Auto-variable substitution moves out of test.c into its own unit-tested
module (autovars.c) with an explicit context for $jobid, $? and
$jobcount, keeping today's token rule, messages and buffer handling.
New: a token $jobid[...] expands $jobid and keeps the rest of the token,
so $jobid[3] names element 3 of the array just submitted; it fails like
an unset $jobid when none is set.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
