refactor agent pre-step inbox lifecycle

packages/core/session/src/types.ts

@@ -167,9 +167,9 @@ export type RequestHeaderReason = 'initial' | 'resume' | 'change'
  */
 export interface SessionEventMap {
   /**
-   * Opens turn `turn`. Every turn begins when the loop admits queued input;
-   * the following identified `user/message` event or batch records the
-   * admitted input.
+   * Opens turn `turn`. Every turn begins after the loop claims queued input
+   * and accepts the pre-step result; the following identified `user/message`
+   * event or batch records the messages entering the step.
    */
   'turn/start': { turn: number }
   /**
@@ -187,9 +187,8 @@ export interface SessionEventMap {
    * A user-role message on the model-visible surface: a direct human prompt
    * (the queued message claimed for this turn), a synthetic `agent.inject()`
    * context (file-change notices, subdir AGENTS.md, skill content, cron
-   * notifications, …), or an admitted goal continuation round. All three
-   * project their `content` verbatim; `source` tells them apart. An idle
-   * injection may append this event between turns without running the model.
+   * notifications, …), or an entered goal continuation round. All three
+   * project their `content` verbatim; `source` tells them apart.
    */
   'user/message': UserMessage
   /** Raw stream chunk — token-level replay fidelity. */