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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
Add docs/adr/ with a chronological ADR set reconstructed from the project
history (no orchestrator, one storage format, derived-state sync,
SQL-over-SSH contract, WireGuard beneath SSH, IaC boundaries, non-root
image, runtime data paths, bounded lake scans), an index README, and a
template. Distinguish repo-local ADRs from ecosystem-wide ASRs.

Expand AGENTS.md with a decision-records section and a runtime/operations
guide (service URLs, rebuild workflow, CPU budget knobs). Reference the
ADRs from README, CONTRIBUTING, and the affected design docs, and add an
open question for T1 partition pruning.
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](ADR-0002-one-storage-format.md)). 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`](../07-observability.md)).
- What syncs and what does not is specified in
[`../04-swarm-sync.md`](../04-swarm-sync.md).