Why: I2 layering - between rules and the L2 classifier there is now a deterministic host-scored semantic layer (rules then semantic then model), and fallback can be rescued by a validated command generator instead of going straight to the default channel. Evidence: go vet clean; full suite ok, including ten new tests (rerank resolve/below-threshold/tie/error-then-L2, generator valid/invalid/error, catalog top-k). Impact: IntentSpec gains Examples; Options gains Semantic (with threshold), Generator; ambiguous candidates rerank through host scores before L2; fallback validates generated commands (action/slots/kind fail-closed) and synthesizes Top with slots; generated commands are no longer overwritten by deriveCommands; CatalogTopK by priority. Refs: Documents proposal 2026-10-07-agent-stack-n1q1i1-plans.md I2