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diff --git a/packages/meshbay-node/tests/test_upload_sealed.py b/packages/meshbay-node/tests/test_upload_sealed.py
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+"""
+The write path, sealed under the group key (MNP 2.0).
+
+Downloads have been encrypted under a GEK-derived key since the beginning:
+`file_chunk` and `stream_data` both go through `chunk_ciphertext`. Uploads did
+not. `file_upload` carried the filename and the raw bytes in plain msgpack and
+`file_upload_ack` carried the name the node stored them under, so the same file
+was ciphertext leaving a node and plaintext arriving at one — an asymmetry with
+no threat model behind it.
+
+What sealing buys is what `groupbox.py` says and no more: nothing against a
+network observer (DTLS covers that), nothing against the hub (never on this
+channel), nothing against a member (they hold the GEK). It buys defence in
+depth against our own next handshake bug, of a class already shipped twice —
+C1, the unauthenticated node HTTP API, and C6, the transport that took a bare
+JWT. Both were "a peer that had not finished the handshake was served data".
+Sealed, the equivalent bug on this path leaks ciphertext instead of the
+operator's filenames.
+"""
+
+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 MNP, file_upload_wire
+from meshbay_node.indexer.group_index import GroupIndex
+from meshbay_node.transport.webrtc_server import WebRTCPeerSession
+
+from conftest import one_root, opened_ack, sealed_upload
+
+GROUP = "g" * 32
+
+
+def _session(tmp_path: Path, *, gek: bytes | None = None) -> WebRTCPeerSession:
+    shared_root = tmp_path / "shared"
+    shared_root.mkdir(exist_ok=True)
+    index = GroupIndex(group_id=GROUP, sk_node=Ed25519PrivateKey.generate())
+    session = WebRTCPeerSession.__new__(WebRTCPeerSession)
+    session._ctx = {"roots": one_root(shared_root), "index": index,
+                    "sk_node": index.sk_node, "gek": gek or generate_gek()}
+    session._group_id = GROUP
+    session._user_id = "user-1"
+    session._pk_user = ""
+    session._uploads = {}
+    session.sent = []
+    session._send = session.sent.append
+    session._audit = lambda *a, **k: None
+    return session
+
+
+def _root(session):
+    return session._ctx["roots"].roots[0]
+
+
+def _errors(session):
+    return [m for m in session.sent if m.get("type") == "error"]
+
+
+def _wrote_anything(tmp_path) -> bool:
+    return any(p.is_file() for p in tmp_path.rglob("*"))
+
+
+# ── The message itself ───────────────────────────────────────────────────────
+
+def test_the_wire_message_carries_no_filename_and_no_plaintext(tmp_path):
+    """
+    The point of the exercise. `upload_id` and `chunk_index` are outside the
+    seal because the node routes and orders on them before it can decrypt;
+    everything that names or is the operator's content is inside it.
+    """
+    session = _session(tmp_path)
+    msg = sealed_upload(session, filename="holiday.jpg", data=b"JPEGDATA",
+                        dir=f"{_root(session).name}")
+
+    assert set(msg) == {"type", "v", "upload_id", "chunk_index",
+                        "total_chunks", "nonce", "ct"}
+    blob = repr(msg).encode() + msg["ct"]
+    assert b"holiday.jpg" not in blob, "the filename is on the wire in clear"
+    assert b"JPEGDATA" not in blob, "the file content is on the wire in clear"
+
+
+def test_the_ack_carries_no_stored_name(tmp_path):
+    """
+    `stored_as` is the name the node settled on — it finds a free one rather
+    than replacing anything — and naming it in clear would hand back exactly
+    what the request took the trouble to hide.
+    """
+    session = _session(tmp_path)
+    session._do_file_upload(sealed_upload(
+        session, filename="holiday.jpg", data=b"x", dir=_root(session).name))
+
+    ack = [m for m in session.sent if m.get("type") == MNP.FILE_UPLOAD_ACK][-1]
+    assert set(ack) == {"type", "v", "upload_id", "chunk_index", "nonce", "ct"}
+    assert b"holiday.jpg" not in repr(ack).encode() + ack["ct"]
+    assert opened_ack(session, ack) == {
+        "filename": "holiday.jpg", "stored_as": "holiday.jpg",
+        "dir": _root(session).name}
+
+
+def test_the_ack_names_the_upload_so_one_refusal_fails_one_upload(tmp_path):
+    """
+    `filename` used to be the correlation key on both sides. It cannot be one
+    any more, and `upload_id` replaces it — a client-chosen label, opaque to
+    the node, never an authorization input. Without it a client running several
+    uploads could only match replies by arrival order, which is how a refusal
+    for one file used to fail every upload in flight.
+    """
+    session = _session(tmp_path)
+    session._do_file_upload(sealed_upload(
+        session, filename="a.txt", data=b"x", dir=_root(session).name,
+        upload_id="upload-A"))
+    session._do_file_upload(sealed_upload(
+        session, filename="../evil", data=b"x", dir=_root(session).name,
+        upload_id="upload-B"))
+
+    ack = [m for m in session.sent if m.get("type") == MNP.FILE_UPLOAD_ACK][-1]
+    assert ack["upload_id"] == "upload-A"
+    assert _errors(session)[0]["upload_id"] == "upload-B"
+
+
+# ── What is refused ──────────────────────────────────────────────────────────
+
+def test_a_plaintext_upload_is_refused(tmp_path):
+    """
+    The MNP 1.x shape, which is what an un-updated client sends. Refused with a
+    code and a message saying which side is old — never accepted "just this
+    once", because a path that still takes plaintext is not a sealed path.
+    """
+    session = _session(tmp_path)
+    session._do_file_upload({
+        "filename": "note.txt", "dir": _root(session).name,
+        "chunk_index": 0, "total_chunks": 1, "data": b"x",
+    })
+
+    assert _errors(session)[0]["code"] == "upload_not_sealed"
+    assert not _wrote_anything(tmp_path)
+
+
+def test_a_tampered_chunk_is_refused(tmp_path):
+    """
+    AES-GCM's tag, asserted where it matters: a flipped bit in the ciphertext
+    must stop the upload, not produce a corrupt file with a plausible name.
+    """
+    session = _session(tmp_path)
+    msg = sealed_upload(session, filename="note.txt", data=b"x" * 64,
+                        dir=_root(session).name)
+    msg["ct"] = bytes([msg["ct"][0] ^ 0x01]) + msg["ct"][1:]
+    session._do_file_upload(msg)
+
+    assert _errors(session)[0]["code"] == "upload_not_sealed"
+    assert not _wrote_anything(tmp_path)
+
+
+def test_an_upload_sealed_for_another_group_is_refused(tmp_path):
+    """
+    The group is the AAD, so a node hosting two groups cannot have a chunk
+    moved between them — and a member of one cannot write into the other by
+    reaching a session that is on it (finding H1's shape, on the write path).
+    """
+    session = _session(tmp_path)
+    msg = file_upload_wire(
+        session._ctx["gek"], "some-other-group",
+        upload_id="u1", chunk_index=0, total_chunks=1,
+        filename="note.txt", data=b"x", dir=_root(session).name)
+    session._do_file_upload(msg)
+
+    assert _errors(session)[0]["code"] == "upload_not_sealed"
+    assert not _wrote_anything(tmp_path)
+
+
+def test_an_upload_under_another_key_is_refused(tmp_path):
+    """A peer past the handshake with the wrong GEK still writes nothing."""
+    session = _session(tmp_path)
+    msg = file_upload_wire(
+        generate_gek(), GROUP,
+        upload_id="u1", chunk_index=0, total_chunks=1,
+        filename="note.txt", data=b"x", dir=_root(session).name)
+    session._do_file_upload(msg)
+
+    assert _errors(session)[0]["code"] == "upload_not_sealed"
+    assert not _wrote_anything(tmp_path)
+
+
+def test_an_ack_replayed_as_a_request_does_not_open(tmp_path):
+    """
+    The message type is in the AAD, so the two halves of an upload cannot be
+    confused for each other. Cheap, and it closes a class that is tedious to
+    reason about after the fact.
+    """
+    from cryptography.exceptions import InvalidTag
+    from meshbay_common.protocol import file_upload_ack_wire, file_upload_payload
+
+    session = _session(tmp_path)
+    ack = file_upload_ack_wire(
+        session._ctx["gek"], GROUP, upload_id="u1", chunk_index=0,
+        filename="note.txt", stored_as="note.txt", dir="shared")
+    with pytest.raises(InvalidTag):
+        file_upload_payload(session._ctx["gek"], GROUP, ack)
+
+
+def test_a_group_with_no_key_refuses_rather_than_falling_back(tmp_path):
+    """
+    A node whose group has no GEK yet cannot open anything. It must say so, not
+    read the message as though it were the old plaintext shape.
+    """
+    session = _session(tmp_path)
+    msg = sealed_upload(session, filename="note.txt", data=b"x",
+                        dir=_root(session).name)
+    session._ctx["gek"] = b""
+    session._do_file_upload(msg)
+
+    assert _errors(session)[0]["code"] == "no_group_key"
+    assert not _wrote_anything(tmp_path)
+
+
+# ── What must still work ─────────────────────────────────────────────────────
+
+def test_a_multi_chunk_upload_reassembles(tmp_path):
+    """
+    Every chunk is sealed under its own nonce, and the node appends in order.
+    Nothing about the seal may change what lands on disk.
+    """
+    session = _session(tmp_path)
+    body = bytes(range(256)) * 40
+    parts = [body[i:i + 1024] for i in range(0, len(body), 1024)]
+    for i, part in enumerate(parts):
+        session._do_file_upload(sealed_upload(
+            session, filename="blob.bin", data=part,
+            chunk_index=i, total_chunks=len(parts), dir=_root(session).name))
+
+    assert (_root(session).path / "blob.bin").read_bytes() == body
+    assert not list(_root(session).path.glob("*.part")), "a temp file was left"
+    acks = [m for m in session.sent if m.get("type") == MNP.FILE_UPLOAD_ACK]
+    assert [m["chunk_index"] for m in acks] == list(range(len(parts)))
+
+
+def test_two_identical_chunks_do_not_reuse_a_nonce(tmp_path):
+    """
+    A file of repeated bytes is ordinary, so the nonce must come from the RNG
+    and never from the payload. Cheap to assert and expensive to discover.
+    """
+    session = _session(tmp_path)
+    a = sealed_upload(session, filename="f", data=b"same", chunk_index=0)
+    b = sealed_upload(session, filename="f", data=b"same", chunk_index=0)
+    assert a["nonce"] != b["nonce"]
+    assert a["ct"] != b["ct"]
+
+
+def test_a_sealed_payload_is_authenticated_not_validated(tmp_path):
+    """
+    Opening a payload proves a member wrote it, not that they wrote something
+    sensible. A member can seal anything, so the fields still need their types
+    checked — `SAFE_UPLOAD_NAME.match(123)` raises where a refusal was meant,
+    and the dispatcher's catch-all would turn that into "Request failed".
+    """
+    from meshbay_common.groupbox import PURPOSE_UPLOAD, seal
+
+    session = _session(tmp_path)
+    for payload in ({"filename": 123, "data": b"x"},
+                    {"filename": "note.txt", "data": "not bytes"},
+                    {"filename": "note.txt"}):
+        session.sent.clear()
+        session._do_file_upload({
+            "type": MNP.FILE_UPLOAD, "v": "2.0", "upload_id": "u1",
+            "chunk_index": 0, "total_chunks": 1,
+            **seal(session._ctx["gek"], PURPOSE_UPLOAD, MNP.FILE_UPLOAD,
+                   GROUP, payload),
+        })
+        errs = _errors(session)
+        assert errs, f"{payload!r} was accepted"
+        assert errs[0]["code"] in ("upload_incomplete", "bad_chunk_encoding")
+    assert not _wrote_anything(tmp_path)
+
+
+def test_a_peer_controlled_chunk_index_cannot_crash_the_handler(tmp_path):
+    """`chunk_index` is outside the seal by necessity, so it is unchecked input."""
+    session = _session(tmp_path)
+    msg = sealed_upload(session, filename="note.txt", data=b"x",
+                        dir=_root(session).name)
+    msg["chunk_index"] = "zero"
+    session._do_file_upload(msg)
+
+    assert _errors(session)[0]["code"] == "bad_chunk_index"
+    assert not _wrote_anything(tmp_path)