RFC-0088: Online Semantic Validation

[meaningforger]

Summary

Propose RFC-0088: Online Semantic Validation. This is a documentation-only RFC for the next Metis Core priorities.

The RFC defines the initial scope, proposed CLI and data contracts, compatibility boundaries, rollout, and observable acceptance criteria. All new commands and APIs are proposed, not implemented.

Scope and priorities

• Keep each semantic query bound to one DataSource.
• Preserve the existing offline s2s boundary and production service/Runner authority.
• No federation implementation or change to the public attribution interface.
• Owners and final RFC numbering are assigned during review.

Verification

• Repository documentation-link check passed against the current main checkout with the three proposed documents.
• Markdown structure, fenced JSON/YAML examples, and whitespace checks passed.
• No runtime behavior or implementation tests are changed.