Calculate an instant Panchang and local solar events

Strict civil snapshot at the requested instant, not automatically at sunrise. Sidereal Lahiri default. Sunrise/sunset belong to the requested local civil date at elevation zero; ambiguous/nonexistent midnight boundaries return 400. No festivals, regional calendar or arbitrary event search. Latitude is restricted to inclusive [-88,88] for the verified solar-event solver domain. Returned solar candidates must satisfy a geometric crossing check; unsupported near-tangent geometry returns 400 instead of invented events. A solar event inside a recorded leap second returns 400 because its local civil timestamp cannot represent second 60. All admitted attempts reserve one standard quota unit; failed or timed-out admitted attempts are not refunded, including unsupported geometry. No automatic retries. Historical mode uses an explicit BCE/CE date object and UT1 conventions. Its response is the versioned historical envelope, not the modern UTC envelope. Read result for calculation fields and metadata for limits and uncertainty.