feat(node): refuse an upload on a full disk with a stated reason

Nothing on the upload path knew about ENOSPC: a write that found no room
raised out of the handler, the catch-all answered "Request failed", and the
.part stayed behind holding the space that had run out. The node now refuses
with `disk_full` at chunk 0 when the announced size would leave less than
1 GiB free, and at any write that fails with ENOSPC/EDQUOT, dropping the
partial. The client carries the code on the error and the transfers panel
says "The node's disk is full" in every catalogue.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc/disk.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc/disk.py
index 2e484de..e298942 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc/disk.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/disk.py
@@ -1,5 +1,6 @@
 """Blocking disk work the session hands to `off_disk`."""
 
+import shutil
 from pathlib import Path
 
 from meshbay_common.protocol import file_chunk_wire
@@ -76,6 +77,12 @@ def _read_and_encrypt(
     return file_chunk_wire(gek, plaintext, chunk_index, file_hash, file_id)
 
 
+def _free_bytes(directory: Path) -> int:
+    """Space left on the filesystem holding `directory`. Blocking; called
+    through `off_disk`, since a `statvfs` wakes a sleeping disk like any stat."""
+    return shutil.disk_usage(directory).free
+
+
 def _append_chunk(tmp_path: Path, chunk_bytes: bytes, first: bool) -> None:
     """Add one chunk to a partial upload. Blocking; called through `off_disk`."""
     with open(tmp_path, "wb" if first else "ab") as f: