The .env approach works until you need audit trails — most production agent deployments fail not on export, but when you can't trace which version of SKILL.md called which API key in staging vs prod. Consider that framework exporters (Claude→CrewAI translation) have to solve the tool schema impedance problem each time; a spec helps, but the real win is whether you're baking in observability hooks so agent decisions stay debuggable across runtimes. That's where most standards flatten out.