diff --git a/src/docgen/scene_asset_validate.py b/src/docgen/scene_asset_validate.py
index e228fe5..5de31a1 100644
--- a/src/docgen/scene_asset_validate.py
+++ b/src/docgen/scene_asset_validate.py
@@ -250,8 +250,83 @@ def extract_class_source(scenes_text: str, class_name: str) -> str | None:
     return None
 
 
+_CANONICAL_HELPERS = ("_box", "_arrow", "_TimedScene", "_load_timing", "_load_timing_words")
+_TIMED_SCENE_METHODS = frozenset({"timed_play", "wait_until_word"})
+
+
+def _unique(names: list[str]) -> list[str]:
+    return list(dict.fromkeys(names))
+
+
+def _note_renamed_timed_scene(node: ast.AST, renamed: list[str]) -> None:
+    if not isinstance(node, ast.ClassDef) or node.name == "_TimedScene":
+        return
+    methods = {
+        child.name
+        for child in node.body
+        if isinstance(child, (ast.FunctionDef, ast.AsyncFunctionDef))
+    }
+    if _TIMED_SCENE_METHODS.intersection(methods):
+        renamed.append(node.name)
+
+
+def _note_helper_node(node: ast.AST, inlined: list[str], referenced: list[str], renamed: list[str]) -> None:
+    if isinstance(node, (ast.FunctionDef, ast.AsyncFunctionDef, ast.ClassDef)):
+        if node.name in _CANONICAL_HELPERS:
+            inlined.append(node.name)
+        _note_renamed_timed_scene(node, renamed)
+    elif isinstance(node, ast.Name) and node.id in _CANONICAL_HELPERS:
+        referenced.append(node.id)
+
+
+def _helper_issue_parts(inlined: list[str], referenced: list[str], renamed: list[str]) -> list[str]:
+    parts: list[str] = []
+    if inlined:
+        parts.append("inlined " + ", ".join(_unique(inlined)))
+    if renamed:
+        parts.append("renamed _TimedScene-style " + ", ".join(_unique(renamed)))
+    missing = [name for name in _unique(referenced) if name not in inlined]
+    if missing:
+        parts.append("referenced but not top-level " + ", ".join(missing))
+    return parts
+
+
+def _inlined_or_renamed_helper_issue(tree: ast.AST) -> str | None:
+    """Fail closed when canonical helpers are not top-level defs.
+
+    Nested ``_box`` / ``_TimedScene`` bodies, calls or bases that name them, and
+    classes that carry ``timed_play`` / ``wait_until_word`` under another name
+    used to skip :func:`helper_needs_refresh` entirely.
+    """
+    inlined: list[str] = []
+    referenced: list[str] = []
+    renamed: list[str] = []
+    for node in ast.walk(tree):
+        _note_helper_node(node, inlined, referenced, renamed)
+    if not inlined and not referenced and not renamed:
+        return None
+    detail = "; ".join(_helper_issue_parts(inlined, referenced, renamed))
+    return (
+        "helpers: canonical _box / _arrow / _TimedScene / _load_timing / "
+        "_load_timing_words are missing or inlined "
+        f"({detail}) — stale-helper check cannot pass silently; "
+        "run `docgen scene-compile` to restore top-level helper bodies"
+    )
+
+
+def _missing_top_level_helper_issues(tree: ast.AST) -> list[str]:
+    issue = _inlined_or_renamed_helper_issue(tree)
+    if issue:
+        return [issue]
+    return []
+
+
 def helper_api_violations(scenes_text: str) -> list[str]:
-    """Stale ``_box`` / ``_arrow`` / ``_TimedScene`` that will mis-render new specs."""
+    """Stale ``_box`` / ``_arrow`` / ``_TimedScene`` that will mis-render new specs.
+
+    Helpers must be top-level. Inlined or renamed ``_TimedScene``-style helpers
+    fail closed with an explicit missing/inlined message.
+    """
     from docgen.manim_scene_support import helper_needs_refresh
 
     try:
@@ -262,8 +337,8 @@ def helper_api_violations(scenes_text: str) -> list[str]:
     for node in tree.body:
         if isinstance(node, (ast.FunctionDef, ast.ClassDef)):
             defined.add(node.name)
-    if not defined.intersection({"_box", "_arrow", "_TimedScene", "_load_timing", "_load_timing_words"}):
-        return []
+    if not defined.intersection(set(_CANONICAL_HELPERS)):
+        return _missing_top_level_helper_issues(tree)
     issues: list[str] = []
     if "MANIM_FONT" not in scenes_text:
         issues.append(
diff --git a/tests/test_scene_asset_validate.py b/tests/test_scene_asset_validate.py
index 9f2ef6d..9148642 100644
--- a/tests/test_scene_asset_validate.py
+++ b/tests/test_scene_asset_validate.py
@@ -263,6 +263,40 @@ def test_helper_api_clean_for_current_bootstrap() -> None:
     assert helper_api_violations(BOOTSTRAP_HEADER) == []
 
 
+def test_helper_api_flags_inlined_or_renamed_helpers() -> None:
+    inlined = """
+class OverviewScene:
+    class _TimedScene:
+        def timed_play(self, *a, run_time=1.0):
+            pass
+        def wait_until_word(self, words, index):
+            return
+    def construct(self):
+        _box("Alpha", "#fff")
+"""
+    inlined_issues = helper_api_violations(inlined)
+    assert any(
+        "missing or inlined" in issue and "inlined _TimedScene" in issue
+        for issue in inlined_issues
+    )
+    assert any("_box" in issue for issue in inlined_issues)
+
+    renamed = """
+class SceneClock:
+    def timed_play(self, *a, run_time=1.0):
+        pass
+    def wait_until_word(self, words, index):
+        return
+"""
+    renamed_issues = helper_api_violations(renamed)
+    assert any(
+        "missing or inlined" in issue and "renamed _TimedScene-style SceneClock" in issue
+        for issue in renamed_issues
+    )
+
+    assert helper_api_violations("def render():\n    return 1\n") == []
+
+
 def test_compiled_sync_passes_when_scenes_match_compile() -> None:
     spec = _spec([_box("Alpha", wait_word=0), _box("Beta", wait_word=1)])
     words = _wide_words()