docs/providers.md collects the provider contract that was spread across
comments, callers and per-provider docs: MUST/SHOULD/MAY rules per method,
each tied to the reconciler or GC behaviour it protects, the error taxonomy,
a feature matrix for kubernetes/gcp/kvm with file:line notes, a checklist for
adding a provider, and the known gaps. Linked from architecture.md and
CLAUDE.md.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
