diff --git a/tests/test_websocket_broadcast_regression.py b/tests/test_websocket_broadcast_regression.py
new file mode 100644
index 00000000..2425e6cc
--- /dev/null
+++ b/tests/test_websocket_broadcast_regression.py
@@ -0,0 +1,70 @@
+"""Regression test for the WebSocketServer.broadcast() runtime TypeError bug.
+
+Phase 5 of any_type_componentization_20260621 changed
+WebSocketServer.broadcast(channel, payload) -> broadcast(message: WebSocketMessage)
+but did not update internal callers in src/app_controller.py + src/events.py.
+This produced worker[queue_fallback] TypeError spam on the GUI thread.
+
+This test catches the regression and is reused by code_path_audit_20260607
+as a structural assertion.
+
+CONVENTION: 1-space indentation. NO COMMENTS.
+"""
+from __future__ import annotations
+
+import inspect
+from pathlib import Path
+from typing import Any
+
+from src.api_hooks import WebSocketMessage, WebSocketServer
+
+
+class _MockApp:
+ test_hooks_enabled: bool = True
+
+
+def _make_server() -> WebSocketServer:
+ return WebSocketServer(_MockApp(), port=9001)
+
+
+def test_websocket_server_broadcast_signature() -> None:
+ """WebSocketServer.broadcast must accept a single WebSocketMessage argument (self + message)."""
+ sig = inspect.signature(WebSocketServer.broadcast)
+ params = list(sig.parameters.keys())
+ assert len(params) == 2, f"expected 2 params (self + message), got {len(params)}: {params}"
+
+
+def test_websocket_server_broadcast_rejects_legacy_2arg_call() -> None:
+ """Calling broadcast with 2 positional args (legacy signature) must raise TypeError."""
+ server = _make_server()
+ raised = False
+ try:
+  server.broadcast("channel", {"key": "value"})
+ except TypeError:
+  raised = True
+ assert raised, "broadcast should reject legacy 2-arg call"
+
+
+def test_websocket_server_broadcast_accepts_websocket_message_instance() -> None:
+ """The new signature accepts a WebSocketMessage instance (no-op when not started)."""
+ server = _make_server()
+ msg = WebSocketMessage(channel="test", payload={"key": "value"})
+ server.broadcast(msg)
+
+
+def test_internal_callers_use_websocket_message_signature() -> None:
+ """Grep all internal callers of broadcast() in src/ and assert they use the new signature."""
+ src_root = Path(__file__).resolve().parents[1] / "src"
+ legacy_sites: list[str] = []
+ for py_file in src_root.rglob("*.py"):
+  text = py_file.read_text(encoding="utf-8")
+  for lineno, line in enumerate(text.splitlines(), start=1):
+   if ".broadcast(" not in line:
+    continue
+   if "WebSocketMessage(" in line:
+    continue
+   if 'broadcast("' not in line and "broadcast('" not in line:
+    continue
+   rel = py_file.relative_to(src_root.parent)
+   legacy_sites.append(f"{rel}:{lineno}: {line.strip()}")
+ assert not legacy_sites, "legacy broadcast() callers found:\n" + "\n".join(legacy_sites)
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