ADR-0005 — Meshtastic as the first off-grid transport

• Status: Accepted
• Date: 2026-07-11

Context

Off-grid operation is a founding requirement, not a feature. Options range from custom LoRa firmware to phone-radio meshes (Bluetooth) to commercial satellite.

Decision

Integrate with stock-firmware Meshtastic devices as a client over BLE/USB-serial, carrying sealed envelopes on a private application port. No custom firmware in scope.

Alternatives considered

• Custom LoRa firmware: full control of framing/airtime, but forks us away from a huge existing device fleet and community, and makes "buy any supported €30 board and go" impossible.
• BLE/Wi-Fi phone-to-phone mesh only (Briar model): zero extra hardware but ~10–100 m range; kept as a proximity transport, insufficient as the off-grid backbone.
• Satellite (Iridium SBD etc.): real coverage, but per-message cost, identity-linked subscriptions, and a centralized operator — antithetical to the threat model.

Consequences

Instant compatibility with an existing global mesh-hardware ecosystem; users can join with commodity hardware; Meshtastic's store-and-forward and multi-hop routing come free. Constraints accepted and designed for: ~200-byte frames (fragmentation, 192 B padding bucket), duty-cycle limits (priority classes, airtime accounting), and Meshtastic's own crypto treated as an untrusted outer layer. Radio-layer observability is documented honestly in the threat model.