delete branch if bump fails

.forgejo/workflows/build.yaml

@@ -24,9 +24,10 @@ jobs:
         env:
           PREEM_PUSH_TOKEN: ${{ secrets.PREEM_PUSH_TOKEN }}
 
-  # nightly-flake-update.yaml opens PRs from flake-update-* branches; if
-  # the build fails on one of those, close it rather than leaving a
-  # broken auto-generated PR around. Scoped to that branch prefix so a
+  # flake-update.yaml opens PRs from flake-update-* branches; if the
+  # build fails on one of those, close it and delete the branch rather
+  # than leaving a broken auto-generated PR around (and so a same-day
+  # rerun can push the branch again). Scoped to that branch prefix so a
   # failing build on a human-authored PR is never auto-closed.
   close-on-failure:
     needs: build
@@ -39,5 +40,9 @@ jobs:
             -H "Content-Type: application/json" \
             -d '{"state": "closed"}' \
             "https://forge.darkest.space/api/v1/repos/mara/nixos-configs/pulls/${{ github.event.pull_request.number }}"
+          curl -sf -X DELETE \
+            -H "Authorization: token ${PR_BOT_TOKEN}" \
+            "https://forge.darkest.space/api/v1/repos/mara/nixos-configs/branches/${HEAD_REF}"
         env:
           PR_BOT_TOKEN: ${{ secrets.PR_BOT_TOKEN }}
+          HEAD_REF: ${{ github.head_ref }}