Count batched failure notices in browser validation

Why: One system reminder can contain multiple failed child notices, so the browser test must wait for the whole batch rather than one message per child.

Evidence: The first post-merge HTTP/Playwright run failed only at this false one-to-one assumption; all six task-owned browser cases passed after counting notice entries in the persisted reminder.

Impact: Test-only correction; no production UI behavior change.

Refs: U3 r0.4 Task 6 review closure

e2e/work-checkpoints.playwright.ts

@@ -33,9 +33,11 @@ async function waitForFailureNotice(request:any,seed:any){
   if(!response.ok())return false
   const current=await response.json()
   const children=current.runs.filter((r:any)=>r.kind==='subagent')
-  const notices=current.messages.filter((m:any)=>m.role==='system'&&m.parts?.some((p:any)=>p.type==='text'&&p.text?.includes('后台子代理「')))
+  const noticeText=current.messages.filter((m:any)=>m.role==='system').flatMap((m:any)=>m.parts??[])
+   .filter((p:any)=>p.type==='text').map((p:any)=>p.text??'').join('\n')
+  const noticeCount=(noticeText.match(/后台子代理「/g)??[]).length
   const noticeRuns=current.runs.filter((r:any)=>r.kind==='conversation'&&r.id!==seed.sendRunId)
-  return children.length>0&&notices.length>=children.length&&noticeRuns.length>=children.length&&
+  return children.length>0&&noticeCount>=children.length&&noticeRuns.length>0&&
    noticeRuns.every((r:any)=>['completed','failed','interrupted'].includes(r.status))
  }).toBe(true)
 }