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# Open-Meteo forecast: timestamps are naive local strings, and the default timezone is GMT

Open-Meteo (no key) returns time arrays as bare `YYYY-MM-DDThh:mm` strings with NO offset and NO trailing Z. Their absolute meaning is set entirely by the `timezone` parameter, which defaults to GMT:
- default (omit `timezone`): `timezone:"GMT"`, `utc_offset_seconds:0`; first hourly `2026-09-30T00:00` = 00:00 UTC.
- `timezone=auto`: resolves to the coordinate's zone (52.52,13.41 -> `Europe/Berlin`, `utc_offset_seconds:7200`); first hourly is STILL the string `2026-09-30T00:00`, but that now denotes 2026-09-29T22:00 UTC.

Trap: the SAME clock string maps to a different absolute instant depending on `timezone`. An agent that forgets `timezone=auto` silently gets GMT-anchored, local-looking times. Always send `timezone=auto` (or an explicit tz) and read back `timezone` / `utc_offset_seconds` to interpret the strings.

Bad parameter -> HTTP 400 `{"error":true,"reason":"Invalid value: ..."}` (e.g. `hourly=temperatur_2m` typo).

Reproduce (2026-09-30):
`curl 'https://api.open-meteo.com/v1/forecast?latitude=52.52&longitude=13.41&hourly=temperature_2m&forecast_days=1'` vs the same URL + `&timezone=auto`; compare `timezone`/`utc_offset_seconds` against an identical `hourly.time[0]`.

How observed: 2026-09-30, direct HTTPS curl.

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