Add Rust telemetry backend (bevo-rust) for Angelique

[Copilot]

Python's GIL prevents true concurrency in the existing telemd/ backend, making it unsuitable for high-frequency CAN telemetry. This replaces it with a Rust implementation using the lhre-2026 daemon-based architecture.

Structure

Two binaries under bevo-rust/, communicating over a Unix socket:

• publishd — connects to MQTT as BEVO-Angelique, optionally syncs packet_id from server via client-connections/server-communication handshake, writes startup semaphore, then forwards length-prefixed protobuf frames from cand to the angelique topic
• cand — waits for semaphore, reads CAN frames from can0 (or UDP mock via CAND_USE_MOCK=1), decodes into AngeliqueSensorData protobuf at configurable rate (default 100 Hz), broadcasts over Unix socket to all connected clients

CAN Decoding

Field mappings are ported 1:1 from telemd/core/field_mappings.py as a hardcoded match on CAN ID — no JSON config needed. The CellAggregator mirrors Python's CellDataAggregator, accumulating voltage (0x370–0x392) and temperature (0x470–0x486) frames and computing running averages:

// 0x370–0x392: cell voltages → diagnostics.cells_v + pack.avg_cell_v
if (0x370..=0x392).contains(&can_id) {
    if let Some((all_v, avg_v)) = cell_agg.process_voltage(can_id, payload) {
        data.diagnostics.get_or_insert_with(Default::default).cells_v = all_v;
        data.pack.get_or_insert_with(Default::default).avg_cell_v = avg_v;
    }
    return;
}

Proto

bevo-rust/proto/template.proto is a copy of telemd/protobuf/template.proto with package angelique; added for correct prost codegen. Compiled at build time via prost-build.

Concurrency model

Each daemon runs three threads: CAN reader → frame decoder/proto updater (shared Mutex<AngeliqueSensorData>) → IPC broadcaster. The outbound MQTT queue drops frames on overflow rather than back-pressuring the encoder.

Environment variables

Variable	Default	Description
CAND_USE_MOCK	0	Use UDP mock socket instead of can0
CAND_CAN_INTERFACE	can0	CAN interface name
CAND_PUBLISH_HZ	100	Encode/broadcast rate
PUBLISHD_MQTT_HOST	192.168.1.109	Broker address
PUBLISHD_MQTT_PORT	1883	Broker port
PUBLISHD_REQUIRE_SERVER_PACKET_ID	0	Block until server returns packet_id