N-th fix od model DL

packages/tracker/meshnet_tracker/server.py

@@ -3836,12 +3836,21 @@ class _TrackerHandler(http.server.BaseHTTPRequestHandler):
             "shard_end": shard_end,
         })
         full_query = urllib.parse.urlencode({"model": model, "full": 1})
+        full_files = _snapshot_regular_files(snapshot_dir)
+        file_sizes: dict[str, int] = {}
+        for rel in set(files) | set(full_files):
+            try:
+                file_sizes[rel] = (snapshot_dir / rel).resolve().stat().st_size
+            except OSError:
+                continue
         return [{
             "type": "tracker",
             "endpoint": base_url,
             "url": f"{base_url}/v1/model-files/download?{query}",
             "full_url": f"{base_url}/v1/model-files/download?{full_query}",
             "files": files,
+            "full_files": full_files,
+            "file_sizes": file_sizes,
         }]
 
     def _handle_model_files_download(self, parsed: urllib.parse.ParseResult) -> None:
@@ -3877,6 +3886,42 @@ class _TrackerHandler(http.server.BaseHTTPRequestHandler):
         if not rel_files:
             self._send_json(404, {"error": "no local files matched the assigned shard"})
             return
+
+        # Single-file mode: ?file=<rel> streams one file with Content-Length so
+        # clients can verify completeness and retry per file instead of
+        # restarting one giant tar stream after a network hiccup.
+        single = params.get("file", [""])[0]
+        if single:
+            if single not in set(rel_files):
+                self._send_json(404, {"error": f"file not in requested shard: {single!r}"})
+                return
+            file_path = snapshot_dir / single
+            try:
+                # resolve() dereferences HF snapshot symlinks into blobs/.
+                size = file_path.resolve().stat().st_size
+            except OSError:
+                self._send_json(404, {"error": f"file unreadable: {single!r}"})
+                return
+            self.send_response(200)
+            self.send_header("Content-Type", "application/octet-stream")
+            self.send_header("Content-Length", str(size))
+            self.send_header("X-Meshnet-Model-Source", "tracker")
+            self.end_headers()
+            try:
+                with file_path.open("rb") as f:
+                    while True:
+                        chunk = f.read(1024 * 1024)
+                        if not chunk:
+                            break
+                        self.wfile.write(chunk)
+            except (BrokenPipeError, ConnectionResetError):
+                print(
+                    f"model-file download aborted by client "
+                    f"({self.client_address[0]}, model={resolved_name}, file={single})",
+                    flush=True,
+                )
+            return
+
         self.send_response(200)
         self.send_header("Content-Type", "application/x-tar")
         self.send_header("X-Meshnet-Model-Source", "tracker")