test(tools): pin open_preview missing-path emit (#95853)

Independent review: document OSError fail-open on is_dir, and lock
that only existing directories are rejected.

tests/tools/test_open_preview_tool.py

@@ -80,3 +80,14 @@ def test_file_uri_directory_is_an_error(tmp_path):
     assert "error" in result
     assert "director" in result["error"].lower()
     assert emitted == []
+
+
+def test_missing_path_still_emits(tmp_path):
+    """Reject only existing directories — a missing path is the renderer's call."""
+    emitted = _capture_emits()
+    missing = tmp_path / "no-such-folder"
+
+    result = json.loads(op.open_preview_tool(str(missing)))
+
+    assert result["success"] is True
+    assert emitted == [("preview.open", {"url": str(missing), "label": ""})]

tools/open_preview_tool.py

@@ -61,6 +61,9 @@ def _is_existing_directory(target: str) -> bool:
     try:
         return path.is_dir()
     except OSError:
+        # Stat failed (permissions, broken reparse, etc.). Do not treat that
+        # as "this is a directory" — reject only when we positively observe
+        # an existing directory. The renderer still sees the original target.
         return False