solar-return-1.0.0 targets the saved natal tropical geocentric Sun longitude. It brackets the recurrence at twelve-hour intervals and refines the crossing by bisection until the time interval is below one millisecond.

Deterministic contract

• Exactly one recurrence must be isolated inside the requested calendar year.
• The solver returns UTC and selected-zone civil timestamps, target and calculated Sun longitude, residual arcseconds, iteration count, and bracket width.
• Swiss Ephemeris calculates all seven traditional planets, speeds, exact angles, and true solar altitude at the solved instant.
• Whole Sign places and sect are derived from the selected return location.
• Traditional return-to-natal contacts compare two preserved planet sets and never merge their houses.

Regression evidence

The engine fixture freezes a natal Sun target and return year, requires sub-milliarcsecond residual, verifies deterministic repetition and all seven planets, proves that two locations retain the same exact instant while producing different angles, and rejects an invalid IANA timezone.

Interpretive boundary

This version governs recurrence and chart geometry only. It does not prescribe annual-event outcomes, a return-chart favorability score, relocation outcomes, return-specific Lot meanings, automatic profection synthesis, or a composite chart.