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, 11 insertions, 1 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc/upload_handlers.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc/upload_handlers.py
index f1ed139..02a50af 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc/upload_handlers.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/upload_handlers.py
@@ -8,7 +8,14 @@ from pathlib import Path
 from meshbay_common.protocol import UPLOAD_PROBE_INDEX, file_upload_ack_wire, file_upload_payload
 
 from meshbay_node import uploads as uploads_mod
-from meshbay_node.roots import SAFE_UPLOAD_NAME, RootSet, _free_name, off_disk, publish_upload
+from meshbay_node.roots import (
+    SAFE_UPLOAD_NAME,
+    RootSet,
+    _free_name,
+    off_disk,
+    publish_upload,
+    shell_active,
+)
 from meshbay_node.transport.webrtc.disk import _append_chunk
 from meshbay_node.transport.webrtc.limits import LEASE_NONE, LEASE_QUEUED
 
@@ -212,6 +219,9 @@ class UploadMixin:
         if not SAFE_UPLOAD_NAME.match(filename):
             _refuse("Invalid filename", "invalid_filename")
             return
+        if shell_active(filename):
+            _refuse("This type of file is not accepted", "file_type_refused")
+            return
 
         roots: RootSet | None = ctx.get("roots")
         if not roots: