FSP wire format revision and session-layer MMP implementation ...
FSP wire format revision (TASK-2026-0007):
Introduce the FIPS Session Protocol (FSP) wire format with a 4-byte
common prefix [ver_phase:1][flags:1][payload_len:2 LE] replacing the
old 1-byte msg_type dispatch. All session messages share this prefix
with phase-based dispatch (Established, Setup, Ack, Unencrypted).
- New session_wire.rs: FSP constants, header types, parse/build helpers
- SessionMessageType enum: DataPacket (0x10), SenderReport (0x11),
ReceiverReport (0x12), PathMtuNotification (0x13)
- FspFlags (CP/K/U) and FspInnerFlags (SP) for flag management
- SessionSenderReport, SessionReceiverReport, PathMtuNotification
message structs with encode/decode
- FSP send pipeline: 12-byte header as AAD, 6-byte inner header
(timestamp + msg_type + inner_flags), encrypt_with_aad()
- FSP receive pipeline: parse header, extract cleartext coords (CP),
AEAD decrypt with AAD, strip inner header, msg_type dispatch
- Forwarding: transit nodes parse cleartext coords without decryption
- Removed DataPacket struct and associated types
- SessionEntry: session_start_ms, mark_established(), session_timestamp()
- FIPS_OVERHEAD: 144 → 150 bytes (+6 for FSP inner header)
- Design docs updated for new wire format
Session-layer MMP implementation (TASK-2026-0008):
Implement complete session-layer MMP reusing the link-layer algorithm
modules (SenderState, ReceiverState, MmpMetrics, SpinBitState) with
independent configuration and higher report interval clamps.
- SessionMmpConfig: separate config section (node.session_mmp.*)
- MmpSessionState: session-specific wrapper with PathMtuState tracking
- Session-layer constants (500ms-10s report intervals, 1s cold start)
- Parameterized interval methods (new_with_cold_start,
update_report_interval_with_bounds) on SenderState/ReceiverState
- Bidirectional From conversions between link/session report types
- SessionEntry: mmp and is_initiator fields, initialized on Established
- send_session_msg() for reports/notifications
- Per-message RX recording with spin bit state tracking
- Handlers for SenderReport, ReceiverReport, PathMtuNotification
- path_mtu threaded from SessionDatagram envelope through to handlers
- check_session_mmp_reports() tick handler with collect-then-send pattern
- Periodic and teardown operator logging for session metrics
- PathMtuState: destination observes incoming MTU on all session messages,
source seeded from outbound transport MTU, decrease-immediate /
increase-requires-3-consecutive rules
Link-layer MMP fix:
- Stop feeding spin bit RTT samples into SRTT estimator; inter-frame
timing in the mesh is irregular, inflating spin-bit RTT by variable
processing delays; timestamp-echo provides accurate RTT
29 files changed, 602 tests pass, 0 clippy warnings.
04d9fd625d
