fix(tools): search_files only defaults None/blank paths, not wrong-typed ones

The #112424 normalisation used `not isinstance(path, str) or not
path.strip()`, which also silently mapped a non-null wrong-typed path
(e.g. 5 or a list) to "." and searched the whole cwd instead of reporting
the bad argument — wider than the issue (blank/null) asked for. Restrict
the predicate to `path is None or (isinstance(path, str) and not
path.strip())` so any other type falls through to search_tool's existing
error path, exactly as on main.

Test: test_handler_preserves_nonblank_path now also covers 5 and ["src"];
those two cases fail on the previous commit (path became ".") and pass here.

tests/tools/test_search_files_engine_selection.py

@@ -305,7 +305,9 @@ def test_handler_normalizes_blank_path_to_current_directory(monkeypatch, target,
     assert captured["path"] == "."
 
 
-def test_handler_preserves_nonblank_path(monkeypatch):
+@pytest.mark.parametrize("raw_path", ["src", 5, ["src"]])
+def test_handler_preserves_nonblank_path(monkeypatch, raw_path):
+    """Only None/blank normalise to '.'; a wrong-typed path reaches search_tool's own error path."""
     captured = {}
 
     def fake_search_tool(**kwargs):
@@ -314,9 +316,9 @@ def test_handler_preserves_nonblank_path(monkeypatch):
 
     monkeypatch.setattr("tools.file_tools.search_tool", fake_search_tool)
 
-    registry.dispatch("search_files", {"pattern": "needle", "path": "src"})
+    registry.dispatch("search_files", {"pattern": "needle", "path": raw_path})
 
-    assert captured["path"] == "src"
+    assert captured["path"] == raw_path
 
 
 def test_repeated_search_key_distinguishes_order(monkeypatch):

tools/file_tools.py

@@ -1294,7 +1294,7 @@ def _handle_search_files(args, **kw):
     # The schema documents path='.'; a present-but-blank (or JSON null) value
     # is not a missing key for dict.get, so apply the default here (#112424).
     path = args.get("path", ".")
-    if not isinstance(path, str) or not path.strip():
+    if path is None or (isinstance(path, str) and not path.strip()):
         path = "."
     return search_tool(
         pattern=args.get("pattern", ""), target=target, path=path,