Error codes

An error record has error and from for people, and code, path, got, want, fix, class and near for tools. class is fixable (an edit to the data fixes it) or authority (no edit by this author can). The codes below are read from the engine source when the docs are written.

Code	Meaning
arg	an element asks for an arg that has no answer
at	at holds a value that is not a predicate
bare-function	an element is a function without named args (x: …): wrap it as { ... }:
check	a field value fails its type
cycle	an instance appears twice on its own scope path: spawns loops
error	a message from an aspect’s errors key, a failed of, or a component
merge	merge: two different leaves at one path
missing	a required field has no value
missing-param	a stored query is asked without a required parameter
one	one: 0 or 2+ elements
outside-grant	a staged change gives an element outside its grant
program	a change program op is not valid
ref	a field wants an instance ref and got something else
rejected	a staged change was rejected before (its sha is in rejected)
two-answers	one declaration leaf has two different values
unknown-field	an instance sets a field its kind does not declare
unknown-param	a stored query is asked with a parameter it does not take

Errors as data Records, your own checks, and warnings.