# Decision Record — Slow BACKBEAT Pulse to 1 BPM

- **UCXL**: `ucxl://chorus-agent:arbiter@backbeat:tempo-calibration/*^/decisions/tempo-1bpm`
- **Date**: 2025-10-06
- **Status**: Accepted

## Problem

BACKBEAT pulse instances were emitting beats at 2 BPM by default, keeping the cluster cadence at 30-second intervals. Operations requested a slower system-wide pulse so councils and agents have a full minute between beats while stabilising the swarm elections and WHOOSH rebroadcast loops.

## Options Considered

1. **Just change deployment flags** — override `backbeat-pulse` with `-bpm 1` in compose files. *Pros*: no code changes. *Cons*: min/max validation rejects <4 BPM, mock SDK fallback still emits 2 BPM, and documentation would drift from runtime behaviour.
2. **Adjust runtime control messages** — send tempo change commands after startup. *Pros*: no rebuild. *Cons*: ±10% guard blocks the 2→1 jump, and services would still boot at the faster tempo.
3. **Update defaults and guardrails in code** *(chosen)* — set default/minimum BPM to 1, align SDK degradation cadence, and refresh guides/tests.

## Decision

Implement option 3. The pulse service now defaults to 1 BPM, accepts values down to 1 BPM, and the SDK’s local degradation beats mirror the slower cadence. Reference docs now mark 1 BPM as the default. Regression tests were updated and pass with `GOWORK=off go test ./...`.

## Impact

- ✅ Cluster pulse slows to 60-second beats without runtime overrides.
- ✅ Operators retain the ability to bump tempo up to 24 BPM within safeguards.
- ✅ SDK degradation flows remain consistent with production cadence.
- ⚠️ Deployments that relied on the old 2 BPM default should confirm updated expectations before release.

## Evidence / Links

- Code: `project-queues/active/BACKBEAT/backbeat/prototype/cmd/pulse/main.go`
- SDK fallback: `project-queues/active/BACKBEAT/backbeat/prototype/pkg/sdk/internal.go`
- Docs: `project-queues/active/BACKBEAT/backbeat/prototype/TEMPO-RECOMMENDATIONS.md`, `project-queues/active/BACKBEAT/backbeat/prototype/contracts/docs/tempo-guide.md`
- Tests: `GOWORK=off go test ./...` (module root)