fix: downloads are marked and keep their extension; Explorer files are refused

The desktop app writes the Mark-of-the-Web on each file it saves on Windows, as
a browser does. Bidirectional controls are reserved characters in a saved name
(portable-name.js and paths.sanitize_for_download, and again in the main
process), so a name cannot display one extension and carry another. The node
refuses uploads of files Windows Explorer acts on by itself: desktop.ini,
.lnk, .url, .scf, .library-ms, .searchConnector-ms (F-19).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/packages/meshbay-node/tests/test_partial_uploads.py b/packages/meshbay-node/tests/test_partial_uploads.py
index 138ee3b..556b26a 100644
--- a/packages/meshbay-node/tests/test_partial_uploads.py
+++ b/packages/meshbay-node/tests/test_partial_uploads.py
@@ -22,6 +22,7 @@ import time
 import types
 from pathlib import Path
 
+import pytest
 from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey
 from meshbay_common.crypto import generate_gek
 from meshbay_common.protocol import (
@@ -552,3 +553,23 @@ def test_without_hard_links_a_file_is_still_not_replaced(tmp_path, monkeypatch):
     assert (tmp_path / "a.txt").read_bytes() == b"there first"
     assert (tmp_path / "a (2).txt").read_bytes() == b"uploaded"
     assert not part.exists()
+
+
+# ── files Explorer acts on by itself ─────────────────────────────────────────
+
+
+@pytest.mark.parametrize("name", ["desktop.ini", "Desktop.INI", "photos.lnk", "site.url",
+                                  "x.scf", "Docs.library-ms", "s.searchConnector-ms"])
+async def test_a_file_explorer_acts_on_is_refused(tmp_path, name):
+    ctx = _group_ctx(tmp_path)
+    peer = _peer(ctx)
+    await peer._do_file_upload(sealed_upload(peer, filename=name, data=b"[x]"))
+    assert [m.get("code") for m in _errors(peer)] == ["file_type_refused"]
+    assert not any(ctx["roots"].roots[0].path.iterdir())
+
+
+async def test_an_ordinary_file_with_a_near_name_is_accepted(tmp_path):
+    ctx = _group_ctx(tmp_path)
+    peer = _peer(ctx)
+    await peer._do_file_upload(sealed_upload(peer, filename="url-notes.txt", data=b"x"))
+    assert _errors(peer) == []