[agent operator] enforce selection.maxCount when an agent overshoots without force

Prove that agents and headless MCP clients integrate cleanly: writes flow through the same op envelope (actorClass="agent"), cells tint by provider on the dashboard, the human-write-protection gate rejects agent overwrites of human-set fields without force=true, cardinality is enforced on variant pools unless explicitly overridden, FIXED-tier nodes are never modified by the LLM regardless of model behaviour, and the entire pipeline (extract → enrich → evaluate → tailor) runs through the CF Worker fallback when no browser is present. Includes the deterministic request_id contract that makes headless tailoring idempotent.

Proof set for Agent violates selection cardinality (maxCount=1 with 2 actives) — rejected without `force: true`