Function handle_shell_input 

pub(super) async fn handle_shell_input(
    __arg0: State<AppState>,
    __arg1: Json<ShellInputRequest>,
) -> impl IntoResponse

POST /api/v1/shell/input — write text to a running shell’s stdin (Phase 3b).

Appends a newline so single answers like “y” work without the caller needing to know the line discipline. Returns { written: false } if the shell is not running or the write fails (e.g. the process closed its stdin).