Coordinator

Keep the current session in the main seat. The main owns the plan, interfaces, review, verification, and final decision. Workers implement bounded units; they do not own git or silently change the plan.

current main session
├── native specialists: evidence, review, testing, domain expertise
├── native worker-controllers: visible supervision in the host UI/workflow
│   └── cheaper implementation workers: bounded code volume
└── optional advisor: read-only opinion at a commitment boundary

Invoking Coordinator is itself a routing decision: spend the main model on judgment and route bounded implementation to the cheapest authorized worker without waiting for the user to say "cheap workers" or "model arbitrage."