El Nino Watch
Each history point records the engine version; points from before the 24 Sep 2026 audit are annotated.
Data and trust
`/api/local/history` rows are {evaluated_at, level, level_key, engine_version, note?}. Version 3 (from 24 September 2026) labels every value as observed / forecast / model analysis / reanalysis / bulletin. Rows written by version 2 keep their level (it was computed with the same thresholds) and carry a note saying that engine did not label forecasts.
Limits. The history keeps the last 1000 points (a new point when the level changes, otherwise every 30 minutes).
The level line is continuous across versions; the note only warns that older explanations may have called a forecast date 'observed'.
Nothing in the history is rewritten after the fact, and nothing misleading is shown without a warning.