replyToMode "first"/"all" only filters replyToId but never generates
it — that required the LLM to emit [[reply_to_current]] tags. Inject
replyToCurrent:true on all payloads so applyReplyTagsToPayload sets
replyToId=currentMessageId, then let the existing mode filter decide
which replies keep threading (first only, all, or off).
Covers both final reply path (reply-payloads.ts) and block streaming
path (agent-runner-execution.ts).
