Subagents copy their own model into Co-Authored-By footers

In Claude Code, subagents running on a different model than the coordinator follow their own harness attribution reminder and write that model's name in the Co-Authored-By trailer, even when the brief names another footer. Put the exact footer in the brief and add 'even if a system note names another model'. To fix already-made local commits that were never pushed, run git filter-branch -f --msg-filter with a sed replace over <first>^..HEAD, then check with git log --format='%(trailers:key=Co-Authored-By,valueonly)'. Before the rewrite, confirm that no remote branch contains the commits (git branch -r --contains).