fix(session): ignore balanced no-step turns

packages/core/session/src/index.ts

@@ -31,14 +31,24 @@ export { foldSurface, isAppendSurfaceEvent, isReplacementSurfaceEvent, isSurface
 export { canonicalHeader, foldRequestHeader, headerEquals } from './request-header.ts'
 
 /**
- * Find the latest completed model turn in an event sequence.
+ * Find the latest closed turn that entered at least one model step, ignoring
+ * balanced no-step turns produced by rejection, empty input, or cancellation.
  * @param events - session events, or an owned suffix, to inspect.
- * @returns the latest turn end, or `undefined`.
+ * @returns the latest matching turn end, or `undefined`.
  */
 export function findLastMessageTurnEnd(
   events: readonly SessionEvent[],
 ): SessionEvent<'turn/end'> | undefined {
-  return events.findLast(event => event.type === 'turn/end')
+  const steppedTurns = new Set<number>()
+  let latest: SessionEvent<'turn/end'> | undefined
+  for (const event of events) {
+    if (event.type === 'step/start') {
+      steppedTurns.add(event.data.turn)
+      continue
+    }
+    if (event.type === 'turn/end' && steppedTurns.delete(event.data.turn)) latest = event
+  }
+  return latest
 }
 
 declare module 'cordis' {

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

@@ -6,11 +6,28 @@ import SessionStore, {
   Session,
   SessionEvent,
   SessionId,
+  findLastMessageTurnEnd,
   snapshotSessionEvent,
 } from '@deepseek-ai/dsh-session'
 import type { CreateSessionOptions, SessionEventType, SessionHeader, SessionSurface, TodoItem } from '@deepseek-ai/dsh-session'
 
 describe('Session', () => {
+  it('finds the latest closed turn that entered a model step', () => {
+    const session = new Session(SessionId('last-message-turn'))
+    session.append('turn/start', { turn: 1 })
+    session.append('turn/end', { turn: 1, reason: { kind: 'blocked' } })
+
+    expect(findLastMessageTurnEnd(session.events)).toBeUndefined()
+
+    session.append('turn/start', { turn: 2 })
+    session.append('step/start', { turn: 2, step: 1 })
+    session.append('step/end', { turn: 2, step: 1 })
+    session.append('turn/end', { turn: 2, reason: { kind: 'max-tokens' } })
+
+    expect(findLastMessageTurnEnd(session.events)?.data)
+      .toEqual({ turn: 2, reason: { kind: 'max-tokens' } })
+  })
+
   it('exposes one stable readonly surface view', () => {
     const session = new Session(SessionId('surface-view'))
     const surface = session.surface