Measure planetary house-placement stability across supported systems

Evaluates the ten natal planets across Cosmic Ephemeris's fixed inventory of 24 comparable 12-house systems. Returns exact per-system house assignments, unweighted agreement ratios, tied most-common houses, deterministic placement-equivalence groups, unavailable polar geometries, and an explicit no-fallback guarantee. Gauquelin's 36 sectors are identified but excluded from 12-house comparison. Agreement is descriptive, not a recommendation or claim that a house system is correct. One standard quota unit per admitted request; failed or timed-out admitted attempts are not refunded. Do not automatically retry. 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.