function-orchestrator code can be found at https://gerrit.wikimedia.org/g/mediawiki/services/function-orchestrator
Look for T296676 under src/.
Currently, when validation in the orchestrator fails, it surfaces a stock error. This error should be the Z5 produced by the validator's error formatter. The errorFormatter can be found under function-schemata/javascript/src/errorFormatter.js.
For more context, consult the AJV documentation on errors.
Ideally, we would surface only the errors whose instancePath is longest, as these are likely to be the "real" errors. This work has been de-scoped from this task and moved to T301494: Filter validation errors to avoid over-loading the user with too many overlapping/duplicative errors instead.