# Feature: Cancellation Cutoff

## Overview
Students may cancel their own lessons online — but not indefinitely close to the
start time. A **cancellation cutoff** closes student-initiated cancellation once
a lesson begins within a configured window. Instructors and studio admins are
never subject to the cutoff: they can cancel a lesson at any time through the
lesson-status and student-management flows.

The window is resolved per lesson:

1. If the lesson's **offering** sets its own cutoff, that value is used.
2. Otherwise the **studio default** applies.

Both values are expressed and computed in **hours**. The studio default is
entered and displayed to the admin in **days** for convenience; a per-offering
override is entered directly in hours (a finer-grained "time").

## Data Model

### Option `us_cancellation_cutoff_hours`
Studio-wide default cutoff, stored as an integer number of **hours**. Defaults to
`24` (one day) when unset. `0` means students may cancel at any time.

### Column `{prefix}us_offerings.cancellation_cutoff_hours`
Nullable `SMALLINT UNSIGNED`. `NULL` means "inherit the studio default"; any set
value (including `0` — cancel any time) overrides it for that offering.

## Resolution & Enforcement
`Booking\CancellationPolicy` owns the logic:

- `cutoffHours(?int $offeringCutoffHours): int` — the offering's override when it
  is a non-negative value, otherwise the studio default.
- `studentMayCancel(string $slotStartDt, ?int $offeringCutoffHours, ?string $now): bool`
  — false once `now` is within the effective cutoff of the slot start. A zero
  cutoff always allows cancellation; unparseable datetimes fail open so a student
  is never trapped by bad data. Comparisons use WordPress-local time
  (`current_time('mysql')`), matching how upcoming lessons are computed.
- `describeCutoff(int $hours): string` — humanises a cutoff for messages
  (whole days as days, otherwise hours).

`Booking\BookingEndpoint::cancel()` (the student endpoint,
`POST /bookings/{id}/cancel`) consults the policy before cancelling and returns a
`cancellation_closed` (HTTP 403) error explaining the window when it is too late.
The instructor status endpoint (`PATCH /bookings/{id}/status`) and
`Auth\StudentActions::cancelLesson()` (studio-admin student view) bypass the
policy entirely.

## Admin Interface
- **Studio Settings → Cancellations**: "Cancellation cutoff (days)" — the studio
  default, entered/displayed in days, stored in hours.
- **Offerings** add/edit form: "Cancellation cutoff (hours)" — an optional
  per-offering override; blank inherits the studio default, `0` allows anytime
  cancellation.

## Implementation
- Service: `Unsupervised\Schedular\Booking\CancellationPolicy`
- Studio default: `Unsupervised\Schedular\Payment\StudioSettings::cancellationCutoffHours()`
  (option `us_cancellation_cutoff_hours`)
- Per-offering value: `Unsupervised\Schedular\Offering\Offering::$cancellationCutoffHours`
- Enforcement: `Unsupervised\Schedular\Booking\BookingEndpoint::cancel()`
- Wiring: `RestRegistrar` constructs `new CancellationPolicy( new StudioSettings() )`

## Tests
- `tests/Unit/Booking/CancellationPolicyTest.php`
- `tests/Unit/Booking/BookingEndpointTest.php` (cutoff cases in `cancel()`)
- `tests/Unit/Payment/StudioSettingsTest.php` (default getter)
- `tests/Unit/Offering/OfferingTest.php`, `tests/Unit/Offering/OfferingRepositoryTest.php`
  (new column round-trips)