refactor(agent): complete inbox lifecycle migration

packages/core/session/src/index.ts

@@ -30,6 +30,17 @@ export type { SessionSurface, SurfaceFoldReplacement, SurfaceFoldResult } from '
 export { foldSurface, isAppendSurfaceEvent, isReplacementSurfaceEvent, isSurfaceEvent, isSurfaceEligibleType } from './surface.ts'
 export { canonicalHeader, foldRequestHeader, headerEquals } from './request-header.ts'
 
+/**
+ * Find the latest completed model turn in an event sequence.
+ * @param events - session events, or an owned suffix, to inspect.
+ * @returns the latest turn end, or `undefined`.
+ */
+export function findLastMessageTurnEnd(
+  events: readonly SessionEvent[],
+): SessionEvent<'turn/end'> | undefined {
+  return events.findLast(event => event.type === 'turn/end')
+}
+
 declare module 'cordis' {
   interface Context {
     sessions: SessionStore

packages/core/session/tests/invariant.spec.ts

@@ -188,6 +188,12 @@ describe('session-log invariants', () => {
     skipped.append('step/end', { turn: 1, step: 1 })
     expect(() => skipped.append('step/start', { turn: 1, step: 3 }))
       .toThrow(/expected step 2 in turn 1, got 3/)
+
+    expect(() => skipped.append('turn/end', {
+      turn: 1,
+      step: 0,
+      reason: { kind: 'completed' },
+    })).toThrow(/expected last step 1, got 0/)
   })
 
   it('requires step-scoped stream and tool events to name the open step', async () => {