scripts: rerun_ci.sh — re-fire a PR's CI without the web button

Gitea 1.24 has no rerun API and the web button needs Grant's SSO identity.
Guarded branch rewind that the next sync undoes; restores the branch itself
on timeout. Used today for eternitas #166 and windy-mind #131 after the
Veron IO stall.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/RUNBOOK-VERON.md

@@ -152,3 +152,16 @@ disqualifying the moment a stranger depends on it. **The trigger is not a date
 it is the first external push.** Move the control plane to a dedicated VPS (not
 Kit 0), keep Veron 1 as the runner. It is an rsync, a Postgres dump and three
 DNS record edits.
+
+## Re-run a PR's CI (Gitea 1.24 has no rerun API)
+
+```bash
+ssh wg-veron
+cd /srv/windygit/src && bash scripts/rerun_ci.sh <repo> <branch> <github-head-sha-prefix>
+```
+Moves the Windy Git branch back one commit; the next sync force-pushes the
+GitHub head again and Gitea re-fires every workflow for that event on the same
+commit. Guarded: refuses unless the branch is at the given sha, waits for a
+sync that starts AFTER the rewind, restores the branch itself on timeout.
+Don't use the web "Re-run" button: it needs a hub-SSO session as windyadmin,
+which is Grant's identity.

scripts/rerun_ci.sh

@@ -0,0 +1,45 @@
+#!/usr/bin/env bash
+# Re-run a PR's (or branch's) CI on Windy Git. Runs ON Veron 1.
+#
+#   bash scripts/rerun_ci.sh <repo> <branch> <sha-prefix>
+#
+# Gitea 1.24 has NO rerun API; the web button needs a hub-SSO session as
+# windyadmin, which is Grant's identity, so we don't use it. Instead: move the
+# Windy Git branch back one commit, let the next sync force-push the GitHub head
+# again, and Gitea fires an ordinary push / pull_request_sync event on the SAME
+# commit. Every workflow on that event re-runs, not only the failed one.
+#
+# Safety: refuses unless the branch is exactly at <sha-prefix> (GitHub's head),
+# never rewinds while a sync is running (a run already past this repo would
+# not push it back), waits for a sync that STARTS after the rewind, and if the
+# branch is not verifiably back at <sha-prefix> by the deadline, restores it
+# itself, so Windy Git is never left behind GitHub.
+set -euo pipefail
+repo="${1:?repo}"; branch="${2:?branch}"; want="${3:?sha prefix}"
+G="sudo docker exec -u git windy-git-gitea-1 git -C /data/git/repositories/windyadmin/${repo}.git"
+
+head=$($G rev-parse "refs/heads/${branch}")
+[[ "$head" == "$want"* ]] || { echo "refusing: ${branch} is at ${head:0:7}, not ${want}"; exit 1; }
+parent=$($G rev-parse "${head}^")
+
+while systemctl is-active -q windygit-sync; do sleep 5; done
+$G update-ref "refs/heads/${branch}" "$parent" "$head"
+mark=$(awk '{print int($1*1000000)}' /proc/uptime)
+echo "rewound ${repo}:${branch} ${head:0:7} -> ${parent:0:7}"
+
+deadline=$(( $(date +%s) + 900 ))
+until [ "$(systemctl show windygit-sync -p ExecMainStartTimestampMonotonic --value)" -gt "$mark" ] \
+      && [ "$($G rev-parse "refs/heads/${branch}")" = "$head" ]; do
+  if [ "$(date +%s)" -ge "$deadline" ]; then
+    $G update-ref "refs/heads/${branch}" "$head" "$($G rev-parse "refs/heads/${branch}")" || true
+    echo "TIMEOUT: restored ${branch} to ${head:0:7} by hand; NO new run fired"; exit 1
+  fi
+  sleep 10
+done
+echo "restored by sync: ${branch} = ${head:0:7}"
+sleep 5
+~/bin/wg-q <<SQL
+select ar.index, ar.workflow_id, ar.event, ar.status, to_char(to_timestamp(ar.created),'HH24:MI:SS')
+  from action_run ar join repository r on r.id = ar.repo_id
+ where r.name = '${repo}' and ar.commit_sha = '${head}' order by ar.id desc limit 6;
+SQL