ci: daily nix flake update workflow

.forgejo/workflows/flake-update.yml

@@ -0,0 +1,60 @@
+name: flake update
+
+# Daily `nix flake update`; opens a PR only if the lock changed, never
+# merges (mara does, by hand - branch protection requires it anyway).
+# Separate file from ci.yml/coverage.yml for the same reason coverage.yml
+# is: a workflow_dispatch in ci.yml fires every job there.
+#
+# Plain branch + curl POST (not AGit), mirroring mara's own
+# nixos-configuration:.forgejo/workflows/flake-update.yaml - a daily lock
+# bump never updates an existing PR, so AGit's advantage there doesn't
+# apply. Stale PRs just stack; newest lock wins.
+#
+# `PR_BOT_TOKEN` (repo secret) is the `flake-bot` account's write token.
+# Self-signed forge cert: not worked around with `curl -k` - hive-ci.nix
+# already sets SSL_CERT_FILE to a bundle with the hive CA (wiring
+# confirmed; anchor coverage for the swarm forge specifically isn't).
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: "0 3 * * *"
+
+jobs:
+  update:
+    name: nix flake update
+    runs-on: [hive-ci]
+    timeout-minutes: 30
+    steps:
+      - uses: actions/checkout@v3
+      - name: update and open a PR if the lock changed
+        env:
+          PR_BOT_TOKEN: ${{ secrets.PR_BOT_TOKEN }}
+        run: |
+          set -euo pipefail
+          nix flake update
+
+          if git diff --quiet -- flake.lock; then
+            echo "flake.lock unchanged, nothing to do"
+            exit 0
+          fi
+
+          # origin's scheme+host, not a hardcoded forge URL - checkout
+          # already resolved an address this runner can reach.
+          origin_url="$(git remote get-url origin)"
+          scheme="${origin_url%%://*}"
+          host="$(printf '%s\n' "$origin_url" | sed -E 's#^[a-z]+://([^/]+)/.*#\1#')"
+
+          branch="flake-update-$(date +%F)"
+          git checkout -b "$branch"
+          git -c user.name="flake-bot" \
+              -c user.email="git+flake-bot@darkest.space" \
+              commit -am "nix flake update"
+          git push "${scheme}://flake-bot:${PR_BOT_TOKEN}@${host}/hyperhive/hyperhive.git" "$branch"
+
+          printf '{"title":"nix flake update","head":"%s","base":"main"}' \
+            "$branch" > /tmp/flake-update-pr.json
+          curl -sf -X POST \
+            -H "Authorization: token ${PR_BOT_TOKEN}" \
+            -H "Content-Type: application/json" \
+            -d @/tmp/flake-update-pr.json \
+            "${scheme}://${host}/api/v1/repos/hyperhive/hyperhive/pulls"