# Add-On indicator (SH-184)

Product rule superseding the SH-126 “frozen at create” FE assumption.

## Authority

| Concern                               | Owner    |
| ------------------------------------- | -------- |
| Cutoff math & week-boundary recalc    | Backend  |
| Clear `isAddOn` when schedule cleared | Backend  |
| Audit of every recalculation          | Backend  |
| Display / board overlay               | Frontend |

The frontend **must not** treat `isAddOn` as frozen after create. Create may
send a **hint** (`resolveIsAddOnForCreate` / cutoff preview or unscheduled
manual override). After any schedule patch or clear, FE consumes the
authoritative `isAddOn` returned by the board PATCH (and subsequent board
fetch).

## FE contract

```
Board row / PATCH response:  isAddOn: boolean
Create (hint):               isAddOn = cutoff preview | manual override
Schedule day/week patch:     FE applies returned row.isAddOn (ON↔OFF)
Schedule cleared:            FE expects isAddOn === false from BE;
                             optimistic clear sets isAddOn: false locally
Legacy:                      workOrderType=AddOn(7) without isAddOn ⇒ isAddOn=true
```

## Dependency

Full backend recalculation + audit may land in a separate BE PR. Until then,
FE still maps and overlays whatever `isAddOn` the API returns so the contract
is correct once BE ships.