Fix Codex subagent relinking after session resume - #2539

Actions cache usage is 8.42 GB of 10.00 GB (84%) across 5 entries. GitHub evicts least-recently-used entries without reporting it, so caches are about to start missing. Run `gh cache list --limit 100 --json key,sizeInBytes` to find the job writing oversized entries; a job on a Blacksmith Linux runner should not appear here at all.