feature(repo_cleanup): make branch deletion reachable from a cloud session - #278

…ssion

A cloud Claude session — phone or claude.ai/code — can audit branches but
cannot remove one: `git push origin --delete` returns 403 for the session
credential (the proxy logs no relay failure, so it is GitHub's policy, not
egress), and the GitHub tool surface those sessions get has no delete-ref
call at all. Branch cleanup was therefore laptop-only, and it showed: a sweep
on 2026-08-25 found 233 branches across Mind and Brain, 188 of them provably
spent, with nothing able to act on the finding.

A workflow's GITHUB_TOKEN is a different credential, and these repos already
trust it with `contents: write` — dashboard_refresh.yml commits to main with
it. So the sweep now runs inside the repo on Actions, and any surface that can
dispatch a workflow can drive it.

- `bin/branch_sweep.sh` — the executable half of the skill. Classifies every
  remote branch via branch_contribution.sh (never a hand-rolled ahead-count,
  per agent_failure_modes D1/D2) and deletes only what is provably contained.
  Two extra pieces of care:
    * It unshallows first. On a truncated history every ancestry question is
      wrong in the same direction — nothing looks contained — so a shallow
      clone would silently sweep nothing while reporting success. This was not
      hypothetical: the audit that motivated this ran shallow first and read 94
      plainly-merged branches as unmerged.
    * A CONTRIBUTES branch may still be a squash-merge git 2.34 cannot see
      through. It asks GitHub for a merged PR at that exact tip, then falls
      back to proving the squash locally by patch-id. Unproven means kept.
- `.github/workflows/branch_sweep.yml` — dispatch (audit|delete, optional
  limit) plus a weekly audit-only cron; a scheduled run cannot delete whatever
  the cron says. The step summary carries the report, which is the readable
  surface on a phone.
- `tests/test_branch_sweep.py` — known-answer repos for the four gates that
  keep a branch out of the delete set: main, `archive/condemned/*` Gut transit
  refs, open PR heads, and unproven content. The deletions are one push; the
  refusals are the part worth pinning.
- The skill now routes cloud sessions to the dispatch instead of telling them
  the sweep is blocked, and says once that a repo still accumulating merged
  heads has "Automatically delete head branches" off — the setting that stops
  this backlog forming, which no sweep substitutes for.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KwqicJpMqmcT5RVbyNwdKq

CI caught two things the local run could not.

1. The shallow guard tested `-f "$(git -C $REPO rev-parse --git-dir)/shallow"`.
   With `-C`, `--git-dir` comes back *relative* (`.git`), so that path resolves
   against the calling process's cwd — the guard was really asking "is the
   directory I happen to be standing in a shallow clone?". On an Actions runner
   the answer is yes, because actions/checkout is shallow by default, so the
   sweep tried to unshallow a complete repository and died on
   `fatal: --unshallow on a complete repository does not make sense`.

   Now it asks `rev-parse --is-shallow-repository`, the purpose-built predicate,
   which is about the repo named by `-C` and nothing else. Reproduced first: a
   cwd carrying `.git/shallow` makes the old expression true and the new one
   false for the same complete repo.

   Worth noting the failure mode was the safe direction by luck, not design —
   it aborted rather than sweeping on bad verdicts. The next caller might not
   be so lucky.

2. Prerequisite ordering. The gh check ran *after* the fetch/unshallow, so a
   run with no gh rewrote the caller's clone and only then refused. Moved both
   the presence and auth checks above any git mutation: if we are going to say
   no, say it before touching anything.

The test's deliberately-lean PATH gained the coreutils the script actually
calls (dirname and friends); without them the no-gh test was exercising a
missing-dirname crash rather than the refusal it claims to pin.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KwqicJpMqmcT5RVbyNwdKq