# Errors only the running app or a build raises

The running app reports three events of its own, never compile errors:

- `runtime.unhandled_fault`: a defect or fault reached the boundary, and
  the client gets `internal_fault`;
- `runtime.outcome_unknown`: a change may or may not have been saved;
- `runtime.startup_failed`: the app couldn't start.

[Logging](logging.md) says what each logs.

`jadpo build` refuses features the compiler checks but can't generate
yet, with `toolchain.target_*` errors. `jadpo check` reports the same
errors, so a project that passes `check` also builds. [Identity](identity.md)
asks the same of a protected route in an app with no sign-in set up.