Bill a monthly group class its fee once per month

A monthly group class multiplied its price by the sessions falling in the month,
the same rule private lessons use — so a class priced at 40.00 CAD meeting
weekly was billed 160.00 CAD on the 1st, and no studio could quote the price on
a class card without lying about it.

A group class is now billed its fee once for the month however many times it
meets, which is what the card quotes and what the student ticks to agree to.
Private lessons keep the per-lesson rule: their price is a per-lesson fee, and
that is why the card quotes it per lesson.

The session count still labels the month on the student's payment notice; it no
longer prices it.

Co-Authored-By: Claude Opus 5 <[email protected]>

docs/features/offerings.md

@@ -33,7 +33,7 @@ An offering is anything a student can register for: a private-lesson type (30 or
 - `one_time` — charged once at booking (a single private lesson).
 - `full_term` — charged in full upfront at registration (a weekly private reservation or a year-long group class). See `payments.md`.
 - `weekly` — **not** charged at registration; a pending payment for one lesson's fee is generated **24 hours before each lesson** by the daily billing scan.
-- `monthly` — **not** charged at registration; on the **1st of each month** a single pending payment is generated for every lesson that falls in that month (4 lessons ⇒ 4 × fee).
+- `monthly` — **not** charged at registration; on the **1st of each month** a single pending payment is generated for that month. A **private lesson**'s price is a per-lesson fee, so the month is billed (#lessons in the month) × fee; a **group class**'s price is the monthly fee itself, billed once for the month however many times the class meets in it.
 
 Students see the mode as a **cadence** beside every price on the front end — *at
 booking*, *up front*, *weekly*, *monthly* — and confirm it explicitly before a

docs/features/payments.md

@@ -112,19 +112,15 @@ offering's `billing_mode` in the words the student needs:
 So a lesson type reads `50.00 CAD at booking` in the booking form's type picker,
 and a group class card reads `120.00 CAD up front`. A free offering shows `Free`.
 
-**`monthly` reads differently per offering kind.** A private lesson's monthly
-charge is that month's lessons × the fee, so the fee is quoted **per lesson**
-(`50.00 CAD per lesson monthly`). A group class is enrolled in once, as one
-schedule, so its figure is quoted as it stands (`120.00 CAD monthly`) — see
-`isPerLessonMonthly()` in `assets/js/pricing.js`.
-
-> **Caveat.** `ScheduledBillingRunner::billGroupMonthly()` bills a monthly group
-> class `price × sessions in the month`, the same per-session multiplication used
-> for private lessons — so a class meeting weekly is charged roughly four times
-> the quoted `120.00 CAD monthly` figure. The display deliberately quotes the
-> price as a monthly figure; closing the gap means either billing a monthly group
-> class once per month regardless of session count, or restoring the per-lesson
-> wording for group classes too.
+**`monthly` reads differently per offering kind, because it *bills* differently.**
+A private lesson's price is a per-lesson fee and its monthly charge is that
+month's lessons × the fee, so the fee is quoted **per lesson**
+(`50.00 CAD per lesson monthly`). A monthly group class is priced **per month** —
+`ScheduledBillingRunner::billGroupMonthly()` charges the fee once for the month
+however many times the class meets in it — so its figure is quoted as it stands
+(`120.00 CAD monthly`). The display split is `isPerLessonMonthly()` in
+`assets/js/pricing.js`; the billing split is the one place the monthly rule
+differs between the two kinds.
 
 Before a booking or enrolment can be submitted, the form shows the price again as
 a summary block with a **required agreement checkbox** — the second confirmation,

docs/features/scheduled-billing.md

@@ -6,7 +6,9 @@ payments on a recurring schedule:
 
 - **`weekly`** — one payment per lesson, due **24 hours before** that lesson.
 - **`monthly`** — one payment per calendar month, due on the **1st**, covering every
-  lesson that falls in the month (4 lessons ⇒ 4 × fee).
+  lesson that falls in the month. A **private lesson**'s fee is per lesson, so the
+  month costs (#lessons) × fee. A **group class**'s fee is per month: the class is
+  billed that fee once for the month, however many times it meets in it.
 
 Both apply to **private lessons** and **group classes**. At registration the
 booking/enrolment succeeds with `payment: null` (no payment step); the lesson is
@@ -29,7 +31,7 @@ method resolution, e-transfer freezing, comp auto-pay reused) with a `due_date`
 | **Private weekly** | lesson `start_dt` ≤ now + 24h | 1 × fee | `us_lessons.payment_id` set on the lesson |
 | **Private monthly** | the lesson's month's 1st ≤ today | (#lessons in month) × fee | `payment_id` set on every lesson in the month |
 | **Group weekly** | session (from `Offering::sessionWindows()`) − 1 day ≤ now | 1 × fee | `us_payments.period_key` = session date |
-| **Group monthly** | the month's 1st ≤ today | (#sessions in month) × fee | `period_key` = `YYYY-MM` |
+| **Group monthly** | the month's 1st ≤ today | 1 × fee (a monthly class is priced per month, not per session) | `period_key` = `YYYY-MM` |
 
 - Private lessons dedup on `us_lessons.payment_id IS NULL` — a lesson with no payment is
   unbilled. A monthly group links its earliest lesson via `createForRegistration` and the