The agents /chat/abort endpoint and the resumable disconnect handler save a
partial response through saveMessage without saveConvo following, but did not
pass capExpiryToConversation. In an ephemeral deployment with a parent that
already has an earlier active expiredAt, the partial response got a freshly
computed later deadline and outlived its conversation.
Pass the same cap metadata used by the other message-only abort path so the
partial response cannot outlive its parent. If generation later completes, the
normal response-end save re-stamps the message with a fresh deadline.