test(session): cover extensible turn endings

packages/session-persistence/session-persistence/src/coordinator.ts

@@ -273,6 +273,7 @@ function migrateLegacyTurnStartEvent(event: SessionEvent, id: SessionId): Sessio
 function migrateLegacyTurnEndEvent(event: SessionEvent, id: SessionId): SessionEvent {
   if (event.type !== 'turn/end') return event
   const data = asRecord(event.data)
+  /* v8 ignore next -- a non-record current envelope cannot match a legacy shape. */
   if (data === undefined) return event
   const malformed = (): never => {
     throw new Error(`session "${id}" contains malformed pre-react-loop turn/end at seq ${event.seq}`)
@@ -328,7 +329,6 @@ function migrateLegacyTurnEndEvent(event: SessionEvent, id: SessionId): SessionE
       break
     }
     default:
-      /* v8 ignore next -- turn-end reasons are merge-extensible beyond the current vocabulary. */
       return event
   }
 

packages/session-persistence/session-persistence/tests/coordinator-contract.ts

@@ -559,6 +559,20 @@ export function runCoordinatorContract(name: string, makeFixture: () => Promise<
             content: [{ type: 'text', text: 'flat steering' }],
           },
         })
+
+        const extendedId = SessionId('current-extended-turn-end')
+        await ctx.sessionPersistence.create(meta(extendedId, WORK))
+        await ctx.sessionPersistence.append(extendedId, [
+          { type: 'turn/start', seq: 0, time: 1, data: { turn: 1 } },
+          {
+            type: 'turn/end', seq: 1, time: 2,
+            data: { turn: 1, reason: { kind: 'extension-reason' } },
+          } as unknown as SessionEvent,
+        ])
+        expect((await ctx.sessionPersistence.inspect(extendedId)).events[1]).toMatchObject({
+          type: 'turn/end',
+          data: { reason: { kind: 'extension-reason' } },
+        })
       } finally {
         await fiber.dispose()
         await fix.cleanup()