Task 9.4: certifyProvider runs the P9 conformance checklist a provider must pass
before backing a channel — declares explicit capabilities, returns providerRef +
recognized outcome (never throws), repeatable/idempotent, tolerates empty payload.
2 tests: SandboxProvider passes; a throwing/no-capability provider fails with the
specific failing checks listed.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
