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swarm-house/docs/adr/ADR-0003-sync-derived-state-only.md
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docs: record architecture decisions (ADR-0001..0009) and operations knowledge
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2026-07-09 11:41:05 +01:00

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ADR-0003: Sync derived state only; raw telemetry stays local

Status

Accepted (2026-07-08)

Context

Each drone produces high-rate sensor telemetry and on-board video detections — far more than the mesh can carry. But peers only need enough to coordinate flight: where everyone is, where they are heading, what was detected. Pushing raw feeds across the air would saturate the radio and drain batteries for data nobody reads in flight.

Decision

Only derived state crosses the air — position, attitude, detections — as small pub/sub broadcasts (~5 Hz). Raw telemetry stays on local NVMe until the drone lands, then travels to the warehouse during offload (ADR-0002). The design is event-driven: new derived data triggers downstream action through hooks; nothing polls asking "anything new yet?".

Consequences

  • Air bandwidth scales with the number of peers and the broadcast rate, not with sensor resolution.
  • The warehouse is the only place with the full picture; in-flight decisions use the local window plus peer broadcasts.
  • Broadcast staleness per peer becomes a first-class health signal (../07-observability.md).
  • What syncs and what does not is specified in ../04-swarm-sync.md.