feat: Integrate custom prop library and sandbox functionality

- Added support for custom props in the sandbox, including loading, saving, and rendering.
- Implemented `PropLibrary` for managing custom prop entries and scanning for `.prop` files.
- Introduced `PropVisuals` for shared visual and collision representation of custom props.
- Enhanced `StageSpawner` to handle spawning of custom props with layered visuals and collision hulls.
- Created `MissingPropPlaceholder` to manage missing custom props during scene reloads.
- Updated thumbnail generation to support custom props with unique keys based on file paths.
- Added tests for custom prop lifecycle, authored visual values, and missing prop handling.
- Refactored existing code to accommodate new prop functionalities and ensure backward compatibility.

scripts/sandbox_stage.gd

@@ -39,6 +39,7 @@ const RULE_EDITOR := preload("res://scenes/rule_editor.tscn")
 const WAYPOINT_CONTEXT := preload("res://scripts/waypoint_context.gd")
 const STAGE_SCENE_IO := preload("res://scripts/stage_scene_io.gd")
 const MISSING_STICKMAN_PLACEHOLDER := preload("res://scripts/missing_stickman_placeholder.gd")
+const MISSING_PROP_PLACEHOLDER := preload("res://scripts/missing_prop_placeholder.gd")
 
 # ---------------------------------------------------------------------------
 # Enums
@@ -1272,7 +1273,7 @@ func _collect_scene_data(is_autosave: bool = false) -> Dictionary:
 		var n := node as Node2D
 		var type := ""
 		if n is TerrainBlock: type = "terrain"
-		elif n is PropBlock: type = "prop"
+		elif n is PropBlock or n.get_script() == MISSING_PROP_PLACEHOLDER: type = "prop"
 		elif n is STICKMAN_RIG or n.get_script() == MISSING_STICKMAN_PLACEHOLDER: type = "stickman"
 		elif n is TriggerArea: type = "area"
 		else: continue
@@ -1286,6 +1287,9 @@ func _collect_scene_data(is_autosave: bool = false) -> Dictionary:
 		if type == "terrain":
 			entry["asset_id"] = (n as TerrainBlock).spawn_id
 			entry["scale"] = STAGE_SCENE_IO.vector_to_data(n.scale)
+		elif type == "prop" and n.get_script() == MISSING_PROP_PLACEHOLDER:
+			entry = (n.get("original_entry") as Dictionary).duplicate(true)
+			entry["file_id"] = file_id; entry["type"] = "prop"; entry["position"] = STAGE_SCENE_IO.vector_to_data(pos); entry["rotation"] = rot; entry["scale"] = STAGE_SCENE_IO.vector_to_data(n.scale)
 		elif type == "prop":
 			var prop := n as PropBlock
 			entry["asset_id"] = prop.spawn_id
@@ -1355,7 +1359,11 @@ func _apply_scene_data(data: Dictionary, source_path: String, is_recovery: bool)
 		var node: Node2D = null
 		match type:
 			"terrain": node = _spawner.spawn_terrain_asset(String(entry.get("asset_id", "")), pos)
-			"prop": node = _spawner.spawn_prop_asset(String(entry.get("asset_id", "")), pos)
+			"prop":
+				node = _spawner.spawn_prop_asset(String(entry.get("asset_id", "")), pos)
+				if node == null and PROP_LIBRARY.is_custom_path(String(entry.get("asset_id", ""))):
+					var prop_placeholder: Node2D = MISSING_PROP_PLACEHOLDER.new() as Node2D
+					prop_placeholder.configure(entry); prop_placeholder.position = pos; _world.add_child(prop_placeholder); node = prop_placeholder
 			"area": node = _spawner.spawn_area(pos)
 			"stickman":
 				node = _spawner.spawn_stickman_asset(String(entry.get("stk_path", "")), pos)
@@ -2408,7 +2416,7 @@ func _open_selector(kind: String) -> void:
 		if not entries.is_empty() and _stickman_library.find_by_path(_spawner.get_selected_stickman_path()).is_empty():
 			_spawner.selected_stickman_path = String(entries[0]["path"])
 	else:
-		entries = PROP_LIBRARY.get_entries()
+		entries = PROP_LIBRARY.scan()
 	if kind == "stickman" and entries.size() == 1:
 		_on_asset_selected(entries[0])
 		return
@@ -2449,18 +2457,29 @@ func _on_selector_cancelled() -> void:
 
 func _on_browse_requested() -> void:
 	if _browse_dialog != null:
+		if _selector_kind == "prop":
+			_browse_dialog.title = "Open .prop"
+			_browse_dialog.filters = PackedStringArray(["*.prop ; Prop Files"])
+		else:
+			_browse_dialog.title = "Open .stk"
+			_browse_dialog.filters = PackedStringArray(["*.stk ; Stickman Files"])
 		_browse_dialog.popup_centered()
 
 
 func _on_browse_file_selected(path: String) -> void:
-	var entry := _stickman_library.make_entry(path)
+	var entry: Dictionary = PROP_LIBRARY.make_custom_entry(path) if _selector_kind == "prop" else _stickman_library.make_entry(path)
 	if entry.is_empty():
-		_show_toast("Could not load stickman: " + path)
+		_show_toast("Could not load %s: %s" % [_selector_kind, path])
 		return
 	_on_asset_selected(entry)
 
 
 func _on_refresh_requested() -> void:
+	if _selector_kind == "prop":
+		var prop_entries: Array[Dictionary] = PROP_LIBRARY.scan()
+		_selector.set_entries(prop_entries)
+		_load_or_enqueue_thumbnails("prop", prop_entries)
+		return
 	var entries: Array[Dictionary] = _stickman_library.scan()
 	if not entries.is_empty() and _stickman_library.find_by_path(_spawner.get_selected_stickman_path()).is_empty():
 		_spawner.selected_stickman_path = String(entries[0]["path"])
@@ -2485,7 +2504,7 @@ func _load_or_enqueue_thumbnails(kind: String, entries: Array[Dictionary]) -> vo
 				_thumbnail_queue.append({ "kind": kind, "entry": entry, "key": key, "cache_path": png, "generation": generation })
 		else:
 			var id := String(entry.get("id", ""))
-			var png := _thumbnail_cache.prop_png(id)
+			var png := _thumbnail_cache.prop_file_png(id) if bool(entry.get("is_custom", false)) else _thumbnail_cache.prop_png(id)
 			var tex := _thumbnail_cache.get_texture(png)
 			if tex != null:
 				if tex != null and _selector != null:
@@ -2509,11 +2528,15 @@ func _drain_thumbnail_queue() -> void:
 		if tex != null:
 			_thumbnail_cache.store_texture(String(job.get("cache_path", _thumbnail_cache.stickman_png(key))), tex)
 	else:
-		var payload: Dictionary = entry["payload"]
-		var preset: int = int(entry["material_preset"])
-		tex = await _prop_thumb.render(payload, preset)
+		if bool(entry.get("is_custom", false)):
+			tex = await _prop_thumb.render_shapes(entry.get("shapes", []) as Array[Dictionary])
+		else:
+			var payload: Dictionary = entry["payload"]
+			var preset: int = int(entry["material_preset"])
+			tex = await _prop_thumb.render(payload, preset)
 		if tex != null:
-			_thumbnail_cache.store_texture(String(job.get("cache_path", _thumbnail_cache.prop_png(String(entry["id"])))), tex)
+			var fallback := _thumbnail_cache.prop_file_png(String(entry["id"])) if bool(entry.get("is_custom", false)) else _thumbnail_cache.prop_png(String(entry["id"]))
+			_thumbnail_cache.store_texture(String(job.get("cache_path", fallback)), tex)
 	_thumbnail_busy = false
 	if _selector != null and _selector_open and int(job.get("generation", -1)) == _thumbnail_generation and tex != null:
 		_selector.set_thumbnail(entry, tex)