feat(@projects/@magic-civilization): ✨ add json keyword-based capability system

Co-Authored-By: Lilith Autocommit <noreply@atlilith.com>

src/game/engine/scenes/hud/action_button.tscn

@@ -0,0 +1,5 @@
+[gd_scene format=3 uid="uid://a1c2t3i4o5n6b"]
+
+[node name="ActionButton" type="Button"]
+custom_minimum_size = Vector2(0, 28)
+size_flags_horizontal = 3

src/game/engine/src/entities/unit.gd

@@ -32,9 +32,11 @@ var unit_type: String = ""
 var domain: String = "land"
 
 # ── Capability flags ─────────────────────────────────────────────────
-## True if this unit can found cities (derived from "found_city" keyword).
+## Keywords from unit JSON (replaces legacy flags/can_found_city/can_build_improvements).
+var keywords: Array[String] = []
+## True if this unit can found cities — derived from "founder" keyword.
 var can_found_city: bool = false
-## True if this unit can build tile improvements (derived from "build" keyword).
+## True if this unit can build tile improvements — derived from "worker" keyword.
 var can_build_improvements: bool = false
 
 # ── Position & ownership ──────────────────────────────────────────────
@@ -143,16 +145,12 @@ func _populate_from_data() -> void:
 	domain = String(data.get("domain", "land"))
 	if display_name.is_empty():
 		display_name = data.get("name", unit_id.capitalize())
-	var is_founder: bool = (
-		unit_id.contains("founder")
-	)
-	can_found_city = data.get("can_found_city", is_founder)
-	var is_builder: bool = (
-		unit_id.contains("worker") or unit_id.contains("engineer")
-	)
-	can_build_improvements = data.get(
-		"can_build_improvements", is_builder
-	)
+	var raw_keywords: Array = data.get("keywords", [])
+	keywords.clear()
+	for k: Variant in raw_keywords:
+		keywords.append(String(k))
+	can_found_city = "founder" in keywords
+	can_build_improvements = "worker" in keywords
 
 
 # ── Per-turn refresh (called by turn_processor.gd) ────────────────────
@@ -261,18 +259,47 @@ func _combat_type() -> String:
 	return data.get("combat_type", "")
 
 
-## List of keyword strings for this unit, sourced from JSON unit data.
-## Returns an empty array for units whose `unit_id` has no DataLoader entry.
-func get_keywords() -> Array:
-	if unit_id.is_empty():
-		return []
-	var data: Dictionary = DataLoader.get_unit(unit_id)
-	return data.get("keywords", [])
+## List of keyword strings for this unit (populated from JSON at init).
+func get_keywords() -> Array[String]:
+	return keywords
 
 
-## True if this unit has `keyword` in its JSON keyword list.
+## True if this unit has `keyword` in its keyword list.
 func has_keyword(keyword: String) -> bool:
-	return keyword in get_keywords()
+	return keyword in keywords
+
+
+## Space-separated keywords string for the GdUnitActions bridge.
+func get_keywords_str() -> String:
+	return " ".join(keywords)
+
+
+## Return the legal actions for this unit's current state via GdUnitActions.
+## Each entry is a Dictionary {kind: String, enabled: bool, disabled_reason: String}.
+func get_legal_actions() -> Array[Dictionary]:
+	if not ClassDB.class_exists("GdUnitActions"):
+		return []
+	var bridge: RefCounted = ClassDB.instantiate("GdUnitActions") as RefCounted
+	return bridge.legal_actions_for(
+		unit_type,
+		get_keywords_str(),
+		movement_remaining > 0,
+		is_fortified
+	)
+
+
+## Returns true if `kind` (e.g. "fortify") is a legal enabled action right now.
+func can_invoke_action(kind: String) -> bool:
+	if not ClassDB.class_exists("GdUnitActions"):
+		return false
+	var bridge: RefCounted = ClassDB.instantiate("GdUnitActions") as RefCounted
+	return bridge.can_invoke(
+		unit_type,
+		get_keywords_str(),
+		movement_remaining > 0,
+		is_fortified,
+		kind
+	)
 
 
 # ── Movement / damage / healing helpers ───────────────────────────────

src/simulator/crates/mc-ai/src/tactical/movement.rs

@@ -876,9 +876,13 @@ mod tests {
             vec![-1, 0],
         );
         let actions = decide_movement(&state(0, vec![me, enemy]), &weights(), &mut rng());
+        // Registry integration: sole garrison defender with no movement target
+        // now fortifies in place rather than idling (Action::Fortify sourced
+        // from legal_actions).
+        assert_eq!(actions.len(), 1, "expected one action (Fortify), got {actions:?}");
         assert!(
-            actions.is_empty(),
-            "sole garrison defender should hold, got {actions:?}"
+            matches!(actions[0], Action::Fortify { .. }),
+            "sole garrison defender should fortify, got {actions:?}"
         );
     }