feat: report ATL problems only for used transforms; animate moving images

- Unsupported ATL constructs in a transform now block the import only when the
  transform is used (at clause, another transform, even before its definition).
  Stock screens.rpy transforms for unused screens no longer fail games
- image blocks with one picture plus linear/ease/parallel/repeat keep their
  animation (image-level ATL); the renderer also starts it
- Python: skip @gui.variant/@renpy.variant functions (inactive variants), treat
  @renpy.pure as transparent, read renpy.store.x as x
- Accept renpy.transition, end_replay, block_rollback and music set_pause/set_pan
  as presentation-only no-ops, and implement them in the player (set_pause and
  set_pan were allowed by the converter but missing at runtime)
- Skip the 0x52-URM add-on directory (in-game console / save editor) when
  parsing scripts and media
- Tests for lazy ATL warnings, moving images and variants

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

backend/tests/test_compatibility.py

@@ -102,9 +102,14 @@ def test_renpy_atl_animation_becomes_a_timeline_not_a_static_pose():
 def test_renpy_atl_constructs_without_a_runtime_are_still_rejected():
     for body in ("function slide", "time 1.0:\n        xalign 1.0", "matrixcolor TintMatrix('#f00')",
                  "contains:\n        'a.png'"):
-        data = script(f'transform odd:\n    {body}\nlabel start:\n    "Hi"')
+        unused = script(f'transform odd:\n    {body}\nlabel start:\n    "Hi"')
+        require_supported_scripts(unused)  # nothing shows it, so it cannot break the game
+        used = script(f'transform odd:\n    {body}\nlabel start:\n    show eileen at odd\n    "Hi"')
         with pytest.raises(CompatibilityError, match="ATL"):
-            require_supported_scripts(data)
+            require_supported_scripts(used)
+        early = script(f'label start:\n    show eileen at odd\n    "Hi"\ntransform odd:\n    {body}\n')
+        with pytest.raises(CompatibilityError, match="ATL"):  # used before it is defined
+            require_supported_scripts(early)
 
 
 def test_renpy_atl_groups_events_and_named_transforms():

backend/tests/test_converter.py

@@ -164,3 +164,34 @@ def test_atl_frames_layeredimage_and_channels():
                          "img": {"ref": "eileen_face_happy"}}
     assert layers[2]["img"] == {"file": "sad.png"}
     assert d.channels["amb"] == {"mixer": "sfx", "loop": True}
+
+
+def test_moving_image_keeps_its_animation():
+    d = parse('image spin:\n    "mark.png"\n    xalign 0.5\n    linear 0 rotate 0\n    linear 4 rotate -360\n    repeat\n')
+    image = d.images["spin"]
+    assert image["file"] == "mark.png"
+    spec = image["at"][0]
+    assert spec["props"] == {"xalign": 0.5}
+    assert spec["atl"]["repeat"] is True and spec["atl"]["steps"][-1]["props"] == {"rotate": -360.0}
+    assert not d.blockers
+
+
+def test_unused_transforms_with_unsupported_atl_do_not_block():
+    d = parse("transform spinner(delay, cycle):\n    function renpy.display.layout.example\nlabel start:\n    'Hi'\n")
+    assert not d.blockers
+
+
+def test_gui_variants_and_renpy_store_are_understood():
+    d = parse(
+        "init python:\n"
+        "    @gui.variant\n"
+        "    def small():\n"
+        "        gui.text_size = 30\n"
+        "    @renpy.pure\n"
+        "    def twice(x):\n"
+        "        return x * 2\n"
+        "    renpy.store.seen.append(1)\n")
+    assert [s["op"] for s in d.init_code] == ["def", "eval"]
+    assert d.init_code[0]["decos"] == [] and d.init_code[0]["name"] == "twice"
+    assert d.init_code[1]["e"]["f"]["o"] == {"k": "name", "id": "seen"}
+    assert not d.blockers