Receivers hard-cap reassembly at MAX_FRAGMENTS_PER_ID (256), but the
generic send path fragmented packets with no caller cap (0xFFFF), so
broadcast file transfers above ~120 KB were fully transmitted yet
undeliverable. FragmentingPacketSender now caps fragmentation at
MAX_FRAGMENTS_PER_ID and reports failure via a new
TransferProgressEvent.failed flag, which surfaces as
DeliveryStatus.Failed in the UI and as a file_send error in the debug
test hook instead of an indefinite wait.
Adds FragmentingPacketSenderTest and a file_oversize mesh-lab scenario
asserting sender-side rejection.
Debug-only broadcast receiver (app/src/debug) exposes mesh operations over
ADB: scan, connect, Noise handshake, DMs, broadcast, announce, file
send/receive with SHA-256 verification, BLE toggle, state dumps, and raw
packet injection. tools/release_gate/mesh_lab.py orchestrates scenarios
(dm, broadcast, file, file_private, raw) on two live devices and emits
evidence JSON.
