Function terminal_append_request 

pub fn terminal_append_request(
    process_id: &str,
    await_output: &ProcessAwaitOutput,
    authority: Option<&ProcessCompletionAuthority>,
) -> ProcessEventAppendRequest

Build the replay-keyed terminal event append for a completion.

The single source of truth for the terminal event’s type, replay key, and payload shape, shared by every completion path (leased and unleased) across all backends. When authority is supplied — the unleased ProcessRegistry::complete_process path — it is recorded alongside await_output as durable audit evidence (the leased path’s evidence is the lease it releases, so it passes None and the payload is byte-identical to the historical shape). The await_output selector (/await_output) is untouched by the sibling key.