Unchecked
Trace an unchecked Command whose mutation handler is absent.What this error means and what can trigger it
UncheckedCommandHandlerMissingError means Command("unchecked", handler) reached runtime without a truthy second argument. The sentinel only opts out of schema validation; it cannot perform the mutation or produce a result by itself.
TypeScript's intended overload requires the handler, although untyped JavaScript, an unsafe cast, or mismatched generated code can still pass an omitted or falsy value to the guard.
Exactly where it triggers
if (is_unchecked(validate_or_handler)) {
throw new UncheckedCommandHandlerMissingError();
}The factory catches, normalizes, and synchronously rethrows the same Error instance at its declaration boundary. No Command effect has run at this point.
For reference, the class itself is declared at modules/svelte-effect-runtime/src/errors.ts L441 @ C14.
Why this is the case
"unchecked" says that SER should trust the caller's input shape. It says nothing about the state change to execute. Allowing the sentinel to flow into the one-argument path would turn a configuration token into an alleged command program.
The dedicated class makes the invalid overload selection visible during module evaluation, before a user action reaches a broken remote export.