fix(session): remove duplicated turn-end step

packages/core/session/src/invariant.ts

@@ -87,10 +87,6 @@ function validateEvent(
       if (trace.openStep !== null) {
         fail(`turn/end ${event.data.turn} while step ${trace.openStep} is still open`)
       }
-      const lastStep = trace.nextStep - 1
-      if (event.data.step !== lastStep) {
-        fail(`turn/end ${event.data.turn} expected last step ${lastStep}, got ${event.data.step}`)
-      }
       openTurn = null
       nextTurn += 1
       break

packages/core/session/src/repair.ts

@@ -46,7 +46,6 @@ export const TOOL_OUTCOME_UNKNOWN = 'TOOL_OUTCOME_UNKNOWN'
 export function interruptedTurnClosers(events: readonly SessionEvent[]): SessionEvent[] {
   let openTurn: number | null = null
   let openStep: number | null = null
-  let lastStep = 0
   // Reset at each turn boundary so earlier calls cannot leak into tail repair.
   // Assistant blocks register calls; later tool/call events add provenance seqs.
   const pendingCalls = new Map<CallId, { step: number; callSeq?: number }>()
@@ -55,18 +54,15 @@ export function interruptedTurnClosers(events: readonly SessionEvent[]): Session
       case 'turn/start':
         openTurn = event.data.turn
         openStep = null
-        lastStep = 0
         pendingCalls.clear()
         break
       case 'turn/end':
         openTurn = null
         openStep = null
-        lastStep = 0
         pendingCalls.clear()
         break
       case 'step/start':
         openStep = event.data.step
-        lastStep = event.data.step
         break
       case 'step/end':
         pendingCalls.clear()
@@ -151,6 +147,6 @@ export function interruptedTurnClosers(events: readonly SessionEvent[]): Session
   if (openStep !== null) {
     closers.push({ type: 'step/end', seq: seq++, time, data: { turn: openTurn, step: openStep } })
   }
-  closers.push({ type: 'turn/end', seq: seq++, time, data: { turn: openTurn, step: lastStep, reason: { kind: 'interrupted' } } })
+  closers.push({ type: 'turn/end', seq: seq++, time, data: { turn: openTurn, reason: { kind: 'interrupted' } } })
   return closers
 }

packages/core/session/src/types.ts

@@ -196,14 +196,14 @@ export interface SessionEventMap {
    */
   'turn/start': { turn: number }
   /**
-   * Closes turn `turn` after `step`, the last entered step (`0` when none),
-   * with the {@link TurnEndReason} that ended it. The loop does not await a
+   * Closes turn `turn` with the {@link TurnEndReason} that ended it. A turn
+   * with no entered step has no `step/start` or `step/end`. The loop does not await a
    * flush at turn boundaries: `dsh-session-checkpoint-policy` owns the
    * per-request durability checkpoint, and consumers that read storage after
    * `whenIdle()` flush themselves. Success commits the turn; rejection is
    * reported live and does not prevent later work.
    */
-  'turn/end': { turn: number; step: number; reason: TurnEndReason }
+  'turn/end': { turn: number; reason: TurnEndReason }
   /** Opens step `step` of turn `turn` — one model call plus the tool executions it requested. */
   'step/start': { turn: number; step: number }
   /** Closes step `step` of turn `turn`. */