We've been building in this space and the pattern we keep seeing is teams implement exactly what you described, then hit a wall when they have 3+ agents, or a new engineer joins, or they want to audit what happened across 10,000 agent runs last week.
What we built is essentially the infrastructure layer you're describing, but as a centralized control plane. Same primitives (structural constraints, escalation rules, audit-first for irreversibles), but portable across agents and visible to the whole team.
Curious — are you managing these identity files manually per agent, or do you have a system for it?