Synastry JSON Calculator

Produce one validated schema_version: "2.0" calculation artifact, then hand its exact path to $synastry-reading. Keep interpretation out of the calculator artifact.

Prepare the request

Start from references/request.example.json.
Assign two distinct stable subject id values. Include a display name or pronouns only when the user supplied them; never invent an identity, salutation, gender, relationship role, or preferred location.
Resolve each civil date and IANA timezone. For an exact record, also resolve latitude and longitude.
When given only a place name, consult a current authoritative source, choose a country-qualified result, state the selected place, timezone, coordinates, and source, and ask before continuing when the place is ambiguous. Never recall or default coordinates.
Choose one declared time mode for each subject:

Mode	Required birth fields	Calculation boundary
`exact`	`date`, `time`, `time_accuracy_minutes` from 0 through 15, IANA `timezone`, `latitude`, `longitude`	Calculate one instant, houses, angles, derived values when enabled, and overlays when both subjects are exact.
`window`	`date`, same-date `time_window.start` and later `time_window.end`, IANA `timezone`	Sample the closed interval; omit houses, angles, sect, lots, and overlays.
`date-only`	`date`, IANA `timezone`	Sample the complete local civil day with the same restrictions as `window`.

Never convert uncertainty into an exact noon chart. When the user gives an imprecise phrase, ask for a bounded window or confirm date-only instead of inventing endpoints.