Repositories initialized with HEAD -> refs/heads/main (the project default) but populated by pushing a repo with a different default branch (golang/go uses master) end up with HEAD pointing at a nonexistent branch. Git clients cannot check out a worktree and warn: "remote HEAD refers to nonexistent ref, unable to checkout". Fix: repoint HEAD at an existing branch when its symbolic target is missing. Prefer refs/heads/main, then master, then trunk; fall back to the lexicographically smallest branch. Heal is idempotent — a detached HEAD, already-valid HEAD, or branch-less repo is left untouched. Heal on every repository load (fixes repos already in the bucket with no re-push) and after successful receive-pack (fixes new pushes immediately). Both call sites are now guarded by ensureHEAD(), which is no-op when HEAD is already valid. Fixes: #99 (clone checkout abort with dangling HEAD warning) Assisted-by: Claude Opus 4.8 via claude.ai/code