Cover the input-validation contract dispatch_run relies on:
- no declared schema → inputs pass through unchanged (regression site
that previously stripped runtime keys like fired_at / last_fired_at
and broke Jinja templates).
- declared schema, valid inputs → passthrough validated.
- declared schema, invalid inputs → DispatchError (uniform exception
type, not raw jsonschema.ValidationError).
Plus the DispatchError exception identity (Exception subclass, message
preserved, isinstance-friendly for the dispatch layer's consumers).
4 tests, pure unit.
Cover the cron + IANA timezone + UTC normalization contract for the
schedule trigger: next-match strictly-after, DST offset shift across
spring-forward, malformed cron / unknown timezone rejection, and the
ScheduleTriggerParams Pydantic gate that surfaces InvalidCronError as
ValidationError at the API boundary.
8 tests, pure unit (no DB, no mocks).
