ships() -> void:
 	for ship in ships:
 		if is_instance_valid(ship):
-			_reset_body(ship, _ship_spawn_transforms[ship])
+			_reset_body(ship, _jittered(_ship_spawn_transforms[ship], KICKOFF_POSITION_JITTER, KICKOFF_YAW_JITTER))
+
+
+func _jittered(to: Transform3D, position_jitter: float, yaw_jitter: float) -> Transform3D:
+	var offset := Vector3(randf_range(-position_jitter, position_jitter), 0.0, randf_range(-position_jitter, position_jitter))
+	var basis := to.basis
+	if yaw_jitter > 0.0:
+		basis = basis.rotated(Vector3.UP, randf_range(-yaw_jitter, yaw_jitter))
+	return Transform3D(basis, to.origin + offset)
 
 
 func _reset_body(body: RigidBody3D, to: Transform3D) -> void: