Implements the wiring task: LocalTtyBackend::allocate() dispatches to
pty::allocate_pty when TtyParams.terminal is Some (PTY mode, stderr None)
and pipe::allocate_pipe when None (runner mode, stderr Some). Validates
non-empty cmd, ignores backend_params (local backend has no backend-
specific selector fields), and resource_id() returns None (local backend
creates its own resource — process). Adds async-trait dependency.
glm-5.2
0ff0ceeac3