feat: conditional "at" transforms in screens and comma-separated ATL statements

`frame at (a if cond else b)` is kept as a choice that the player resolves each time the screen is
drawn. An ATL line splits at top-level commas into separate statements, so `zoom 1.2, 0.2` is a zoom
followed by a 0.2s pause, as Ren'Py compiles it (two-value properties such as `pos 0.5, 0.5` stay
whole). The inert events deselected/unselected, which Ren'Py never sends, are accepted. With the
build profile for The Only Doe 0.05 the game now passes the strict script check.

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

backend/app/converter/atl.py

@@ -52,7 +52,9 @@ NAMED_POSITIONS = {
     "topright": {"xpos": 1.0, "xanchor": 1.0, "ypos": 0.0, "yanchor": 0.0},
 }
 EVENTS = {"show", "hide", "replace", "replaced", "start", "update", "appear", "default", "hover", "idle",
-          "selected_hover", "selected_idle", "insensitive", "selected_insensitive", "selected"}
+          "selected_hover", "selected_idle", "insensitive", "selected_insensitive", "selected",
+          # Ren'Py itself never sends these (its selected states are the selected_* ones): the handler is inert
+          "deselected", "unselected"}
 
 
 GLUED_NUMBER = re.compile(r"^(\d+(?:\.\d*)?|\.\d+)([A-Za-z_]\w*)$")
@@ -102,6 +104,40 @@ def _split(text: str) -> list[str]:
     return out
 
 
+#: properties that take two numbers; `pos 0.5, 0.5` stays one statement
+TWO_VALUE = {"pos", "anchor", "align", "offset", "around", "size", "crop", "xysize", "xycenter", "alignaround"}
+
+
+def statements(text: str) -> list[str]:
+    """Split an ATL line at commas outside brackets and quotes: `zoom 1.2, 0.2` is `zoom 1.2` then a pause."""
+    pieces, cur, depth, quote = [], [], 0, ""
+    for ch in text:
+        if quote:
+            quote = "" if ch == quote else quote
+        elif ch in "\"'":
+            quote = ch
+        elif ch in "([{":
+            depth += 1
+        elif ch in ")]}":
+            depth -= 1
+        elif ch == "," and depth == 0:
+            pieces.append("".join(cur).strip())
+            cur = []
+            continue
+        cur.append(ch)
+    pieces.append("".join(cur).strip())
+    merged: list[str] = []
+    for piece in pieces:
+        if not piece:
+            continue
+        previous = merged[-1].split() if merged else []
+        if len(previous) == 2 and previous[0] in TWO_VALUE and len(piece.split()) == 1:
+            merged[-1] = f"{merged[-1]} {piece}"
+        else:
+            merged.append(piece)
+    return merged
+
+
 class AtlParser:
     def __init__(self, warn: Callable[[str, Line], None], is_static: Callable[[str], dict | None],
                  on_use: Callable[[str], None] = lambda name: None,
@@ -188,7 +224,19 @@ class AtlParser:
 
     # --- block ----------------------------------------------------------------------
 
+    def expand(self, lines: list[Line]) -> list[Line]:
+        """Lines holding several comma-separated statements become one line per statement."""
+        out: list[Line] = []
+        for line in lines:
+            pieces = statements(line.text.strip()) if not line.block and "," in line.text else []
+            if len(pieces) > 1:
+                out.extend(Line(piece, line.lineno, line.indent, line.physical) for piece in pieces)
+            else:
+                out.append(line)
+        return out
+
     def block(self, lines: list[Line]) -> Block:
+        lines = self.expand(lines)
         steps: list[dict[str, Any]] = []
         repeat: Any = None
         i = 0

backend/app/converter/screens.py

@@ -401,6 +401,21 @@ class ScreenParser:
             spec["atl"] = animation
         props["at"] = [*props.get("at", []), spec]
 
+    def at_ref(self, source: str, line: Line) -> Node:
+        """One `at` entry; `(a if cond else b)` picks a transform while the screen is shown."""
+        text = source.strip()
+        if text.startswith("(") and text.endswith(")"):
+            try:
+                tree = ast.parse(text, mode="eval").body
+            except SyntaxError:
+                tree = None
+            if isinstance(tree, ast.IfExp):
+                cond = self.expr(ast.unparse(tree.test), line)
+                if cond is not None:
+                    return {"choose": {"c": cond, "then": self.at_ref(ast.unparse(tree.body), line),
+                                       "else": self.at_ref(ast.unparse(tree.orelse), line)}}
+        return self.transform_ref(source, line)
+
     def properties(self, words: list[str], line: Line, lenient: bool = False) -> dict[str, Any]:
         props: dict[str, Any] = {}
         i = 0
@@ -434,7 +449,7 @@ class ScreenParser:
                     i += 1
                     if not more:
                         break
-                props["at"] = [self.transform_ref(item, line) for item in items if item]
+                props["at"] = [self.at_ref(item, line) for item in items if item]
                 continue
             if glued is not None:
                 source, i = glued, i + 1

backend/tests/test_screens.py

@@ -178,3 +178,19 @@ def test_mousearea_is_a_leaf_with_hover_actions():
     require_supported_scripts(data)
     node = data.screens["s"]["body"][0]
     assert node["w"] == "mousearea" and {"hovered", "unhovered", "xysize"} <= set(node["props"])
+
+
+def test_at_picks_a_transform_by_condition_and_atl_commas_split_statements():
+    data = parse('transform grow:\n    zoom 1.0\n    on selected:\n        zoom 1.2, 0.2\n    on deselected:\n'
+                 '        zoom 1.0, 0.2\ntransform still:\n    zoom 1.0\n'
+                 'screen s(flag):\n    frame at (grow if flag else still):\n        text "x"\n'
+                 'label start:\n    call screen s(True)\n')
+    audit_ir(data)
+    require_supported_scripts(data)
+    node = data.screens["s"]["body"][0]
+    choice = node["props"]["at"][0]["choose"]
+    assert choice["then"]["name"] == "grow" and choice["else"]["name"] == "still"
+    steps = data.atl["grow"]["steps"]
+    handler = steps[1]["block"]["steps"]
+    assert [s["op"] for s in handler] == ["set", "pause"] and handler[1]["t"] == 0.2
+    assert steps[1]["events"] == ["selected"] and steps[2]["events"] == ["deselected"]