Calculate named symbolic solar-arc directions

Symbolic direct solar-arc directions applied uniformly to natal planets and Ascendant/MC, not a physical sky chart. Omitted method and explicit true_solar_arc preserve the predecessor actual tropical apparent-Sun arc. Explicit mean_naibod applies exactly 0.98564733 degrees per elapsed model year in longitude and does not sample a progressed Sun. Input timing matches secondary progressions: target UTC >= birth, fixed 365.2421904-day TT year, civil dates 1800–2200, strict fields/enums/numbers and DST/polar rejection. Sidereal uses the natal-date ayanamsa only. Equal/Whole Sign houses are synthetic from directed Ascendant, with MC independently directed. No relocation, converse/right-ascension arc, MC-derived angle recalculation, aspects, nodes, speeds or arbitrary key. True-Sun evaluation is bounded to 152 progressed TT days and at most 5 Sun intervals of 32 days; mean Naibod uses one constant-rate multiplication.

All plans use one standard quota unit. Each admitted request reserves one monthly usage unit before route validation or engine work; failed or timed-out admitted attempts are not refunded. Do not automatically retry. The mean-Naibod addition has no practitioner sign-off. 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.