feat: weekly SLO error-budget report #543

[Sulamoney222]

Overview

This PR adds a weekly SLO error-budget Slack report that posts remaining budget percent per service, weekly consumption, a worst-first leaderboard, and a link to the burn-rate dashboard.

Related Issue

Closes #543

Changes

Weekly SLO report

• [ADD] scripts/slo-weekly-report.ts

  • Uses real route objectives from sloMetrics.ts (booking_intent, slots_list, checkout, escrow_listener).
  • Remaining budget via headroom formula (1 − observedErrorRate / errorBudget).
  • Slack blocks with leaderboard, remaining %, weekly consumption %, status labels.
  • Handles empty week (no traffic → 100% remaining), Slack outage (fail loud), exhausted budgets.

• [ADD] ops/dashboards/slo-burn-rate.json

  • Grafana dashboard (uid: slo-burn-rate) for burn-rate panels.

• [ADD] .github/workflows/slo-weekly-report.yml

  • Monday 09:00 UTC cron + workflow_dispatch.

• [ADD] scripts/__tests__/slo-weekly-report.test.ts

• [ADD] docs/slo-weekly-report.md

• [MODIFY] docs/observability.md — brief SLO weekly-report note

Verification Results

npm test -- --testPathPattern=slo-weekly-report --coverage=false
✅ 21/21 passed

Acceptance Criteria	Status
Compute weekly consumption per SLO	✅ Headroom formula + Prom/fallback path
Slack message with remaining budget %	✅ Leaderboard + status labels
Burn-rate dashboard link	✅ Footer link + ops/dashboards/slo-burn-rate.json
Per-service leaderboard	✅ Sorted worst-first
Edge: empty week / Slack outage / exhausted	✅ Covered in unit tests

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