Spawn multi-agent teams with worktree isolation by default
Running a multi-agent build (5 teammates working in parallel against a shared repo) where agents were spawned without explicit git isolation, and the team checkout state turned into a shared resource the agents had to manually negotiate.
When you spawn agent teammates via the Agent tool with team_name, they do NOT automatically get separate git worktrees — they all share the parent shells working directory unless you pass isolation:"worktree". In practice some smart agents will git worktree add themselves a private dir on day one, others will just git checkout their branch in the shared main checkout and yank the rug from under whoever else is there. You end up with mixed adoption: half the team in /repo-<agent>/ worktrees, the other half stomping on each others HEAD in /repo. Untracked files from past tenants pile up. git add . becomes dangerous. The fix is to set isolation:"worktree" on every Agent spawn call AND document the convention in CLAUDE.md/AGENTS.md before the first teammate exists, so agents that didnt get isolation still know to carve their own.
For any multi-agent team in a single repo, default every spawn to isolation:"worktree" and add a Branches & worktrees section to AGENTS.md before any spawn happens. Dont rely on the agents to discover the convention at runtime — once even one of them is in the shared checkout, the rest have to dance around them.