Robustness checklist

The behaviours most likely to surprise a first integration, collected in one
place:

• 1m means one month. There is no one-minute range on either time-series
  endpoint.
• Time-series values are strings. Parse the second element of every sample
  pair, including for integer-valued series.
• /dataplane-stats is stateful. One collector only, or use the cumulative
  byte counters instead.
• GET /api/bng/events mutates. One collector, sane interval.
• /setup-wizard/apply always returns 200. Inspect every per-section ok.
• /audit/export degrades to partial. Verify the row count.
• Restore is not transactional. Handle 207.
• An invalid step or limit does not error — it silently falls back to the
  default. Only an invalid range, an unknown metric, and a missing required
  ip return 400.
• Never retry a 403. Honour Retry-After on 429. Re-mint before retrying
  a 401.
• A flat time series may mean sampling stopped, not that the value fell to
  zero. Cross-check health or the scrape liveness.

Boundaries and Stability