Catchable

An on_error rule matches these by code. Reported by is the kind of task that produces the code — a rule naming one its task cannot produce is refused at registration.

Code	Reported by	Means
http.timeout	fetch	connected, but no response arrived in time
http.disconnected	fetch	the request went out, the connection broke before a response
pre.timeout	fetch	timed out before the request was written — it never left
pre.error	fetch	failed before the request was written — it never left
result.parse	fetch	the response body was not valid JSON
result.too_large	fetch	the response body exceeded the size a fetch will read
result.invalid	fetch, child	the result did not satisfy the schema declared for it
external.timeout	external	the wait deadline elapsed
external.lost	external	a worker’s claim expired without an answer
only_once.interrupted	only_once	a previous attempt was interrupted — route it, never retry

HTTP status codes

A fetch whose response status is not accepted fails with http.<status> — http.500, http.404. The family is unbounded, so it has no table: match it with a pattern, http.5%.

Terminal

These fail the instance outright. No on_error rule sees one, so none can be caught or retried; they are listed because every failure stores a code and these are what error_code then holds.

Code	Means
engine.definition	the definition is unusable: missing, or it names a task or goto that is not in it
engine.expression	an expression could not be evaluated against this context
engine.config	config could not be resolved from the environment
engine.input	an input did not satisfy the schema declared for it
engine.output	an output did not satisfy the schema declared for it
engine.spawn	spawning children, or arming an external task and reading its answer, failed
engine.collect	collecting a settled batch’s outputs failed
engine.panic	a Go panic escaped this instance’s advance