Modules

Commands of your own are registered the way the built-in ones are. A module adds them with Command(…) on its builder, named after the module (chapter 18). Host code registers them on CmsApiCommands:

var commands = app.Services.GetRequiredService<CmsApiCommands>();
commands.Register("shop-stock", ctx => {
    var p = ctx.Payload<StockRequest>();
    return ctx.Db.Query<IProduct>().Where(x => x.Sku == p.Sku).Execute().Select(x => x.Stock);
}, readOnly: true);

`CmsApiContext`	Is
`Db`	the store as the caller, in the payload's context
`Root`	the whole store, for checks the server makes on its own behalf; never answer the user from it
`Payload<T>()`	the payload, read from camelCase JSON
`UserId`, `IsAdmin`, `IsInGroup(id)`	who is asking; `IsInGroup` checks direct membership
`Changed(id, typeId, kind)`	adds a node to the `nodes-changed` event once the command succeeds
`StartProcess(start, work)`	starts a process (below)

Throw CmsApiException(status, message) to answer with an error.
readOnly: true marks a command that changes nothing. Only those run for an anonymous caller.
Register replaces any command of the same type, a built-in one included, so give yours names of their own.
CmsApiEvents.Broadcast(name, payload) sends an event of your own to every connection. The SDK hears it with store.channel.subscribe(name, handler).