diff --git a/src/game/engine/scenes/headless/player_api_main.gd b/src/game/engine/scenes/headless/player_api_main.gd
index 7f1cc8a1..0470be20 100644
--- a/src/game/engine/scenes/headless/player_api_main.gd
+++ b/src/game/engine/scenes/headless/player_api_main.gd
@@ -23,6 +23,7 @@ extends Node
 
 var _api: RefCounted = null
 var _player_slot: int = 0
+var _player_slots: Array[int] = []  # Stage 4 — slots driven externally.
 var _omniscient: bool = false
 var _log_path: String = ""
 var _shutdown: bool = false
@@ -30,6 +31,27 @@ var _shutdown: bool = false
 
 func _ready() -> void:
 	_player_slot = _env_int("CP_PLAYER_SLOT", 0)
+	# Stage 4 (multi-slot adapter) — `CP_PLAYER_SLOTS="0,1,2"` lets one
+	# harness process drive several slots (e.g. all 5 learned slots in a
+	# 5v5 FFA). Per-request `slot` field on view/act picks which slot
+	# this call targets. Empty / unset → fall through to single-slot
+	# mode using `CP_PLAYER_SLOT`.
+	_player_slots = []
+	var slots_env: String = OS.get_environment("CP_PLAYER_SLOTS")
+	if not slots_env.is_empty():
+		for piece: String in slots_env.split(","):
+			var trimmed: String = piece.strip_edges()
+			if trimmed.is_empty():
+				continue
+			var n: int = int(trimmed)
+			if not _player_slots.has(n):
+				_player_slots.append(n)
+	if _player_slots.is_empty():
+		_player_slots = [_player_slot]
+	else:
+		# First entry in the list is the back-compat default for
+		# requests that omit the `slot` field.
+		_player_slot = _player_slots[0]
 	_omniscient = _env_bool("CP_OMNISCIENT", false)
 	_log_path = OS.get_environment("CP_LOG_FILE")
 
@@ -149,7 +171,7 @@ func _hydrate_player_api(num_players: int) -> void:
 	# only reads the file bytes and picks the clan id per slot — no JSON
 	# parsing here. Deterministic slot→clan mapping: slot index modulo
 	# the clan list (sorted by id for stable ordering across runs).
-	_apply_ai_personalities(gs, num_players)
+	_apply_ai_assignments(gs, num_players)
 
 	var json: String = String(gs.to_json())
 	if json.is_empty() or json == "{}":
@@ -299,12 +321,20 @@ func _apply_ai_catalogs() -> void:
 	})
 
 
-func _apply_ai_personalities(gs: RefCounted, num_players: int) -> void:
-	## p2-68 final wave. Read `ai_personalities.json` once and hand the
-	## raw bytes plus a per-slot clan id to `GdGameState::set_player_personality_json`.
-	## Slot 0 = Claude — skipped. Slots 1..N-1 cycle through the sorted
+func _apply_ai_assignments(gs: RefCounted, num_players: int) -> void:
+	## Stage 3 (mod system) — per-AI-slot assignment of BOTH personality
+	## (`scoring_weights` / clan id) AND `controller_id` (which
+	## `AiController` impl decides this slot's turn).
+	##
+	## Personality: read `ai_personalities.json` once and hand the raw
+	## bytes plus a per-slot clan id to `GdGameState::set_player_personality_json`.
+	## Slot 0 = Claude — skipped. Other slots cycle through the sorted
 	## clan id list so a 2-player game always pairs Claude vs `blackhammer`
 	## (alphabetically first), a 6-player game uses every clan exactly once.
+	##
+	## Controller: per-slot id from `CP_PLAYER_CONTROLLERS` (comma list,
+	## indexed by AI position) or fall through to `scripted:default`.
+	## Stamped via `GdGameState::set_player_controller`.
 	const PERSONALITIES_PATH: String = "res://public/games/age-of-dwarves/data/ai_personalities.json"
 	# Canonical project-resource path — same constant `how_to_play.gd` and
 	# `loading_screen.gd` use. Works under editor + flatpak headless.
@@ -331,6 +361,15 @@ func _apply_ai_personalities(gs: RefCounted, num_players: int) -> void:
 	if clan_ids.is_empty():
 		_emit_protocol_error("ai_personalities.json has no clans")
 		return
+	# Per-slot controller override list. Format: comma-separated ids,
+	# one entry per AI slot in slot order (excluding `_player_slot`).
+	# Empty / missing entries default to `scripted:default`.
+	#   CP_PLAYER_CONTROLLERS="learned:duel-v1b,scripted:default,..."
+	var controllers_env: String = _env_or("CP_PLAYER_CONTROLLERS", "")
+	var controller_overrides: Array[String] = []
+	if not controllers_env.is_empty():
+		for piece: String in controllers_env.split(","):
+			controller_overrides.append(piece.strip_edges())
 	# Deterministic slot→clan mapping: count AI slots in slot order and
 	# assign clan_ids[ai_index % clan_count]. Stable across runs.
 	var ai_index: int = 0
@@ -338,12 +377,22 @@ func _apply_ai_personalities(gs: RefCounted, num_players: int) -> void:
 		if slot == _player_slot:
 			continue
 		var clan_id: String = clan_ids[ai_index % clan_ids.size()]
+		var controller_id: String = "scripted:default"
+		if ai_index < controller_overrides.size():
+			var override: String = controller_overrides[ai_index]
+			if not override.is_empty():
+				controller_id = override
 		ai_index += 1
 		var ok: bool = bool(gs.set_player_personality_json(slot, clan_id, json_text))
 		if not ok:
 			_emit_protocol_error("set_player_personality_json failed slot=%d clan=%s" % [slot, clan_id])
 		else:
 			_emit_event("ai_personality_assigned", {"slot": slot, "clan_id": clan_id})
+		var ok_ctrl: bool = bool(gs.set_player_controller(slot, controller_id))
+		if not ok_ctrl:
+			_emit_protocol_error("set_player_controller failed slot=%d controller=%s" % [slot, controller_id])
+		else:
+			_emit_event("ai_controller_assigned", {"slot": slot, "controller_id": controller_id})
 
 
 func _scan_land_tiles(grid: RefCounted, w: int, h: int) -> Array[Vector2i]:
@@ -416,9 +465,15 @@ func _handle_request(req: Dictionary) -> void:
 	var rtype: String = String(req.get("type", ""))
 	var rid_int: int = int(req.get("id", -1))
 	var has_id: bool = req.has("id") and req.get("id") != null
+	# Stage 4 — per-request `slot` field picks which player this view /
+	# act targets. Missing → fall through to `_player_slot` (the first
+	# entry of `_player_slots` or the legacy single-slot value).
+	var target_slot: int = _player_slot
+	if req.has("slot") and req.get("slot") != null:
+		target_slot = int(req.get("slot"))
 	match rtype:
 		"view":
-			var view_json: String = String(_api.view_json(_player_slot))
+			var view_json: String = String(_api.view_json(target_slot))
 			_emit_response_with_view(rid_int, has_id, view_json)
 		"act":
 			var action_payload: Dictionary = req.get("action", {}) as Dictionary
@@ -427,7 +482,7 @@ func _handle_request(req: Dictionary) -> void:
 				return
 			var action_json: String = JSON.stringify(action_payload)
 			var envelope_str: String = String(
-				_api.apply_action_json(_player_slot, action_json)
+				_api.apply_action_json(target_slot, action_json)
 			)
 			# api wrapper already emits a full ok/err envelope — splice
 			# in the request id and forward as the response body.