fn write_stage2_trigger(writer: &mut Option<File>) -> Result<()>Expand description
Write the stage2\n trigger into the pipe rbnx and soma share
(see spawn_soma_binary). This is a one-shot: soma reads the
line, unblocks its skill-package launcher, and closes its read
end. rbnx-side we drop the writer here — no reason to hold it
open, and closing gives soma an immediate EOF on the (very
unlikely) chance it re-reads.
If we don’t have a writer (soma wasn’t spawned by us, e.g. –skip-system), this is a no-op with a warning: someone else owns soma’s fd and there’s nothing rbnx can meaningfully do.