Both scripts handled an unknown option with `error ...; usage`, and usage()
always ended in `exit 0`:
$ ./scripts/convert.sh --tol codex; echo $?
[ERR] Unknown option: --tol
...usage...
0
so a mistyped flag in CI or a wrapper script read as success. usage() now
takes a status. --help still prints to stdout and exits 0; an unknown
option prints the usage text to stderr and exits 1, the same as a bad
--tool or --division value already does.
convert.sh --help also printed a hard-coded `sed -n '3,28p'`. The option
notes live on lines 33-34, so --parallel and --jobs never appeared, and
--out was only in the synopsis. It now uses USAGE-START/END sentinels, as
install.sh has for a while, and the option list covers --tool and --out.
test-cli-usage.sh checks both scripts: an unknown option exits non-zero
with its name and the usage on stderr and nothing on stdout, --help exits 0
without printing the sentinels, and convert.sh --help describes --tool,
--out, --parallel and --jobs. It fails on main at the first check and runs
in check-tools.yml.
