Two remaining gate failures fixed:
- prefix() now namespaces discriminator.mapping values (ref-STRINGS, not $ref keys)
→ platform DeployJob*/CancelDeploymentJob* no longer dangle.
- referrals was the one spec using cross-file ../shared/errors.yaml refs → inlined
the error responses (BadRequest/Unauthorized/Forbidden/NotFound/InternalServerError)
+ Error schema, rewrote refs local. Self-contained like every other spec.
Exact CI gate: dupIds=0 dangling=0 GATE PASS. Unblocks regenerate-sdks.yml.