fix(app): yield before session history ingestion

packages/app/src/context/server-session.ts

@@ -45,6 +45,12 @@ function projectMessageSource(message: Message): SessionMessageInfo[] {
   ]
 }
 
+function yieldToMain() {
+  const scheduler = (globalThis as { scheduler?: { yield: () => Promise<void> } }).scheduler
+  if (scheduler) return scheduler.yield()
+  return new Promise<void>((resolve) => setTimeout(resolve, 0))
+}
+
 function needsOlderTurnRoot(source: readonly SessionMessageInfo[]) {
   const boundary = source.find(
     (message) =>
@@ -530,6 +536,7 @@ export function createServerSession(
       if (!response.data.length) break
     }
     const response = pages.at(-1)!
+    await yieldToMain()
     const source = pages.flatMap((page) => page.data).toReversed()
     const normalized = normalizeSessionMessages(sessionID, source)
     return {