Add guard test for shared manager serialization path

Co-authored-by: Shri Sukhani <shrisukhani@users.noreply.github.com>

Author: cursoragent

tests/test_manager_model_dump_usage.py

@@ -0,0 +1,31 @@
+import ast
+from pathlib import Path
+
+
+MANAGERS_DIR = Path(__file__).resolve().parents[1] / "hyperbrowser" / "client" / "managers"
+
+
+def _manager_python_files() -> list[Path]:
+    return sorted(
+        path
+        for path in MANAGERS_DIR.rglob("*.py")
+        if path.name not in {"serialization_utils.py", "__init__.py"}
+    )
+
+
+def test_manager_modules_use_shared_serialization_helper_only():
+    offending_calls: list[str] = []
+
+    for path in _manager_python_files():
+        source = path.read_text(encoding="utf-8")
+        module = ast.parse(source, filename=str(path))
+        for node in ast.walk(module):
+            if not isinstance(node, ast.Call):
+                continue
+            if not isinstance(node.func, ast.Attribute):
+                continue
+            if node.func.attr != "model_dump":
+                continue
+            offending_calls.append(f"{path.relative_to(MANAGERS_DIR)}:{node.lineno}")
+
+    assert offending_calls == []