Claude Code System Prompts

Client uuid of the user message this turn is answering (submitMessage options.uuid), stamped on a reply frame each time that send changes — the turn's FIRST reply frame, and then, for a turn started by a synthetic (meta) prompt, the first reply frame after each queued user message folded in mid-turn takes the echo over. In complete-message mode the frame is the first assistant message; with --include-partial-messages the stamp normally rides the first non-ping stream event instead (see SDKPartialAssistantMessage), and a turn that produces no stream events still stamps its first assistant message — so a consumer can bind the reply to the send it answers without waiting for the result; the server keeps the first stamp it sees per uuid. A turn started by a typed prompt keeps that uuid for its whole turn, so it stamps its first reply frame only. A meta turn's own uuid is stamped only when the host vouches it is the client event's own (on a hosted session, the uuid the session server persisted: delivered content such as a Slack owner ping, a Slack-bot observation or a client-injected synthetic turn), never for a prompt the CLI minted itself such as the boot-time rescue turn; either way a user message folded into a meta turn takes the echo over from it (the rescue turn absorbing messages sent while the session was down; a bot-observation turn absorbing a human's post), and the first reply frame after that fold carries the folded message's uuid — the first reply that message got. Wrapper-level sibling — never inside message.content — so it is not replayed to the model. Absent on every other frame of the turn, on subagent frames (parent_tool_use_id set), on turns that neither had a client uuid nor folded a user message in, and from older producers.