usage_rate_band: a dated per-module rate card of volume bands (generic;
SMS packs the first user). resolveUsageRate picks the band by count
(highest min_qty <= count); below the lowest band = under the minimum
order. buildLines resolves price as: explicit per-line override >
tiered rate card > dated price book — so an SMS line prices by count
automatically, a save under 50,000 is refused, preview warns. Rates are
integer paise (0.40=40p), a new card is a new dated set of rows so issued
invoices keep their rate. Owner routes GET/POST /modules/:id/rate-card.
Tests lock the founder card to the paisa: 50k→₹23,600, 100k→₹43,660,
200k→₹80,240, 300k→₹1,06,200 incl 18% GST. Suite 372 green.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Thomas Joise