fix(assets): remove unreferenced duplicate planet_surface texture

assets/textures/planet_surface.png was byte-identical to and unused
in favor of assets/models/nebula_planet_planet_surface.png, the
sidecar Godot's glTF importer actually extracted from nebula_planet.glb
and uses at runtime. Deleted the orphan (+ its .import) and stopped
gen_planet_surface.py from writing it.

Also measured nebula_dust.gdshader's per-fragment depth-texture sample
cost (~0.07ms/frame at 500 particles, within noise) -- negligible, so
no budgeting concern for further particle work.

Game/assets/textures/planet_surface.png.import

@@ -1,40 +0,0 @@
-[remap]
-
-importer="texture"
-type="CompressedTexture2D"
-uid="uid://bxsadfd04v6r2"
-path="res://.godot/imported/planet_surface.png-d3aaf8310508e4c85b26a3d093bcf9c8.ctex"
-metadata={
-"vram_texture": false
-}
-
-[deps]
-
-source_file="res://assets/textures/planet_surface.png"
-dest_files=["res://.godot/imported/planet_surface.png-d3aaf8310508e4c85b26a3d093bcf9c8.ctex"]
-
-[params]
-
-compress/mode=0
-compress/high_quality=false
-compress/lossy_quality=0.7
-compress/uastc_level=0
-compress/rdo_quality_loss=0.0
-compress/hdr_compression=1
-compress/normal_map=0
-compress/channel_pack=0
-mipmaps/generate=false
-mipmaps/limit=-1
-roughness/mode=0
-roughness/src_normal=""
-process/channel_remap/red=0
-process/channel_remap/green=1
-process/channel_remap/blue=2
-process/channel_remap/alpha=3
-process/fix_alpha_border=true
-process/premult_alpha=false
-process/normal_map_invert_y=false
-process/hdr_as_srgb=false
-process/hdr_clamp_exposure=false
-process/size_limit=0
-detect_3d/compress_to=1

Game/scenes/arena_01_elevated.tscn

@@ -8,13 +8,13 @@
 goal_mode = 1
 
 [node name="GoalTeam0" parent="." index="5"]
-transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 6.0, 18)
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 9.0, 27)
 
 [node name="GoalTeam1" parent="." index="6"]
-transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, 0, 6.0, -18)
+transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, 0, 9.0, -27)
 
 [node name="Spawn1" parent="SpawnsTeam0" index="0"]
-transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 4.0, 2.8, 13.5)
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 6.0, 2.8, 20.25)
 
 [node name="Spawn1" parent="SpawnsTeam1" index="0"]
-transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, -4.0, 2.8, -13.5)
+transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, -6.0, 2.8, -20.25)

Game/scenes/arena_02.tscn

@@ -32,7 +32,7 @@ gradient = SubResource("Gradient_dust")
 
 [sub_resource type="ParticleProcessMaterial" id="ParticleProcessMaterial_dust"]
 emission_shape = 3
-emission_box_extents = Vector3(26, 11, 28)
+emission_box_extents = Vector3(39, 16.5, 42)
 direction = Vector3(0, 1, 0)
 spread = 180.0
 initial_velocity_min = 0.1
@@ -68,48 +68,48 @@ light_color = Color(0.55, 0.35, 0.65, 1)
 light_energy = 0.45
 
 [node name="NebulaDust" type="GPUParticles3D" parent="."]
-transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 5, 0)
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 7.5, 0)
 amount = 500
 lifetime = 22.0
 preprocess = 8.0
 randomness = 1.0
-visibility_aabb = AABB(-30, -14, -32, 60, 28, 64)
+visibility_aabb = AABB(-45, -21, -48, 90, 42, 96)
 process_material = SubResource("ParticleProcessMaterial_dust")
 draw_pass_1 = SubResource("QuadMesh_dust")
 
 [node name="Decoration" type="Node3D" parent="."]
 
 [node name="NebulaStationA" parent="Decoration" instance=ExtResource("8_station")]
-transform = Transform3D(1.8, 0, 0, 0, 1.8, 0, 0, 0, 1.8, 28, 5, -6)
+transform = Transform3D(1.8, 0, 0, 0, 1.8, 0, 0, 0, 1.8, 42, 7.5, -9)
 rotation = Vector3(0, -0.436332, 0)
 
 [node name="NebulaDebrisA" parent="Decoration" instance=ExtResource("9_debris")]
-transform = Transform3D(1.2, 0, 0, 0, 1.2, 0, 0, 0, 1.2, -22, 9, 11)
+transform = Transform3D(1.2, 0, 0, 0, 1.2, 0, 0, 0, 1.2, -33, 13.5, 16.5)
 rotation = Vector3(0.261799, 0.698132, 0.087266)
 
 [node name="NebulaDebrisB" parent="Decoration" instance=ExtResource("9_debris")]
-transform = Transform3D(0.8, 0, 0, 0, 0.8, 0, 0, 0, 0.8, 34, 3, 15)
+transform = Transform3D(0.8, 0, 0, 0, 0.8, 0, 0, 0, 0.8, 51, 4.5, 22.5)
 rotation = Vector3(-0.174533, 1.919862, 0.349066)
 
 [node name="NebulaDebrisC" parent="Decoration" instance=ExtResource("9_debris")]
-transform = Transform3D(1.5, 0, 0, 0, 1.5, 0, 0, 0, 1.5, -30, 11, -21)
+transform = Transform3D(1.5, 0, 0, 0, 1.5, 0, 0, 0, 1.5, -45, 16.5, -31.5)
 rotation = Vector3(0.087266, -1.047198, -0.261799)
 
 [node name="NebulaStationB" parent="Decoration" instance=ExtResource("8_station")]
-transform = Transform3D(1.5, 0, 0, 0, 1.5, 0, 0, 0, 1.5, -32, 7, 9)
+transform = Transform3D(1.5, 0, 0, 0, 1.5, 0, 0, 0, 1.5, -48, 10.5, 13.5)
 rotation = Vector3(0.05, 1.134464, -0.02)
 
 [node name="NebulaStationC" parent="Decoration" instance=ExtResource("8_station")]
-transform = Transform3D(1.3, 0, 0, 0, 1.3, 0, 0, 0, 1.3, 9, 8, 42)
+transform = Transform3D(1.3, 0, 0, 0, 1.3, 0, 0, 0, 1.3, 13.5, 12, 63)
 rotation = Vector3(-0.03, 2.740167, 0.06)
 
 [node name="NebulaDebrisD" parent="Decoration" instance=ExtResource("9_debris")]
-transform = Transform3D(1.0, 0, 0, 0, 1.0, 0, 0, 0, 1.0, 13, 15, -35)
+transform = Transform3D(1.0, 0, 0, 0, 1.0, 0, 0, 0, 1.0, 19.5, 22.5, -52.5)
 rotation = Vector3(0.4, 1.3, -0.2)
 
 [node name="NebulaDebrisE" parent="Decoration" instance=ExtResource("9_debris")]
-transform = Transform3D(0.9, 0, 0, 0, 0.9, 0, 0, 0, 0.9, -11, 4, 33)
+transform = Transform3D(0.9, 0, 0, 0, 0.9, 0, 0, 0, 0.9, -16.5, 6, 49.5)
 rotation = Vector3(-0.3, -0.9, 0.15)
 
 [node name="NebulaPlanet" parent="Decoration" instance=ExtResource("11_planet")]
-transform = Transform3D(30, 0, 0, 0, 30, 0, 0, 0, 30, -55, 38, -80)
+transform = Transform3D(30, 0, 0, 0, 30, 0, 0, 0, 30, -82.5, 57, -120)

Game/scenes/arena_02_elevated.tscn

@@ -8,13 +8,13 @@
 goal_mode = 1
 
 [node name="GoalTeam0" parent="." index="5"]
-transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 6.0, 18)
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 9.0, 27)
 
 [node name="GoalTeam1" parent="." index="6"]
-transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, 0, 6.0, -18)
+transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, 0, 9.0, -27)
 
 [node name="Spawn1" parent="SpawnsTeam0" index="0"]
-transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 4.0, 2.8, 13.5)
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 6.0, 2.8, 20.25)
 
 [node name="Spawn1" parent="SpawnsTeam1" index="0"]
-transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, -4.0, 2.8, -13.5)
+transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, -6.0, 2.8, -20.25)

Game/scenes/arena_03_elevated.tscn

@@ -8,13 +8,13 @@
 goal_mode = 1
 
 [node name="GoalTeam0" parent="." index="5"]
-transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 6.0, 18)
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 9.0, 27)
 
 [node name="GoalTeam1" parent="." index="6"]
-transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, 0, 6.0, -18)
+transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, 0, 9.0, -27)
 
 [node name="Spawn1" parent="SpawnsTeam0" index="0"]
-transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 4.0, 2.8, 13.5)
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 6.0, 2.8, 20.25)
 
 [node name="Spawn1" parent="SpawnsTeam1" index="0"]
-transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, -4.0, 2.8, -13.5)
+transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, -6.0, 2.8, -20.25)

Game/scenes/arena_base.tscn

@@ -53,16 +53,16 @@ shadow_enabled = false
 environment = SubResource("Environment_base")
 
 [node name="ReflectionProbe" type="ReflectionProbe" parent="."]
-transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 6, 0)
-size = Vector3(26, 14, 40)
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 9, 0)
+size = Vector3(38, 20, 58)
 box_projection = true
 update_mode = 0
 
 [node name="GoalTeam0" parent="." instance=ExtResource("6_p57ef")]
-transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0.79, 18)
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0.79, 27)
 
 [node name="GoalTeam1" parent="." instance=ExtResource("6_p57ef")]
-transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, 0, 0.79, -18)
+transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, 0, 0.79, -27)
 team = 1
 
 [node name="BallSpawn" type="Marker3D" parent="."]
@@ -71,9 +71,33 @@ transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 2, 0)
 [node name="SpawnsTeam0" type="Node3D" parent="."]
 
 [node name="Spawn1" type="Marker3D" parent="SpawnsTeam0"]
-transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 2.8, 13.5)
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, -9, 2.8, 20.25)
+
+[node name="Spawn2" type="Marker3D" parent="SpawnsTeam0"]
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, -4.5, 2.8, 20.25)
+
+[node name="Spawn3" type="Marker3D" parent="SpawnsTeam0"]
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 2.8, 20.25)
+
+[node name="Spawn4" type="Marker3D" parent="SpawnsTeam0"]
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 4.5, 2.8, 20.25)
+
+[node name="Spawn5" type="Marker3D" parent="SpawnsTeam0"]
+transform = Transform3D(1, 0, 0, 0, 1, 0, 0, 0, 1, 9, 2.8, 20.25)
 
 [node name="SpawnsTeam1" type="Node3D" parent="."]
 
 [node name="Spawn1" type="Marker3D" parent="SpawnsTeam1"]
-transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, 0, 2.8, -13.5)
+transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, -9, 2.8, -20.25)
+
+[node name="Spawn2" type="Marker3D" parent="SpawnsTeam1"]
+transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, -4.5, 2.8, -20.25)
+
+[node name="Spawn3" type="Marker3D" parent="SpawnsTeam1"]
+transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, 0, 2.8, -20.25)
+
+[node name="Spawn4" type="Marker3D" parent="SpawnsTeam1"]
+transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, 4.5, 2.8, -20.25)
+
+[node name="Spawn5" type="Marker3D" parent="SpawnsTeam1"]
+transform = Transform3D(-1, 0, 0, 0, 1, 0, 0, 0, -1, 9, 2.8, -20.25)

Game/scripts/ai_ship_controller.gd

@@ -35,7 +35,8 @@ var _action := ShipAction.new()
 var _ticks_until_decision := 0
 
 var _ship: Ship
-var _opponent: Ship
+var _teammates: Array[Ship] = []
+var _opponents: Array[Ship] = []
 var _ball: RigidBody3D
 var _attack_goal_position: Vector3
 var _scene_refs_ready := false
@@ -60,7 +61,7 @@ func get_action() -> ShipAction:
 
 
 func _decide() -> void:
-	var obs := ShipObservations.build(_ship, _opponent, _ball, _attack_goal_position)
+	var obs := ShipObservations.build(_ship, _teammates, _opponents, _ball, _attack_goal_position)
 	var out := _policy.forward(obs)
 	# See ShipActionCodec for the decode — the single source of truth shared
 	# with the training side, so this must never reimplement layout/ordering
@@ -76,21 +77,40 @@ func _decide() -> void:
 		_action = ShipActionCodec.from_logits(out, action_noise)
 
 
-# Find ship/ball/opponent/goal once everything is spawned. ShipAction axes
-# are body-frame so only observations need team context (ShipObservations).
+# Find ship/ball/teammates/opponents/goal once everything is spawned.
+# ShipAction axes are body-frame so only observations need team context
+# (ShipObservations). Rosters never change mid-match (no despawn path exists
+# anywhere in this codebase), so this only needs to run once — sorted by
+# spawn_index so a given ship keeps the same observation slot for the whole
+# match, matching TrainingMode's identically-sorted lists.
 func _discover_scene_refs() -> bool:
 	_ship = get_parent() as Ship
 	if _ship == null or not is_inside_tree():
 		return false
 	_ball = get_tree().get_first_node_in_group("ball")
+	if _ball == null:
+		return false
+	# Cleared, not just appended to: if an earlier call reached this point but
+	# a later check still failed, a retry must not re-append onto whatever it
+	# already collected — that would duplicate every ship in the roster.
+	_teammates.clear()
+	_opponents.clear()
 	for node in get_tree().get_nodes_in_group("ship"):
-		if node != _ship:
-			_opponent = node
-			break
+		var other := node as Ship
+		if other == _ship:
+			continue
+		if other.team == _ship.team:
+			_teammates.append(other)
+		else:
+			_opponents.append(other)
+	_teammates.sort_custom(_by_spawn_index)
+	_opponents.sort_custom(_by_spawn_index)
 	for goal in get_tree().get_nodes_in_group("goal"):
 		if goal.team == 1 - _ship.team:
 			_attack_goal_position = goal.global_position
-	if _ball == null:
-		return false
 	_scene_refs_ready = true
 	return true
+
+
+static func _by_spawn_index(a: Ship, b: Ship) -> bool:
+	return a.spawn_index < b.spawn_index

Game/scripts/arena_boundary.gd

@@ -5,9 +5,9 @@ extends StaticBody3D
 # instances objects/arena_boundary.tscn so all arenas share one size; code
 # that needs field dimensions derives them from these constants rather than
 # restating numbers.
-const INNER_HALF_X := 12.0
-const INNER_HALF_Z := 18.0
-const INNER_HEIGHT := 12.0
+const INNER_HALF_X := 18.0
+const INNER_HALF_Z := 27.0
+const INNER_HEIGHT := 18.0
 # Goal-centre distance from arena centre. Flush with the end walls (see
 # arena_01.tscn's goal transforms), so there is no floating gap between the
 # goal and the wall for a ball to ramp across before reaching the sensor.
@@ -45,14 +45,30 @@ const BASE_RADIUS := 2.0
 # The end-wall fillets stop short of the goal mouth so floor-level shots
 # roll flat into the goal sensor (3.5 m wide) instead of ramping over it.
 const GOAL_MOUTH_HALF_WIDTH := 2.5
-# The aperture the visual shell leaves for the goal itself, and the opaque
-# bulkhead surrounding it. Mirrors objects/goal.tscn's 3.5 x 1.5 sensor with a
-# little clearance, so no sliver of panel shows through the goal frame. The
-# surround has to be opaque hull: backed by the translucent field panel
+# The real navigable hole in the wall's collision (see
+# _build_end_wall_colliders) — must track objects/goal.tscn's BoxShape3D
+# (3.5 x 1.5, i.e. half-width 1.75, height 1.5) exactly. Anything wider than
+# the scoring sensor lets the ball cross the wall opening without entering
+# the sensor and failing to score; this is collision-authoritative, do not
+# widen it for cosmetic reasons — see GOAL_VISUAL_APERTURE_* below for that.
+# Half-width matches the sensor exactly; height is a few cm off in FLOOR mode
+# (the sensor is vertically offset by the goal node's own y=0.79 placement,
+# while the hole itself is measured from the floor at y=0 — see
+# _goal_surround_bounds), which is immaterial at the ball's radius but means
+# "exact match" isn't literally true.
+const GOAL_APERTURE_HALF_WIDTH := 1.75
+const GOAL_APERTURE_HEIGHT := 1.5
+# The (larger) aperture the visual shell/opaque bulkhead actually cuts —
+# deliberately wider than the true collision hole above, so goal.gd's bezel/
+# rim frame (built starting exactly at the sensor's own half-extents) has
+# clearance to be seen against the hull's cut edge instead of sitting flush
+# with it. Cosmetic only: collision still uses the exact GOAL_APERTURE_*
+# pair above, so this can't reopen the "ball crosses without scoring" bug.
+const GOAL_VISUAL_APERTURE_HALF_WIDTH := GOAL_APERTURE_HALF_WIDTH + 0.1
+const GOAL_VISUAL_APERTURE_HEIGHT := GOAL_APERTURE_HEIGHT + 0.15
+# The surround has to be opaque hull: backed by the translucent field panel
 # instead, the goal's recess and net showed straight through the wall beside
 # the mouth and read as a second, duplicated net.
-const GOAL_APERTURE_HALF_WIDTH := 1.85
-const GOAL_APERTURE_HEIGHT := 1.65
 # ELEVATED only — in FLOOR mode the surround spans the deck to the fillet
 # tangent, so its height is BASE_RADIUS and needs no constant.
 const GOAL_SURROUND_HALF_HEIGHT := 1.6
@@ -102,12 +118,28 @@ var _field_material: ShaderMaterial
 # pattern so the viewport lookup isn't repeated every frame.
 var _camera: Camera3D
 
+# Group every generated collider is tagged with. A CollisionShape3D only
+# registers a shape with a CollisionObject3D that is its DIRECT parent — an
+# earlier version of this code grouped generated colliders under an
+# intermediate Node3D container for identification, which silently made
+# every one of them inert (no shape ever reached the StaticBody3D). They must
+# be direct children of `self`; the group tag is how bake_colliders()
+# identifies (and clears, for idempotent re-baking) its own prior output
+# without an intermediate node.
+const GENERATED_COLLIDER_GROUP := "_arena_generated_collider"
+
 
 func _ready() -> void:
 	add_to_group("arena_boundary")
-	_build_corner_colliders()
-	_build_fillet_colliders(BASE_FILLET)
-	_build_fillet_colliders(CEILING_FILLET)
+	# goal_mode affects the generated geometry itself (see _fillet_runs'
+	# `split` and _build_end_wall_colliders' hole placement), but it's an
+	# instance-level override each arena_0X_elevated.tscn applies to the
+	# shared arena_boundary.tscn's Boundary node — so a bake done in FLOOR
+	# mode (the shared .tscn's default) must not be silently reused by an
+	# ELEVATED instance. Only skip regenerating when the existing bake was
+	# actually made in the current goal_mode.
+	if get_meta("baked_goal_mode", -1) != goal_mode:
+		bake_colliders()
 	# Visuals are pure decoration and training spawns many headless instances
 	# that never render one, so skip the mesh build there entirely. Collision
 	# is unaffected either way.
@@ -117,6 +149,29 @@ func _ready() -> void:
 	_build_visual_shell()
 
 
+# Builds every generated collider (corner curves, base/ceiling fillets, end-
+# wall goal holes) as direct children of this ArenaBoundary (required for
+# them to register with the StaticBody3D at all) and records the goal_mode
+# they were built for. Idempotent: clears any of its own prior output first
+# (identified via GENERATED_COLLIDER_GROUP), so calling this repeatedly — a
+# stale bake whose goal_mode doesn't match (see _ready), or re-running
+# tools/bake_arena_boundary.gd on an already-baked scene — replaces rather
+# than duplicates. _ready() calls this itself for any scene that hasn't been
+# baked yet, so behaviour is identical either way; baking only skips redoing
+# this work on every subsequent load, which matters most for the many
+# parallel headless training envs that would otherwise pay it on every
+# episode reset.
+func bake_colliders() -> void:
+	for child in get_children():
+		if child.is_in_group(GENERATED_COLLIDER_GROUP):
+			child.free()
+	_build_corner_colliders()
+	_build_fillet_colliders(BASE_FILLET)
+	_build_fillet_colliders(CEILING_FILLET)
+	_build_end_wall_colliders()
+	set_meta("baked_goal_mode", goal_mode)
+
+
 # Wall+ceiling-only proximity force field ("artificial gravity" grav-plating,
 # weaker than the floor's plain default gravity, which this deliberately
 # leaves untouched). Ship and Ball each call this with their own
@@ -248,8 +303,10 @@ func _fillet_runs(rise: float) -> Array[Dictionary]:
 
 
 # --- collision ---------------------------------------------------------------
-# These build the tangent-box collider rings only. Their geometry is what
-# trained policies in Game/bots/ were fitted against, so it must not change.
+# Builds the tangent-box collider rings and each end wall's real goal hole.
+# Geometry is free to evolve now that bots are retrained from scratch — just
+# re-run tools/bake_arena_boundary.gd afterward so the baked scene (see
+# bake_colliders) reflects the change.
 
 
 # Vertical quarter-cylinder curves across the four wall-wall corners.
@@ -332,9 +389,65 @@ func _add_curve_collider(
 	box.size = Vector3(SURFACE_THICKNESS, run_length, face_width)
 	collision.shape = box
 	collision.transform = Transform3D(segment_basis, origin)
+	collision.add_to_group(GENERATED_COLLIDER_GROUP)
 	add_child(collision)
 
 
+# A plain axis-aligned box collider centred on `center`. Used for the flat
+# end-wall panels below, which aren't tangent to a curve so don't need
+# _add_curve_collider's outward/along framing.
+func _add_box_collider(center: Vector3, size: Vector3) -> void:
+	var collision := CollisionShape3D.new()
+	var box := BoxShape3D.new()
+	box.size = size
+	collision.shape = box
+	collision.transform = Transform3D(Basis.IDENTITY, center)
+	collision.add_to_group(GENERATED_COLLIDER_GROUP)
+	add_child(collision)
+
+
+# One rectangular end-wall panel spanning x in [x0, x1] and y in [y0, y1] at
+# the given wall_z, SURFACE_THICKNESS deep. No-ops for a degenerate (zero or
+# negative area) range, which happens whenever the goal hole's aperture
+# extends to the wall's own boundary (e.g. FLOOR mode's aperture bottom sits
+# at the wall's own y0).
+func _add_end_wall_panel(wall_z: float, x0: float, x1: float, y0: float, y1: float) -> void:
+	if x1 <= x0 or y1 <= y0:
+		return
+	_add_box_collider(
+		Vector3((x0 + x1) / 2.0, (y0 + y1) / 2.0, wall_z),
+		Vector3(x1 - x0, y1 - y0, SURFACE_THICKNESS)
+	)
+
+
+# Real navigable hole in each end wall, sized to the goal's actual scoring
+# aperture (GOAL_APERTURE_HALF_WIDTH/HEIGHT, which now track
+# objects/goal.tscn's sensor — see that constant's comment) instead of the
+# previous single solid box that let the ball trigger the goal sensor but
+# never actually fly through the wall. _goal_surround_bounds() already knows
+# the aperture's vertical placement for both FLOOR (floor-level) and ELEVATED
+# (raised) goal modes, so this works unmodified for either. Left/right panels
+# carry the full wall height; top/bottom panels close off the remainder of
+# the aperture band above/below the hole. In FLOOR mode the bottom panel
+# (y -1..0) is a harmless duplicate — FloorShape already occupies that
+# region — rather than a true no-op: _add_end_wall_panel still emits it,
+# since aperture_bottom (0) is above y_bottom (-1). Left in rather than
+# special-cased since it costs one extra collider and can't create a gap.
+func _build_end_wall_colliders() -> void:
+	var half_width := INNER_HALF_X + 1.0
+	var y_bottom := -1.0
+	var y_top := INNER_HEIGHT
+	var bounds := _goal_surround_bounds(GOAL_APERTURE_HEIGHT)
+	var aperture_bottom: float = bounds.z
+	var aperture_top: float = bounds.w
+	for sz in [-1.0, 1.0]:
+		var wall_z: float = sz * (INNER_HALF_Z + 0.5)
+		_add_end_wall_panel(wall_z, -half_width, -GOAL_APERTURE_HALF_WIDTH, y_bottom, y_top)
+		_add_end_wall_panel(wall_z, GOAL_APERTURE_HALF_WIDTH, half_width, y_bottom, y_top)
+		_add_end_wall_panel(wall_z, -GOAL_APERTURE_HALF_WIDTH, GOAL_APERTURE_HALF_WIDTH, aperture_top, y_top)
+		_add_end_wall_panel(wall_z, -GOAL_APERTURE_HALF_WIDTH, GOAL_APERTURE_HALF_WIDTH, y_bottom, aperture_bottom)
+
+
 # --- visual shell ------------------------------------------------------------
 # One mesh covering the inner surface of the play volume exactly once. Every
 # piece is cut to meet its neighbours edge-on, so no two translucent surfaces
@@ -444,21 +557,27 @@ func _add_goal_aprons(st: SurfaceTool) -> void:
 # panel, the recess and net behind it showed through the wall and the net read
 # as duplicated either side of the frame.
 func _add_goal_surrounds(st: SurfaceTool) -> void:
-	var bounds := _goal_surround_bounds()
+	var bounds := _goal_surround_bounds(GOAL_VISUAL_APERTURE_HEIGHT)
 	for side in [-1.0, 1.0]:
 		_add_aperture_panel(st,
 			Vector3(0, 0, side * INNER_HALF_Z), Vector3(-side, 0, 0), Vector3.UP,
 			Vector3(0, 0, -side), GOAL_MOUTH_HALF_WIDTH, bounds.x, bounds.y,
-			GOAL_APERTURE_HALF_WIDTH, bounds.z, bounds.w)
+			GOAL_VISUAL_APERTURE_HALF_WIDTH, bounds.z, bounds.w)
 
 
 # (surround bottom, surround top, aperture bottom, aperture top) on the end
 # wall. In FLOOR mode the surround spans deck to fillet tangent with the goal
 # sitting on the deck; in ELEVATED it is a band centred on the raised goal.
-func _goal_surround_bounds() -> Vector4:
+# `aperture_height` is the caller's choice of GOAL_APERTURE_HEIGHT (the true,
+# collision-matching size — see _build_end_wall_colliders) or
+# GOAL_VISUAL_APERTURE_HEIGHT (the cosmetically-widened cut — see
+# _add_goal_surrounds); it only affects the returned aperture bottom/top
+# (z/w), not the surround bottom/top (x/y), which are independent of it in
+# both modes.
+func _goal_surround_bounds(aperture_height: float) -> Vector4:
 	if goal_mode == GoalMode.FLOOR:
-		return Vector4(0.0, BASE_RADIUS, 0.0, GOAL_APERTURE_HEIGHT)
-	var half := GOAL_APERTURE_HEIGHT / 2.0
+		return Vector4(0.0, BASE_RADIUS, 0.0, aperture_height)
+	var half := aperture_height / 2.0
 	return Vector4(
 		GOAL_CENTER_Y - GOAL_SURROUND_HALF_HEIGHT,
 		GOAL_CENTER_Y + GOAL_SURROUND_HALF_HEIGHT,
@@ -485,7 +604,7 @@ func _add_wall_panels(st: SurfaceTool) -> void:
 	var y0 := BASE_RADIUS
 	var y1 := INNER_HEIGHT - BASE_RADIUS
 	var elevated := goal_mode == GoalMode.ELEVATED
-	var bounds := _goal_surround_bounds()
+	var bounds := _goal_surround_bounds(GOAL_VISUAL_APERTURE_HEIGHT)
 	for side in [-1.0, 1.0]:
 		_add_aperture_panel(st,
 			Vector3(side * INNER_HALF_X, 0, 0), Vector3(0, 0, side), Vector3.UP,

Game/scripts/game_mode.gd

@@ -90,6 +90,7 @@ func spawn_ship(team: int, spawn_index: int = 0, controller: ShipController = nu
 	var spawn_transform := spawns[spawn_index] if spawn_index < spawns.size() else Transform3D.IDENTITY
 	ship.global_transform = spawn_transform
 	ship.team = team
+	ship.spawn_index = spawn_index
 	if controller:
 		ship.set_controller(controller)
 	ships.append(ship)
@@ -175,3 +176,37 @@ func _reset_body(body: RigidBody3D, to: Transform3D) -> void:
 func _unhandled_input(event):
 	if event.is_action_pressed("ui_cancel"):
 		get_tree().change_scene_to_file(ScenePaths.MAIN_MENU)
+
+
+# Escape failsafe. The arena is meant to be fully enclosed, but the goal
+# mouths are now a real navigable hole in the end walls (see
+# ArenaBoundary._build_end_wall_colliders) sized to the ball, not the ship —
+# a ship's 1x1 cross-section fits through it, and there is nothing behind the
+# net to stop it. Previously this only existed in TrainingMode (a physics
+# regression there just wastes training time); now that any ship can
+# genuinely fly out through an open goal, every mode needs it, or a stray
+# ship/ball falls into the void with no way back short of quitting. Runs by
+# default every tick; TrainingMode overrides _physics_process entirely and
+# calls this itself alongside its own episode logic.
+const ESCAPE_MARGIN := 15.0
+
+
+func _physics_process(_delta: float) -> void:
+	_respawn_escaped_bodies()
+
+
+func _respawn_escaped_bodies() -> void:
+	for ship in ships:
+		if is_instance_valid(ship) and _is_escaped(ship.global_position):
+			push_warning("GameMode: ship escaped the enclosed arena — check boundary colliders")
+			_reset_body(ship, _ship_spawn_transforms[ship])
+	if is_instance_valid(ball) and _is_escaped(ball.global_position):
+		push_warning("GameMode: ball escaped the enclosed arena — check boundary colliders")
+		_reset_body(ball, arena.get_ball_spawn())
+
+
+func _is_escaped(position: Vector3) -> bool:
+	return absf(position.x) > ArenaBoundary.INNER_HALF_X + ESCAPE_MARGIN \
+		or absf(position.z) > ArenaBoundary.INNER_HALF_Z + ESCAPE_MARGIN \
+		or position.y < -ESCAPE_MARGIN \
+		or position.y > ArenaBoundary.INNER_HEIGHT + ESCAPE_MARGIN

Game/scripts/match_mode.gd

@@ -20,6 +20,12 @@ const KICKOFF_COUNTDOWN_SECONDS := 3
 
 @export var match_length_seconds := 150.0
 
+# Ships per team. The player always controls one ship on team 0; every other
+# ship (teammates and the whole opposing team) is AI-controlled — no local
+# multiplayer input. Plumbing only for this pass: there's no menu UI yet to
+# pick a team size above 1.
+@export_range(1, 5) var team_size: int = 1
+
 @export_group("AI opponent")
 # Trained policy for the opponent; empty = inert placeholder ship.
 @export_file("*.json") var bot_model_path: String = ""
@@ -41,7 +47,10 @@ func _start() -> void:
 	spawn_ball()
 	var player_ship := spawn_ship(0, 0, PlayerShipController.new())
 	spawn_camera_rig(player_ship)
-	spawn_ship(1, 0, _make_opponent_controller())
+	for i in range(1, team_size):
+		spawn_ship(0, i, _make_opponent_controller())
+	for i in team_size:
+		spawn_ship(1, i, _make_opponent_controller())
 
 	await _run_kickoff_countdown()
 

Game/scripts/ship.gd

@@ -18,6 +18,7 @@ extends RigidBody3D
 @export var max_angular_speed = 3.0      # Maximum rotation speed
 @export var drag_coefficient = 0.98      # Linear drag (air resistance)
 @export var angular_drag = 0.95          # Rotational drag
+@export var idle_angular_drag = 0.9      # Rotational drag when no rotation input is held
 
 @export_group("Surface Pull")
 @export var wall_pull_strength = 6.0     # Wall grav-plating strength (m/s^2-equivalent)
@@ -57,6 +58,13 @@ var team: int = 0:
 		team = value
 		_apply_team_color()
 
+# This ship's index within its team's roster (0, 1, 2, ...), set once by
+# GameMode.spawn_ship and never changed afterward. The stable identity
+# AIShipController/ShipAIController sort teammates/opponents by, so both
+# training and in-game inference assign the same ship to the same
+# observation-vector slot for the whole match (see ShipObservations).
+var spawn_index: int = -1
+
 # Shared per-team accent material, built once per team and reused by every
 # ship — avoids allocating a fresh StandardMaterial3D from both _ready and
 # the team setter (previously ran at least twice per ship).
@@ -279,12 +287,22 @@ func apply_rotation_forces(state: PhysicsDirectBodyState3D, rotation_input: Vect
 	state.apply_torque(torque)
 
 
+# Scales a per-tick decay multiplier `k` (defined at a 60 Hz reference rate)
+# by the actual elapsed tick time `step`, so `v *= _tick_scaled(k, step)`
+# decays at the same rate per second regardless of physics_ticks_per_second.
+func _tick_scaled(k: float, step: float) -> float:
+	return pow(k, step * 60.0)
+
+
 func apply_drag_and_limits(state: PhysicsDirectBodyState3D, rotation_input: Vector3):
 	# Linear drag (air resistance)
 	# Physics: F_drag = -½ * ρ * v² * C_d * A (drag force equation)
 	# Simplified: v_new = v_old * drag_coefficient (exponential decay)
-	# This simulates air resistance reducing velocity over time
-	state.linear_velocity *= drag_coefficient
+	# This simulates air resistance reducing velocity over time.
+	# _tick_scaled makes the decay rate invariant to the physics tick rate —
+	# drag_coefficient/angular_drag/idle_angular_drag are all defined as the
+	# per-tick multiplier at a 60 Hz reference rate.
+	state.linear_velocity *= _tick_scaled(drag_coefficient, state.step)
 
 	# Angular drag (rotational resistance)
 	# Physics: Similar to linear drag but for rotational motion
@@ -292,10 +310,10 @@ func apply_drag_and_limits(state: PhysicsDirectBodyState3D, rotation_input: Vect
 	# Simplified: ω_new = ω_old * angular_drag (exponential decay)
 	if rotation_input.length() < 0.01:
 		# More drag when not actively rotating to stop quicker
-		state.angular_velocity *= 0.9
+		state.angular_velocity *= _tick_scaled(idle_angular_drag, state.step)
 	else:
 		# Normal drag when actively rotating
-		state.angular_velocity *= angular_drag
+		state.angular_velocity *= _tick_scaled(angular_drag, state.step)
 
 	# Limit maximum speeds
 	# Physics: Terminal velocity concept - maximum achievable speed

Game/scripts/ship_ai_controller.gd

@@ -106,7 +106,8 @@ const MAX_BALL_DISTANCE := sqrt(
 var ship: Ship
 var rl_controller: RLShipController
 var ball: RigidBody3D
-var opponent: Ship
+var teammates: Array[Ship] = []
+var opponents: Array[Ship] = []
 var attack_goal_position: Vector3
 
 # Set directly by TrainingMode (_on_goal_scored / the timeout branch in
@@ -146,12 +147,16 @@ var _air_touches := 0
 
 
 # Wire up references after the ship is spawned. `attack_goal` is the goal
-# this ship scores into (goal.team == opponent's team).
-func setup(p_ship: Ship, p_rl_controller: RLShipController, p_ball: RigidBody3D, p_opponent: Ship, p_attack_goal_position: Vector3) -> void:
+# this ship scores into (goal.team == the opposing team's team).
+func setup(
+	p_ship: Ship, p_rl_controller: RLShipController, p_ball: RigidBody3D,
+	p_teammates: Array[Ship], p_opponents: Array[Ship], p_attack_goal_position: Vector3
+) -> void:
 	ship = p_ship
 	rl_controller = p_rl_controller
 	ball = p_ball
-	opponent = p_opponent
+	teammates = p_teammates
+	opponents = p_opponents
 	attack_goal_position = p_attack_goal_position
 	init(ship)
 
@@ -161,7 +166,7 @@ func setup(p_ship: Ship, p_rl_controller: RLShipController, p_ball: RigidBody3D,
 
 
 func get_obs() -> Dictionary:
-	return {"obs": ShipObservations.build(ship, opponent, ball, attack_goal_position)}
+	return {"obs": ShipObservations.build(ship, teammates, opponents, ball, attack_goal_position)}
 
 
 func get_reward() -> float:

Game/scripts/ship_observations.gd

@@ -11,13 +11,13 @@ extends RefCounted
 # The same rotation must be inverted when interpreting actions (see canon —
 # it is its own inverse).
 
-# Normalization scales. Standard arena volume (see ArenaBoundary): x ±12,
-# z ±18, height 12, goals at z ±18 (flush with the end walls); positions are
+# Normalization scales. Standard arena volume (see ArenaBoundary): x ±18,
+# z ±27, height 18, goals at z ±27 (flush with the end walls); positions are
 # soft-normalized to roughly [-1, 1]. Do not retune without retraining every
 # model in Game/bots/.
-const POSITION_SCALE := Vector3(20.0, 10.0, 20.0)
+const POSITION_SCALE := Vector3(30.0, 15.0, 30.0)
 const BALL_SPEED_SCALE := 30.0
-const GOAL_DISTANCE_SCALE := 40.0
+const GOAL_DISTANCE_SCALE := 60.0
 
 # Contact normals with y above this are floor contact; below it they read as
 # wall (sideways) or ceiling (downward) — mirrors
@@ -26,13 +26,23 @@ const GOAL_DISTANCE_SCALE := 40.0
 # counts as "in contact" for the reward/observation to stay consistent).
 const FLOOR_NORMAL_MIN_Y := 0.7
 
-# Number of floats build() returns; the policy input size. APPEND-ONLY: new
-# features go on the end and existing indices never move, so an old exported
-# model (whose network was trained against a shorter SIZE) still decodes its
-# first N inputs identically when SIZE grows — see PolicyNetwork.forward's
-# input_size slice/guard. Do not retune an *existing* index without
-# retraining every model in Game/bots/.
-const SIZE := 35
+# Fixed roster caps for the padded teammate/opponent slots below — the
+# largest supported match size is 5v5. Slots beyond the real teammate/
+# opponent count are zero-filled, mirroring the old single-opponent's
+# null-zero-fill (see build()). Callers must pass teammates/opponents already
+# sorted by Ship.spawn_index, so a given ship occupies the same slot in every
+# tick's observation for the whole match, in both training and in-game
+# inference (see AIShipController._discover_scene_refs /
+# TrainingMode._start).
+const MAX_TEAMMATES := 4
+const MAX_OPPONENTS := 5
+
+# Number of floats build() returns; the policy input size.
+# 15 (own) + 6 (ball) + 6*MAX_TEAMMATES + 6*MAX_OPPONENTS + 4 (goal) + 4 (contact)
+# Game/bots/promoted/*.json were exported against the old single-opponent,
+# SIZE=35 layout and are not migrated — this is a from-scratch retrain, so
+# those checkpoints are expected to go stale rather than keep decoding.
+const SIZE := 15 + 6 + 6 * MAX_TEAMMATES + 6 * MAX_OPPONENTS + 4 + 4
 
 
 # 180° rotation about Y for team 1; identity for team 0. A proper rotation
@@ -43,8 +53,14 @@ static func canon(v: Vector3, team: int) -> Vector3:
 
 
 # attack_goal_position: centre of the goal this ship is trying to score in
-# (the goal whose `team` == the opponent's team).
-static func build(ship: Ship, opponent: Ship, ball: RigidBody3D, attack_goal_position: Vector3) -> Array:
+# (the goal whose `team` == the opponent's team). teammates/opponents must
+# already be sorted by Ship.spawn_index (ascending) by the caller — see
+# MAX_TEAMMATES/MAX_OPPONENTS's comment for why slot stability matters; this
+# function only pads/truncates to the fixed cap, it doesn't sort.
+static func build(
+	ship: Ship, teammates: Array[Ship], opponents: Array[Ship],
+	ball: RigidBody3D, attack_goal_position: Vector3
+) -> Array:
 	var team := ship.team
 	var obs := []
 
@@ -60,27 +76,23 @@ static func build(ship: Ship, opponent: Ship, ball: RigidBody3D, attack_goal_pos
 	_append(obs, canon(ball_rel, team) / POSITION_SCALE)
 	_append(obs, canon(ball.linear_velocity, team) / BALL_SPEED_SCALE)
 
-	# Opponent, relative to self (zeros if absent, e.g. a 1-ship drill)
-	if is_instance_valid(opponent):
-		var opp_rel := opponent.global_position - ship.global_position
-		_append(obs, canon(opp_rel, team) / POSITION_SCALE)
-		_append(obs, canon(opponent.linear_velocity, team) / ship.max_speed)
-	else:
-		_append(obs, Vector3.ZERO)
-		_append(obs, Vector3.ZERO)
+	# Teammates and opponents, relative to self, each padded/truncated to a
+	# fixed slot count (zeros past the real roster size, e.g. a 1v1 match or
+	# a solo drill) so the vector shape never depends on match size.
+	_append_ship_slots(obs, ship, team, teammates, MAX_TEAMMATES)
+	_append_ship_slots(obs, ship, team, opponents, MAX_OPPONENTS)
 
 	# Goal we are attacking, relative to self
 	var goal_rel := attack_goal_position - ship.global_position
 	_append(obs, canon(goal_rel, team) / POSITION_SCALE)
 	obs.append(goal_rel.length() / GOAL_DISTANCE_SCALE)
 
-	# Own contact state (appended — see SIZE's append-only invariant).
-	# Added for generation 4: ShipAIController's wall_contact_penalty used to
-	# fire on a condition the observation vector couldn't see coming,
-	# leaving the value function to predict a reward with no supporting
-	# signal. Also gives the policy a direct "am I resting on a surface"
-	# signal it can use to push off (a real aerial mechanic), distinct from
-	# inferring it indirectly from position/up-vector.
+	# Own contact state. Added for generation 4: ShipAIController's
+	# wall_contact_penalty used to fire on a condition the observation vector
+	# couldn't see coming, leaving the value function to predict a reward
+	# with no supporting signal. Also gives the policy a direct "am I resting
+	# on a surface" signal it can use to push off (a real aerial mechanic),
+	# distinct from inferring it indirectly from position/up-vector.
 	var normal := contact_normal(ship)
 	_append(obs, canon(normal, team))
 	obs.append(1.0 if normal != Vector3.ZERO else 0.0)
@@ -88,6 +100,26 @@ static func build(ship: Ship, opponent: Ship, ball: RigidBody3D, attack_goal_pos
 	return obs
 
 
+# Appends up to `slot_count` other ships' (relative position, relative
+# velocity) — 6 floats each — zero-filling any slots beyond the real roster
+# size, or beyond slot_count if the roster somehow has more (sorted-by-
+# spawn_index order means truncation drops the highest spawn_index ships,
+# not the nearest ones — acceptable since slot_count already covers the
+# largest supported match size, 5v5).
+static func _append_ship_slots(
+	obs: Array, ship: Ship, team: int, others: Array[Ship], slot_count: int
+) -> void:
+	for i in slot_count:
+		if i < others.size() and is_instance_valid(others[i]):
+			var other := others[i]
+			var rel := other.global_position - ship.global_position
+			_append(obs, canon(rel, team) / POSITION_SCALE)
+			_append(obs, canon(other.linear_velocity, team) / ship.max_speed)
+		else:
+			_append(obs, Vector3.ZERO)
+			_append(obs, Vector3.ZERO)
+
+
 static func _append(obs: Array, v: Vector3) -> void:
 	obs.append(v.x)
 	obs.append(v.y)

Game/scripts/training_mode.gd

@@ -65,6 +65,12 @@ extends GameMode
 # _place_air_drill.
 @export_range(0.0, 1.0) var air_drill_chance := 0.0
 
+# Ships per team. Default 1 preserves every existing curriculum script's 1v1
+# behaviour unchanged; up to 5 matches ShipObservations.MAX_TEAMMATES/
+# MAX_OPPONENTS. Plumbing only for this pass — no 2v2+ curriculum/reward
+# design has been done, so a run above 1 is untested territory.
+@export_range(1, 5) var team_size: int = 1
+
 # Placement bounds for randomized episode starts, derived from the standard
 # enclosure (ArenaBoundary). The inset keeps a randomly oriented ship (1x1x4
 # box, worst-case half-extent ~2.05) from spawning intersecting the walls,
@@ -86,16 +92,17 @@ const CORNER_LIMIT := ArenaBoundary.INNER_HALF_X + ArenaBoundary.INNER_HALF_Z \
 const FILLET_CLEAR_Y := ArenaBoundary.BASE_RADIUS + FIELD_MIN_Y
 const MAX_RANDOM_BALL_SPEED := 12.0
 const MAX_RANDOM_SHIP_SPEED := 8.0
+# Minimum centre-to-centre separation enforced between ships placed in the
+# same randomized reset (team_size > 1) — without it, _place_ships_random/
+# _place_air_drill sample each ship independently and can spawn them
+# interpenetrating. Twice the ~2.05m worst-case rotated half-extent noted
+# above clears any relative orientation; matches arena_base.tscn's spawn
+# marker spacing, which uses the same margin for the same reason.
+const MIN_SHIP_SEPARATION := 4.5
 
 # Sim runs at 60 physics ticks per sim-second regardless of speedup.
 const TICKS_PER_SIM_SECOND := 60.0
 
-# The arena is physically enclosed, so nothing should ever get this far out.
-# If a body escapes anyway (physics regression, boundary edit), it is warned
-# about and respawned with no reward change and no episode end — a multi-hour
-# training run must survive it, and the escape must not shape rewards.
-const ESCAPE_MARGIN := 15.0
-
 var _agents: Array[ShipAIController] = []
 
 # Eval mode state (see header comment)
@@ -152,22 +159,46 @@ func _start() -> void:
 			spawn_ship(team, 0, bot)
 		return
 
-	var ship_team0 := spawn_ship(0, 0, RLShipController.new())
-	var ship_team1: Ship
-	match _opponent_mode:
-		"inert":
-			ship_team1 = spawn_ship(1, 0, ShipController.new())
-			_inert_ships.append(ship_team1)
-		"frozen":
-			var bot := AIShipController.new()
-			bot.model_path = _opponent_model_path
-			ship_team1 = spawn_ship(1, 0, bot)
-		_:
-			ship_team1 = spawn_ship(1, 0, RLShipController.new())
+	var team0_ships: Array[Ship] = []
+	for i in team_size:
+		team0_ships.append(spawn_ship(0, i, RLShipController.new()))
 
-	_attach_agent(ship_team0, ship_team1)
+	# The opponent_mode branch applies uniformly to every ship on team 1: an
+	# "inert"/"frozen" run means the whole opposing team gets that treatment,
+	# not just one ship.
+	var team1_ships: Array[Ship] = []
+	for i in team_size:
+		var ship1: Ship
+		match _opponent_mode:
+			"inert":
+				ship1 = spawn_ship(1, i, ShipController.new())
+				_inert_ships.append(ship1)
+			"frozen":
+				var bot := AIShipController.new()
+				bot.model_path = _opponent_model_path
+				ship1 = spawn_ship(1, i, bot)
+			_:
+				ship1 = spawn_ship(1, i, RLShipController.new())
+		team1_ships.append(ship1)
+
+	# All ships spawn before any agent attaches, so every agent's
+	# teammates/opponents lists see the other side's full roster.
+	for ship in team0_ships:
+		_attach_agent(ship, _other_ships(team0_ships, ship), team1_ships)
 	if _opponent_mode == "self_play":
-		_attach_agent(ship_team1, ship_team0)
+		for ship in team1_ships:
+			_attach_agent(ship, _other_ships(team1_ships, ship), team0_ships)
+
+
+# `roster` minus `ship`, preserving order — rosters are built by spawn_index
+# already, so this stays spawn_index-sorted (see ShipObservations' slot-
+# stability requirement).
+func _other_ships(roster: Array[Ship], ship: Ship) -> Array[Ship]:
+	var others: Array[Ship] = []
+	for s in roster:
+		if s != ship:
+			others.append(s)
+	return others
 
 
 # Shared "--key=value" cmdline scan used by both eval and curriculum parsing.
@@ -260,14 +291,14 @@ func _ai_default(name: String) -> Variant:
 		_: return null
 
 
-func _attach_agent(ship: Ship, opponent: Ship) -> void:
+func _attach_agent(ship: Ship, teammates: Array[Ship], opponents: Array[Ship]) -> void:
 	var agent := ShipAIController.new()
 	agent.name = "ShipAIController"
 	agent.reset_after = int(episode_length_seconds * TICKS_PER_SIM_SECOND)
 	for key in _ai_overrides:
 		agent.set(key, _ai_overrides[key])
 	ship.add_child(agent)
-	agent.setup(ship, ship.controller as RLShipController, ball, opponent, _attack_goal_position(ship.team))
+	agent.setup(ship, ship.controller as RLShipController, ball, teammates, opponents, _attack_goal_position(ship.team))
 	_agents.append(agent)
 
 
@@ -315,29 +346,11 @@ func _physics_process(_delta):
 				# A goal (_on_goal_scored) does NOT do this — a goal is a
 				# genuine terminal, V(s)=0 is correct there.
 				agent.truncated_this_episode = true
-				agent.terminal_obs = ShipObservations.build(agent.ship, agent.opponent, agent.ball, agent.attack_goal_position)
+				agent.terminal_obs = ShipObservations.build(agent.ship, agent.teammates, agent.opponents, agent.ball, agent.attack_goal_position)
 		_reset_episode()
 		return
 
 
-# Escape failsafe: see ESCAPE_MARGIN.
-func _respawn_escaped_bodies() -> void:
-	for ship in ships:
-		if is_instance_valid(ship) and _escaped(ship.global_position):
-			push_warning("TrainingMode: ship escaped the enclosed arena — check boundary colliders")
-			_place_body(ship, _ship_spawn_transforms[ship], Vector3.ZERO, Vector3.ZERO)
-	if is_instance_valid(ball) and _escaped(ball.global_position):
-		push_warning("TrainingMode: ball escaped the enclosed arena — check boundary colliders")
-		_place_body(ball, arena.get_ball_spawn(), Vector3.ZERO, Vector3.ZERO)
-
-
-func _escaped(position: Vector3) -> bool:
-	return absf(position.x) > ArenaBoundary.INNER_HALF_X + ESCAPE_MARGIN \
-		or absf(position.z) > ArenaBoundary.INNER_HALF_Z + ESCAPE_MARGIN \
-		or position.y < -ESCAPE_MARGIN \
-		or position.y > ArenaBoundary.INNER_HEIGHT + ESCAPE_MARGIN
-
-
 func _on_goal_scored(conceding_team: int) -> void:
 	if _eval:
 		_eval_goals[1 - conceding_team] += 1
@@ -416,17 +429,27 @@ func _place_air_drill() -> void:
 	var ball_velocity := _random_direction() * randf_range(0.0, MAX_RANDOM_BALL_SPEED * 0.5)
 	_place_body(ball, Transform3D(Basis.IDENTITY, ball_position), ball_velocity, Vector3.ZERO)
 
+	# Each ship's lateral offset is sampled independently, so with more than
+	# one ship per team (team_size > 1) two could otherwise land within their
+	# own hulls of each other — resample against every ship already placed
+	# this reset (see MIN_SHIP_SEPARATION).
+	var placed: Array[Vector3] = []
 	for ship in ships:
 		if ship in _inert_ships:
 			continue
-		var lateral_offset := Vector3(randf_range(-1, 1), 0.0, randf_range(-1, 1))
-		lateral_offset = lateral_offset.normalized() if lateral_offset.length_squared() > 0.001 else Vector3.FORWARD
-		lateral_offset *= randf_range(6.0, 14.0)
-		var ship_position := Vector3(
-			clampf(ball_position.x + lateral_offset.x, -FIELD_HALF_X, FIELD_HALF_X),
-			randf_range(FIELD_MIN_Y, 4.0),
-			clampf(ball_position.z + lateral_offset.z, -FIELD_HALF_Z, FIELD_HALF_Z)
-		)
+		var ship_position := Vector3.ZERO
+		for _attempt in 20:
+			var lateral_offset := Vector3(randf_range(-1, 1), 0.0, randf_range(-1, 1))
+			lateral_offset = lateral_offset.normalized() if lateral_offset.length_squared() > 0.001 else Vector3.FORWARD
+			lateral_offset *= randf_range(6.0, 14.0)
+			ship_position = Vector3(
+				clampf(ball_position.x + lateral_offset.x, -FIELD_HALF_X, FIELD_HALF_X),
+				randf_range(FIELD_MIN_Y, 4.0),
+				clampf(ball_position.z + lateral_offset.z, -FIELD_HALF_Z, FIELD_HALF_Z)
+			)
+			if _far_enough_from(ship_position, placed):
+				break
+		placed.append(ship_position)
 		var orientation := Basis.from_euler(Vector3(
 			randf_range(-0.4, 0.4), randf_range(-PI, PI), randf_range(-0.4, 0.4)
 		))
@@ -453,6 +476,10 @@ func _place_ball_near_goal() -> void:
 
 
 func _place_ships_random() -> void:
+	# Placed one at a time, resampling each against every position already
+	# placed this reset (see MIN_SHIP_SEPARATION) — otherwise a team_size > 1
+	# roster is sampled independently per ship and can spawn interpenetrating.
+	var placed: Array[Vector3] = []
 	for ship in ships:
 		# Inert opponents (opponent_mode=inert) stay parked at their arena
 		# spawn instead of drifting into the play area as a stray obstacle —
@@ -465,13 +492,17 @@ func _place_ships_random() -> void:
 			randf_range(-0.4, 0.4)
 		))
 		var velocity := _random_direction() * randf_range(0.0, MAX_RANDOM_SHIP_SPEED)
-		_place_body(ship, Transform3D(orientation, _random_position()), velocity, Vector3.ZERO)
+		var position := _random_position(placed)
+		placed.append(position)
+		_place_body(ship, Transform3D(orientation, position), velocity, Vector3.ZERO)
 
 
-func _random_position() -> Vector3:
+func _random_position(exclude: Array[Vector3] = []) -> Vector3:
 	# Resample anything too close to a corner curve or wall-base fillet (see
-	# CORNER_LIMIT / FILLET_CLEAR_Y); the violating region is a few percent
-	# of the volume, so 20 attempts effectively never fall through.
+	# CORNER_LIMIT / FILLET_CLEAR_Y), or too close to an already-placed ship
+	# this same reset (see MIN_SHIP_SEPARATION); the violating region is a
+	# few percent of the volume, so 20 attempts effectively never fall
+	# through even placing a full 5v5 roster one at a time.
 	var position := Vector3.ZERO
 	for _attempt in 20:
 		position = Vector3(
@@ -479,11 +510,18 @@ func _random_position() -> Vector3:
 			randf_range(FIELD_MIN_Y, FIELD_MAX_Y),
 			randf_range(-FIELD_HALF_Z, FIELD_HALF_Z)
 		)
-		if _spawn_position_clear(position):
+		if _spawn_position_clear(position) and _far_enough_from(position, exclude):
 			break
 	return position
 
 
+func _far_enough_from(position: Vector3, others: Array[Vector3]) -> bool:
+	for other in others:
+		if position.distance_squared_to(other) < MIN_SHIP_SEPARATION * MIN_SHIP_SEPARATION:
+			return false
+	return true
+
+
 func _spawn_position_clear(position: Vector3) -> bool:
 	if absf(position.x) + absf(position.z) > CORNER_LIMIT:
 		return false

Game/shaders/nebula_dust.gdshader

@@ -11,8 +11,8 @@ uniform float soft_fade_distance : hint_range(0.0, 5.0) = 1.0;
 // see ArenaBoundary.INNER_HALF_X/INNER_HALF_Z/INNER_HEIGHT. Dust is fully
 // hidden inside that box and fades in over arena_clear_distance beyond it,
 // so it reads as drifting around the station rather than through the pitch.
-uniform vec3 arena_half_extents = vec3(12.0, 6.0, 18.0);
-uniform vec3 arena_centre = vec3(0.0, 6.0, 0.0);
+uniform vec3 arena_half_extents = vec3(18.0, 9.0, 27.0);
+uniform vec3 arena_centre = vec3(0.0, 9.0, 0.0);
 uniform float arena_clear_distance : hint_range(0.0, 10.0) = 2.0;
 
 varying float v_flicker;

Game/tools/bake_arena_boundary.gd

@@ -0,0 +1,47 @@
+extends SceneTree
+
+# One-off bake: runs ArenaBoundary's collider generation once and commits the
+# result into objects/arena_boundary.tscn, so every arena load (and every
+# parallel headless training env) skips regenerating ~170 CollisionShape3D
+# nodes at runtime — ArenaBoundary._ready() already skips this itself once a
+# bake matching the current goal_mode exists (see bake_colliders).
+#
+# Safe to re-run any time a geometry constant changes (arena size, corner/
+# fillet radii, goal aperture, segment counts, etc.) — bake_colliders() clears
+# its own prior output first, so this replaces rather than duplicates:
+#   godot --headless --path Game --script res://tools/bake_arena_boundary.gd
+
+const ARENA_BOUNDARY_PATH := "res://objects/arena_boundary.tscn"
+
+
+func _initialize() -> void:
+	var packed: PackedScene = load(ARENA_BOUNDARY_PATH)
+	var instance := packed.instantiate()
+	instance.bake_colliders()
+	# PackedScene.pack() only serializes nodes whose `owner` is set to the
+	# scene root — newly created nodes have no owner by default, so without
+	# this, pack() silently produces a scene with none of the just-built
+	# colliders in it.
+	_set_owner_recursive(instance, instance)
+
+	var rebaked := PackedScene.new()
+	var pack_result := rebaked.pack(instance)
+	if pack_result != OK:
+		push_error("bake_arena_boundary: pack() failed with error %d" % pack_result)
+		quit(1)
+		return
+
+	var save_result := ResourceSaver.save(rebaked, ARENA_BOUNDARY_PATH)
+	if save_result != OK:
+		push_error("bake_arena_boundary: save() failed with error %d" % save_result)
+		quit(1)
+		return
+
+	print("bake_arena_boundary: baked colliders into %s" % ARENA_BOUNDARY_PATH)
+	quit()
+
+
+func _set_owner_recursive(node: Node, scene_root: Node) -> void:
+	for child in node.get_children():
+		child.owner = scene_root
+		_set_owner_recursive(child, scene_root)

TODO.md

@@ -10,18 +10,6 @@ The training pipeline is built — see `TRAINING.md` (self-play PPO via the vend
 - [ ] Frozen-opponent league: train the live policy against a *pool* of past exported checkpoints, sampled per-episode (today's `--opponent-mode=frozen` only supports one fixed model per run) to prevent self-play strategy collapse on long runs.
 - [ ] Richer state setter / curriculum: aerial states, wall plays, rebound scenarios as skill grows (beyond the score/defend/draw staging already in place).
 
-## Correctness
-
-Bugs found in an adversarial review. None are gameplay- or physics-affecting, so all are safe to land against the current `Game/bots/` checkpoints.
-
-- [ ] Goal scoring volume (3.5 x 1.5, `objects/goal.tscn`) is smaller than the drawn mouth (3.7 x 1.65, `ArenaBoundary.GOAL_APERTURE_*`) — a ball crossing the visible edge doesn't score. Derive the aperture constants from the goal's collision shape, the way `goal.gd:53` already measures its own visuals.
-- [ ] Delete the duplicate 1 MB texture — `assets/textures/planet_surface.png` and `assets/models/nebula_planet_planet_surface.png` are byte-identical.
-
-## Performance
-
-- [ ] Measure `nebula_dust.gdshader`'s per-fragment depth-texture sample across 500 large soft billboards before adding more particle work.
-- [ ] Bake `ArenaBoundary`'s ~160 runtime-generated `CollisionShape3D` nodes into the scene. Costs a load hitch on every arena entry and repeats in every parallel headless training env. **Blocked on the trained-bot decision below** — `arena_boundary.gd:235` notes this geometry is what the shipped policies were fitted against, so the bake must be verified byte-identical.
-
 ## Presentation / AAA polish
 
 The largest gap between this and a AAA-feeling product is presentation, not code. Sequenced after the above for pragmatic reasons, but this is the highest impact per hour.
@@ -37,15 +25,6 @@ The largest gap between this and a AAA-feeling product is presentation, not code
 - [ ] Custom font + a real `Theme` resource for the HUD. The procedural instruments are well-engineered, but `ThemeDB.fallback_font` at 10-13 px reads as a debug overlay.
 - [ ] Post-processing beyond glow: DoF, motion blur, vignette, chromatic aberration on turbo.
 
-## Open decision — trained-bot compatibility
-
-Four items collide with the checkpoints in `Game/bots/`. Decide the policy before scheduling any of them; everything in Correctness and DRY above is safe either way.
-
-- [ ] **Per-tick drag** (`ship.gd`): `state.linear_velocity *= drag_coefficient` and `angular_velocity *= 0.9` aren't delta-scaled, and `project.godot` never pins `physics/common/physics_ticks_per_second`. Correct at 60 Hz, silently different at any other rate. Zero-risk option: pin the tick rate to 60 and document the dependency. Correct-but-breaking option: delta-scale it and retrain.
-- [ ] **Goal aperture** — cutting a real opening in the end walls so the ball visibly enters the net changes collision geometry the policies were fitted against. Today the walls are solid and the pocket/net are unreachable decoration.
-- [ ] **Collider bake** (see Performance above) — safe only if byte-identical to the current generated output.
-- [ ] **Beyond 1v1** — `ai_ship_controller.gd` takes the first non-self ship as "the opponent" and `ship_observations.gd` has room for exactly one. The observation space is the hardest thing to change later, so decide whether 2v2/3v3 is in scope before more training time is spent.
-
 ## Multiplayer (long term)
 
 - [ ] `RemoteShipController extends ShipController` — feeds replicated `ShipAction`s from a network peer into the local ship simulation.

tools/textures/gen_planet_surface.py

@@ -1,11 +1,11 @@
-"""Generates Game/assets/textures/planet_surface.png (and the byte-identical
-Game/assets/models/nebula_planet_planet_surface.png sidecar that actually feeds
-the live nebula_planet.glb material -- Godot's glTF importer extracted the
-embedded image there at import time, so the imported scene references that
-external file, not the glb's internal binary): a 2048x1024 equirectangular
-decorative planet with latitude bands, storm vortices, and a lit/unlit
-terminator, via layered FFT/domain-warped noise in the same style as
-gen_nebula_sky.py (helpers duplicated here to keep both scripts standalone).
+"""Generates Game/assets/models/nebula_planet_planet_surface.png, the sidecar
+that actually feeds the live nebula_planet.glb material -- Godot's glTF
+importer extracted the embedded image there at import time, so the imported
+scene references that external file, not the glb's internal binary. A
+2048x1024 equirectangular decorative planet with latitude bands, storm
+vortices, and a lit/unlit terminator, via layered FFT/domain-warped noise in
+the same style as gen_nebula_sky.py (helpers duplicated here to keep both
+scripts standalone).
 """
 
 from pathlib import Path
@@ -178,12 +178,8 @@ color = np.clip(color, 0.0, 1.0)
 
 print("saving planet surface...")
 root = Path(__file__).resolve().parents[2]
-out_paths = [
-    root / "Game" / "assets" / "textures" / "planet_surface.png",
-    root / "Game" / "assets" / "models" / "nebula_planet_planet_surface.png",
-]
+out_path = root / "Game" / "assets" / "models" / "nebula_planet_planet_surface.png"
 img = Image.fromarray((color * 255).astype(np.uint8), "RGB")
-for p in out_paths:
-    img.save(p)
-    print("saved:", p)
+img.save(out_path)
+print("saved:", out_path)
 print("done")