Worktrees based on origin's default branch use the exact remote branch

A worktree is a second working copy of your git repository in its own folder. When Claude Code creates one based on the default branch of origin (your main remote repository), it now looks up that branch with git show-ref, which matches only the exact remote branch name, instead of a looser lookup.

Other changes in the same step:

• The worktree is created from the commit that branch points to.
• If a git command fails, the error now names the actual command that failed.
• If fetching the latest copy of the branch fails, Claude Code still reads the copy of the remote branch it already has, instead of requiring the fetch to succeed first.