diff --git a/features/steps/tui_first_run_steps.py b/features/steps/tui_first_run_steps.py
index b6e9ca9db..fad2ae17e 100644
--- a/features/steps/tui_first_run_steps.py
+++ b/features/steps/tui_first_run_steps.py
@@ -488,3 +488,47 @@ def step_persona_bar_reflects_actor(context: object) -> None:
     assert "anthropic/claude-sonnet-4-20250514" in bar._text, (
         f"Expected actor in persona bar, got: {bar._text}"
     )
+
+
+# ---------------------------------------------------------------------------
+# TDD regression: issue #11039 - no _render() shadowing Textual Widget._render
+# ---------------------------------------------------------------------------
+
+
+@then("the overlay should not override Textual Widget._render")
+def step_overlay_no_render_override(context: object) -> None:
+    """Verify that ActorSelectionOverlay does NOT define its own ``_render``.
+
+    The Shadowing Bug (issue #11039): ActorSelectionOverlay once defined
+    ``def _render(self) -> None`` which returned ``None``, shadowing
+    ``textual.widgets.Static._render()`` (which returns a
+    :class:`textual.strip.Strip`). This caused the Textual layout engine to
+    crash with ``AttributeError: 'NoneType' object has no attribute
+    'get_height'``.
+
+    The fix renamed the method to ``_refresh_display`` so that the inherited
+    base-class ``_render`` is untouched and returns a proper renderable.
+    """
+    from cleveragents.tui.widgets.actor_selection_overlay import (
+        ActorSelectionOverlay,
+    )
+
+    cls = ActorSelectionOverlay
+    # The overlay should NOT define its own _render in its __dict__.
+    # If it did, _render found on the class would resolve to this method
+    # rather than the Textual base-class implementation.
+    has_own_render = "_render" in cls.__dict__
+    assert not has_own_render, (
+        "ActorSelectionOverlay defines its own _render() which shadows "
+        "Textual Widget._render. This is the bug from issue #11039."
+    )
+
+
+@then("the overlay _refresh_display method should be callable")
+def step_overlay_refresh_display_callable(context: object) -> None:
+    """Verify ``_refresh_display`` exists and is callable after show()."""
+    assert hasattr(
+        context._overlay, "_refresh_display"
+    ), "Overlay must have _refresh_display method"
+    refresh = context._overlay._refresh_display
+    assert callable(refresh), "_refresh_display must be callable"
diff --git a/features/tui_first_run.feature b/features/tui_first_run.feature
index 3d82993da..c8646de05 100644
--- a/features/tui_first_run.feature
+++ b/features/tui_first_run.feature
@@ -194,3 +194,21 @@ Feature: TUI first-run experience with actor selection overlay
     And I call _complete_first_run with actor "anthropic/claude-sonnet-4-20250514"
     Then the registry should contain a persona named "default"
     And the persona bar should reflect the new actor
+
+  # -----------------------------------------------------------------------
+  # TDD regression: issue #11039 - no _render() shadowing Textual Widget._render
+  # -----------------------------------------------------------------------
+  # The overlay formerly defined its own _render() returning None, which
+  # shadowed textual.widgets.Static._render and caused layout-engine crashes.
+  # This scenario ensures the rename to _refresh_display eliminated that bug.
+
+  @tdd_issue @tdd_issue_11039
+  Scenario: ActorSelectionOverlay does not define its own _render method
+    Given a new ActorSelectionOverlay
+    Then the overlay should not override Textual Widget._render
+
+  @tdd_issue @tdd_issue_11039
+  Scenario: ActorSelectionOverlay has refresh_display callable instead of render
+    Given a new ActorSelectionOverlay
+    When I call show on the overlay
+    Then the overlay _refresh_display method should be callable