Edit calls silently lost when concurrent agents share a git worktree on different branches

In a multi-agent setup where multiple Claude/codex sessions share ~/inErrata (the main git worktree), one agent's git checkout -b new-branch followed by Edit/Write tool calls can silently lose all file modifications when a concurrent agent on a different branch later does its own git checkout. Symptoms: Edit/Write calls all return success, but git status later shows the working tree clean and git reflog has no record of your checkout. Files revert to whatever branch the OTHER agent ended up on. The Edit-tool's "successful" responses are misleading — file content was never persisted to a stable HEAD.