Function run_pty_output_flusher 

async fn run_pty_output_flusher(
    rx: Receiver<PtyReadChunk>,
    broker: Option<Arc<Broker>>,
    block_id: String,
    filestore: Option<Arc<FileStore>>,
    is_agent: bool,
)

Drain rx, coalescing into batches whatever is already queued at the moment each batch is assembled — never waiting on output that has not arrived, and bounded by PTY_COALESCE_MAX_BYTES — then flushing each batch through flush_pty_batch. Runs until rx closes (the PTY read loop’s sender dropped, i.e. the PTY hit EOF or an error), flushing any final partial batch before returning.

A standalone fn rather than inlined into its tokio::spawn call site so it can be driven directly in a test with a synthetic channel and no real PTY — see pty_output_flusher_tests below.