fix review findings: correct whenIdle live-consumer claim in the stop-surface RFC

The retained-whenIdle paragraph claimed "live consumers (the ACP bridge's settle
points)", but `packages/ui/acp/src` has no whenIdle() call — the bridge owns its
agents and tears them down via AgentHandle.dispose(). whenIdle()'s live consumers
are ACP and agent TESTS awaiting settlement through the public seam. State that.

docs/rfc/implemented/simplification/2026-06-20-public-agent-stop-surface.md

@@ -16,7 +16,7 @@ The extra surface area made the loop carry a public verb that is mostly a teardo
 
 Keep `cancel()` as the only public *stop* primitive on `Agent`. Lifecycle owners use `AgentHandle.dispose()` to stop and unregister an agent; non-owners use `cancel()` to abandon current and queued work. The implementation keeps a private abort controller, but it is not part of the plugin-facing `Agent` contract.
 
-`whenIdle()` is **retained** as the public quiescence-observation primitive (resolve once the agent settles out of `running`, resolve immediately when already idle, await the loop exit when disposed). It is not a stop verb; it is how a non-owner observes the stop *completing* without disposing the agent, and it has live consumers (the ACP bridge's settle points).
+`whenIdle()` is **retained** as the public quiescence-observation primitive (resolve once the agent settles out of `running`, resolve immediately when already idle, await the loop exit when disposed). It is not a stop verb; it is how a non-owner observes the stop *completing* without disposing the agent. Its live consumers are ACP and agent tests that await settlement through this public seam (`packages/ui/acp/tests`, `packages/core/agent-loop/tests`); the production ACP bridge owns its agents and tears them down through `AgentHandle.dispose()`, so `packages/ui/acp/src` itself has no `whenIdle()` call.
 
 Delete public `abort()`, the tests that exercise it as standalone API, and the docs that describe step-only abort as an embedding feature. Empty-queue abort tests migrate to `cancel(reason)` where they still prove cancellation behavior; tests whose subject is the loop's internal `AbortController` behavior drive that controller directly via an in-package typed cast to the private field; tests that only pin the removed no-arg `abort()` default go away with the method. The disposer remains async and still waits for the loop to stop.