Why: I1 WP2 - one explicit action field outranks the four legacy
action keys (Handler, metadata.blueprint, command-id, workflow
IntentID) so hosts migrate to a single derivation path.
Evidence: go vet clean; go test ./... all ok, including declared
action winning the Start command and kind/id validation rejections.
Impact: IntentSpec gains Action (command/workflow/blueprint/handler);
Candidate carries it through; actionOf prefers it, then blueprint,
then Handler, then auto. Legacy keys keep working.
Refs: Documents proposal 2026-10-07-agent-stack-n1q1i1-plans.md I1 WP2