Constant EVENT_BTW_ANSWER_CHUNK 

pub const EVENT_BTW_ANSWER_CHUNK: &str = "btw_answer_chunk";

Fired by the /btw slash command’s one-shot side-question turn (server/agent_handlers/side_question.rs, AskSideQuestionCommand) — one event per AgentEvent translated from the throwaway turn’s stream-json output (same ClaudeTranslator the drone Agent block runner uses, agents/translator/claude.rs), plus a final event with "done": true when the turn completes (successfully, with an error, or via a timeout/no-response fallback).

Scoped block:<source_block_id>:btw:<request_id> — the block id of the PANE THAT ASKED, not the throwaway block the turn actually ran on (that one is never surfaced, is deleted when the turn ends, and nothing is ever subscribed to its scope). request_id is the UUID AskSideQuestionCommand mints and returns, so two concurrent /btw asks from the same pane get independently-scoped streams. Payload: { "blockId": "<source_block_id>", "requestId": "<request_id>", "event": <AgentEvent JSON>, "done": bool }. persist: 0 — a /btw overlay is transient UI, not conversation history, so a pane that wasn’t subscribed while it ran has nothing worth replaying.