Delete the local branch when a merged worktree is cleaned up

[saibotma]

Problem

Worktree cleanup deliberately keeps branches so that resuming a thread can recreate its checkout. That makes sense for inactive or unchanged worktrees, but not once the pull request is merged. Its content is then in the target branch, and the host has usually deleted the remote branch, so the local branch has nothing left to offer. With one worktree per thread, these merged branches pile up in every project, and we delete them by hand. Squash merges make that tedious, because git branch -d refuses them and each branch needs a manual check before git branch -D.

Proposal

When Delete merged worktrees removes a worktree, also delete its local branch, possibly behind its own toggle such as Also delete merged branches. Delete it only when all of these hold:

• A fresh read shows the linked pull request as merged, and its head commit equals the local branch tip. This is the same evidence [Bug]: Merged-worktree cleanup retains worktrees after squash merges #14742's triage proposes for recognizing squash merges.
• No other worktree or thread uses the branch.
• The worktree itself was eligible for removal (no uncommitted changes, no active session).

Resuming such a thread would start a fresh worktree from the default branch, or offer to.

Related

• [Bug]: Merged-worktree cleanup retains worktrees after squash merges #14742: recognizing squash merges in merged-worktree cleanup (same merge evidence)
• Review and act on working trees, branches and remotes from a Version Control panel #15187: manual branch actions in a Version Control panel
• [Feature]: Clean up worktrees for settled threads without deleting history #6856: worktree cleanup for settled threads