refactor(agent): complete inbox lifecycle migration

packages/core/agent-loop/src/agent.ts

@@ -190,6 +190,7 @@ export class ReactLoopAgent implements Agent {
     } catch (_error) {
       // Reported failures and cancellation are contained at the driver boundary.
     } finally {
+      /* v8 ignore next -- kick owns a running phase until this driver boundary */
       if (this.phase.kind === 'running') {
         this.setPhase({ kind: 'idle', lastTurn: this.phase.turn })
       }
@@ -197,6 +198,7 @@ export class ReactLoopAgent implements Agent {
   }
 
   private async preStep(target: InboxTarget, position: { turn: number; step: number }): Promise<PreparedStep> {
+    /* v8 ignore next -- private callers establish the running phase before proposing a step */
     if (this.phase.kind !== 'running') throw new Error(`agent "${this.id}": pre-step outside running phase`)
     const signal = this.phase.abort.signal
     const claimed = this.inbox.claim(target)
@@ -294,6 +296,7 @@ export class ReactLoopAgent implements Agent {
   }
 
   private async step(assembly: PromptAssembly): Promise<StepEndReason | null> {
+    /* v8 ignore next -- private callers establish the running phase before executing a step */
     if (this.phase.kind !== 'running') throw new Error(`agent "${this.id}": step outside running phase`)
     const { turn, step, abort: { signal } } = this.phase
     signal.throwIfAborted()