feat(node): an upload lands in the folder it was sent to

There is no `uploads/` subdirectory any more, and the client names the folder
rather than the root.

It was the last of v5's quarantine — the per-user layer went on 2026-08-14 for
the same reason — and it goes on the same grounds: a folder appearing beside
the operator's library because somebody sent a file is the node deciding how
their disk is arranged. Somebody dropping a file into the folder they are
looking at expects it to be in that folder.

**What made the quarantine worth having was never the subdirectory.** It is the
filename allowlist, the size cap, the chunk ordering and the no-overwrite rule,
and all four are untouched: an existing file is never replaced, the second
sender of IMG_1234.jpg gets a free name, and the check still sits at the write.

Letting the client choose the destination is safe for one reason and only one:
it is resolved through `RootSet.resolve()`, which refuses `..`, absolute
segments and anything whose resolved form escapes its root, symlinks included.
A member answers "which of this group's folders", never "which path on the
operator's disk" — and the test that used to assert the node chose now asserts
that, with six shapes of escape.

`direct` goes with it. Its only job was to say "no subdirectory for this root",
which is now every root, and a config flag that does nothing is worse than none.

Chat's attachment folder finally does something: the directory the operator
picks in the Chat settings pane is where attachments are written, falling back
to the first writable root while they have not chosen one, or if the one they
chose has since been made read-only or ejected — a stale choice should not
become a refusal at send time.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011pvMdvLBG92jyhvD5pD6us

1 files changed, 5 insertions, 3 deletions

diff --git a/packages/meshbay-node/tests/test_root_writable_policy.py b/packages/meshbay-node/tests/test_root_writable_policy.py
index da95032..d7f2666 100644
--- a/packages/meshbay-node/tests/test_root_writable_policy.py
+++ b/packages/meshbay-node/tests/test_root_writable_policy.py
@@ -62,14 +62,16 @@ def _session(tmp_path: Path, user_id: str, *,
 
 def _upload(session, filename="clip.mp4", body=b"bytes"):
     session._do_file_upload({
-        "filename": filename, "root": "shared",
+        "filename": filename, "dir": "shared",
         "chunk_index": 0, "total_chunks": 1,
         "data": base64.b64encode(body).decode(),
     })
 
 
 def _uploads_dir(session) -> Path:
-    return session._ctx["roots"].roots[0].path / "uploads"
+    # The root itself: the `uploads/` subdirectory the node used to create is
+    # gone (see test_security_regressions._uploads_dir for why).
+    return session._ctx["roots"].roots[0].path
 
 
 # ── The door, not the button ─────────────────────────────────────────────────
@@ -80,7 +82,7 @@ async def test_a_member_cannot_upload_to_a_read_only_root(tmp_path):
 
     refusal = [m for m in session.sent if m.get("type") == "error"]
     assert refusal and refusal[0].get("code") == "root_read_only"
-    assert not _uploads_dir(session).exists()
+    assert not (_uploads_dir(session) / "clip.mp4").exists()
 
 
 async def test_members_upload_normally_to_a_writable_root(tmp_path):