The implementation of System-G.
Verification is opt-in. Pass stackqldoc.WithVerifier(v) to Open or
OpenRegistry, where v is constructed by the shared
github.com/stackql/stackql-provider-registry/signing/pqsig.NewVerifier.
Its default trust store is embedded; private registries can supply an explicit
kid to hex ML-DSA-65 public-key map.
Provider metadata, service documents and cross-document operation references
are authenticated before parsing. Missing/invalid signatures and unknown keys
fail closed with the document path. Verified reads bypass the shared parse cache.
No legacy certificate or .sig fallback exists.
For facade plans, set Args.DocumentVerifier; for discovery and table/view
metadata, pass stackqldoc.WithVerifier(v) as the optional document option.
Omitting the verifier preserves existing unverified behavior. Document mutation
and patching invalidate signatures; re-sign patched trees before verified use.
This does not add remote archive download or extraction verification.