Add Phase 4 Final Bugs Specification and Tests

- Introduced a new architecture specification for Phase 4 final bugs, detailing scope, decisions, runtime data contracts, action roles, execution lanes, speech ownership, and signal flow.
- Implemented changes in `scripts/action_registry.gd`, `scripts/action_editor.gd`, `scripts/sandbox_stage.gd`, `scripts/stage_gizmos.gd`, `scripts/stickman_factory.gd`, and `scripts/stickman_rig.gd` to address identified bugs.
- Created a new test suite `tests/test_phase4_final_bugs.gd` to validate the implementation, covering action roles, grid snapping, prop manipulation, reactive runtime lane, spawn pose preservation, and more.
- Added a unique identifier for the test file to ensure proper tracking and management.

scripts/stage_gizmos.gd

@@ -22,6 +22,8 @@ enum Handle { NONE, TRANSLATE, ROTATE }
 # ---------------------------------------------------------------------------
 
 signal transform_committed(nodes: Array[Node2D])
+signal transform_started(nodes: Array[Node2D])
+signal transform_updated(nodes: Array[Node2D])
 
 # ---------------------------------------------------------------------------
 # Style constants (screen-space px; divided by zoom for world-space drawing)
@@ -53,6 +55,8 @@ var _hovered: Node2D = null
 var _dragging: Handle = Handle.NONE
 var _drag_last: Vector2 = Vector2.ZERO
 var _drag_anchor: Node2D = null
+var _translate_drag_origin: Vector2 = Vector2.ZERO
+var _translate_start_positions: Dictionary = {}
 var _rotate_start_rotation: float = 0.0
 var _rotate_start_angle: float = 0.0
 var _rotate_center: Vector2 = Vector2.ZERO
@@ -78,6 +82,10 @@ func set_enabled(enabled: bool) -> void:
 	queue_redraw()
 
 
+func set_snap_size(size: float) -> void:
+	snap_size = maxf(size, 0.0)
+
+
 func set_box_rect(rect: Rect2) -> void:
 	_box_rect = rect
 	queue_redraw()
@@ -105,31 +113,39 @@ func begin_drag(world_pos: Vector2) -> void:
 		_rotate_center = STAGE_SELECTION.get_world_aabb(_targets[0]).get_center()
 		_rotate_start_rotation = _targets[0].global_rotation
 		_rotate_start_angle = (world_pos - _rotate_center).angle()
+		transform_started.emit(_targets.duplicate())
 
 
 ## Begins a translate drag anchored on `node` (used when an object body is
 ## clicked). The drag moves the whole current selection (`_targets`); if `node`
 ## is not currently selected, the drag targets just `node`.
 func begin_translate_drag(node: Node2D, world_pos: Vector2) -> void:
+	if node == null or not is_instance_valid(node):
+		return
 	_drag_anchor = node
 	if not _targets.has(node):
 		_targets = [node]
 	_dragging = Handle.TRANSLATE
 	_drag_last = world_pos
+	_translate_drag_origin = world_pos
+	_translate_start_positions.clear()
+	for target: Node2D in _targets:
+		if target != null and is_instance_valid(target):
+			_translate_start_positions[target] = target.global_position
+	transform_started.emit(_targets.duplicate())
 
 
 func drag_to(world_pos: Vector2) -> void:
 	if _dragging == Handle.NONE or _targets.is_empty():
 		return
-	var delta := world_pos - _drag_last
 	if _dragging == Handle.TRANSLATE:
-		var actual := delta
+		var actual := world_pos - _translate_drag_origin
 		if snap_size > 0.0 and _drag_anchor != null and is_instance_valid(_drag_anchor):
-			var old := _drag_anchor.global_position
-			actual = _snap(old + delta) - old
+			var anchor_start: Vector2 = _translate_start_positions.get(_drag_anchor, _drag_anchor.global_position)
+			actual = _snap(anchor_start + actual) - anchor_start
 		for node: Node2D in _targets:
-			if is_instance_valid(node):
-				node.global_position += actual
+			if is_instance_valid(node) and _translate_start_positions.has(node):
+				node.global_position = (_translate_start_positions[node] as Vector2) + actual
 	elif _dragging == Handle.ROTATE:
 		if _targets.size() == 1 and is_instance_valid(_targets[0]):
 			var target := _targets[0]
@@ -140,6 +156,7 @@ func drag_to(world_pos: Vector2) -> void:
 				new_rotation = snappedf(new_rotation, deg_to_rad(15.0))
 			target.global_rotation = new_rotation
 	_drag_last = world_pos
+	transform_updated.emit(_targets.duplicate())
 	queue_redraw()
 
 
@@ -148,6 +165,7 @@ func end_drag() -> void:
 		transform_committed.emit(_targets.duplicate())
 	_dragging = Handle.NONE
 	_drag_anchor = null
+	_translate_start_positions.clear()
 
 
 func is_dragging() -> bool:
@@ -194,4 +212,6 @@ func _rotate_ring_radius(rect: Rect2) -> float:
 
 
 func _snap(v: Vector2) -> Vector2:
+	if snap_size <= 0.0:
+		return v
 	return Vector2(roundf(v.x / snap_size) * snap_size, roundf(v.y / snap_size) * snap_size)