fix: resolve per-torrent qb save paths

src/archive_clients/resources.py

@@ -23,6 +23,9 @@ class NormalizedResource:
     files: tuple[resource_pb2.TorrentFile, ...]
     metainfo: Metainfo
     metainfo_bytes: bytes = b""
+    # qBittorrent's API-visible save path is intentionally local-only.  It
+    # must never become part of inventory or placement protocol messages.
+    save_path: PurePosixPath | None = None
 
 
 def build_content_tree(
@@ -137,6 +140,7 @@ def normalize_resource(
         character not in "0123456789abcdef" for character in qb_torrent_id
     ):
         raise ResourceError("torrent hash is invalid")
+    save_path = _save_path(torrent.get("save_path"))
     summary = resource_pb2.ResourceSummary(
         qb_torrent_id=qb_torrent_id,
         display_name=_string(torrent.get("name"), "torrent name"),
@@ -172,7 +176,9 @@ def normalize_resource(
         revision_data, sort_keys=True, separators=(",", ":"),
     ).encode("utf-8")).hexdigest()
     summary.observed_at.FromDatetime(observed_at)
-    return NormalizedResource(summary, tuple(files), metainfo, metainfo_bytes)
+    return NormalizedResource(
+        summary, tuple(files), metainfo, metainfo_bytes, save_path
+    )
 
 
 def _set_selection(target: Any, indices: list[int]) -> None:
@@ -217,6 +223,20 @@ def _path(value: Any) -> str:
     return candidate.as_posix()
 
 
+def _save_path(value: Any) -> PurePosixPath:
+    """Validate qBittorrent's API-visible per-torrent content root."""
+
+    path = _string(value, "torrent save path")
+    candidate = PurePosixPath(path)
+    if (
+        not candidate.is_absolute()
+        or ".." in candidate.parts
+        or "." in candidate.parts
+    ):
+        raise ResourceError("qBittorrent torrent save path is unsafe")
+    return candidate
+
+
 def _integer(value: Any, name: str) -> int:
     if isinstance(value, bool) or not isinstance(value, int) or value < 0:
         raise ResourceError(f"{name} is invalid")