2 files changed, 33 insertions, 0 deletions
diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc/core.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc/core.py
index ae3f0e1..a44f097 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc/core.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/core.py
@@ -14,6 +14,7 @@ from meshbay_common.protocol import MNP
 
 from meshbay_node import ops
 from meshbay_node import transfers as transfers_mod
+from meshbay_node.transport.webrtc import sctp_fix  # noqa: F401  (patches aiortc on import)
 from meshbay_node.transport.webrtc.channel import (
     _REPLY_TO,
     _DataChannelBuffer,
diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc/sctp_fix.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc/sctp_fix.py
new file mode 100644
index 0000000..0d45a7d
--- /dev/null
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/sctp_fix.py
@@ -0,0 +1,32 @@
+"""A fix to aiortc's SCTP sender, applied on import (aiortc 1.15).
+
+aiortc counts the bytes in flight and sends nothing new while that count is at
+or above the congestion window. A chunk the peer acknowledged in a gap block is
+marked `_acked` and taken out of the count. If the T3 timer then expires, every
+chunk still queued is sent again, that one included, and goes back into the
+count with `_acked` still set. When the cumulative ack finally covers it, the
+SACK handler skips it because it reads as acknowledged already, and its bytes
+stay counted for the life of the association.
+
+Each such loss leaks a chunk. On a lossy path (a phone on Wi-Fi) the leak grows
+past the window, which T3 itself keeps small. From then on the node sends
+nothing on that connection: nothing is outstanding, so no timer runs to unstick
+it, and the association still reads as established. The peer keeps talking and
+the node keeps answering into a queue that never moves. Live symptom: the photo
+backup stalled after a few dozen photos, its slot granted and the grant never
+delivered (docs/MESHBAY_DESIGN.md §9.12).
+
+The fix is the invariant the code assumed: a chunk being sent again is in
+flight, so it is not acknowledged. `test_sctp_fix.py` replays the sequence
+against aiortc itself.
+"""
+
+from aiortc.rtcsctptransport import RTCSctpTransport
+
+
+def _flight_size_increase(self, chunk) -> None:
+    chunk._acked = False
+    self._flight_size += chunk._book_size
+
+
+RTCSctpTransport._flight_size_increase = _flight_size_increase