ADR-0003 — Real-time streaming (not store-and-sync)

Status: Accepted · Date: 2026-06-14

Context

The coach needs data live during the session, not as a post-training report. The same ESP32 + GPS + IMU hardware can be built two ways — the difference is firmware, not parts: - Streaming: read sensors and immediately push each sample over WiFi → MQTT → backend → WS → tablet (sub-second). - Store-and-sync: log to flash/SD during the session, download afterwards (what cheap consumer trackers do — no live picture).

Decision

Firmware streams every sample in real time. As a safety net it also logs to flash and replays on reconnect, so a brief WiFi dropout doesn't lose data (real-time primary + backup).

Consequences

• + Live coach view; the project's core differentiator vs commercial post-session tools.
• + Flash backlog makes the live stream resilient to field dropouts.
• − Requires the WiFi link + broker + backend + tablet all live during the session; if any drops, it falls back to "after the fact."

Alternatives considered

• Store-and-sync only — rejected: no live view, defeats the purpose.