refactor: replace overloaded surface terminology

packages/core/agent/README.md

@@ -116,6 +116,6 @@ Prefix-stable while an agent's scoped registrations are unchanged. Setup or relo
 - **Ambient identity may outlive liveness** — consumers still check `agent.status`, cancellation, and the owning capability contract before lifecycle-sensitive work.
 - **Inter-agent channels beyond delegation** — shared state, streaming child output, and background/poll semantics remain outside the current synchronous `ctx.subagents` seam.
 - **`agent/session-start` cannot gate startup** — it remains a synchronous, veto-less notification; async composition that must finish before publication belongs in the factory's `setup(agentCtx)` transaction instead.
-- **`cancel()` clears the inbox by default** — it aborts the in-flight turn plus queued and steering work; `cancel(cause, { keepInbox: true })` aborts only the turn and preserves pending items. There is still no step-only abort that keeps the in-flight turn running ([stop-surface Agent Note](../../../.agents/notes/implemented/simplification/2026-06-20-public-agent-stop-surface.md)).
+- **`cancel()` clears the inbox by default** — it aborts the in-flight turn plus queued and steering work; `cancel(cause, { keepInbox: true })` aborts only the turn and preserves pending items. There is still no step-only abort that keeps the in-flight turn running ([stop API Agent Note](../../../.agents/notes/implemented/simplification/2026-06-20-public-agent-stop-api.md)).
 - **Each additional `UserMessage` carries exactly one `MessageSource`** — contributions from several plugins merged onto one tool call collapse under one source, so the message cannot name several producers.
 - **`SessionStartSource` reserves `'clear'`/`'compact'` with no emitter yet** — only `'startup'`/`'resume'` occur until the driving subsystems land (`TODO(compaction)`).