chore: the pre-push hook refuses unsigned commits for main, as the deploy does

deploy/redeploy.sh deploys main only if every new commit is signed by a key
in deploy/allowed-signers, and finds out after CI. On 2026-10-09 that held
learn.halkyon.eu at v0.2.2 for two days: 37 commits had reached main
unsigned, and every deploy since refused them. tool/check_signatures.sh
applies the same rule to a push, to the commits it brings to main that the
remote doesn't have yet (the list as the pushed commit has it), and
tool/check.sh runs it first when it runs as the pre-push hook: a second,
where the rest takes minutes. CI runs check.sh under its own name and
skips it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MMm7usAo6q9ZZRoPkWjoxi
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

tool/check.sh

@@ -10,6 +10,12 @@
 set -euo pipefail
 cd "$(git rev-parse --show-toplevel)"
 
+# As the pre-push hook, first: commits going to main must be signed as deploying it requires
+# (tool/check_signatures.sh), which takes a moment, where the rest takes minutes.
+if [ "$(basename "$0")" = pre-push ]; then
+  tool/check_signatures.sh "$@"
+fi
+
 if ! git diff --quiet HEAD; then
   echo 'Note: the working tree has uncommitted changes; they are checked too.'
 fi

tool/check_signatures.sh

@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+# Refuses a push to main that brings a commit not signed by a key in deploy/allowed-signers:
+# the rule deploy/redeploy.sh applies before it deploys main, after CI passed. Checked here, a
+# push of an unsigned commit fails on the laptop instead of after CI (it did on 2026-10-09,
+# when 37 such commits had kept learn.halkyon.eu at v0.2.2 since 2026-10-07).
+#
+# tool/check.sh runs it first as the pre-push hook, passing on git's arguments (the remote) and
+# stdin (a line per ref pushed: local ref, local commit, remote ref, remote commit). It checks
+# the commits pushed to main that no ref of that remote has yet. By hand, for what main would
+# bring:
+#
+#   printf 'refs/heads/main %s refs/heads/main 0\n' "$(git rev-parse main)" |
+#     tool/check_signatures.sh origin
+set -euo pipefail
+
+remote=${1:-origin}
+allowed=$(mktemp)
+trap 'rm -f "$allowed"' EXIT
+
+unsigned=''
+while read -r _local_ref local_sha remote_ref _remote_sha; do
+  [ "$remote_ref" = refs/heads/main ] || continue
+  # Deleting a branch pushes no commits.
+  case $local_sha in *[!0]*) ;; *) continue ;; esac
+  # The list as the pushed commit has it; its comment lines match no fingerprint.
+  git show "$local_sha:deploy/allowed-signers" >"$allowed"
+  unsigned+=$(git log --format='%H %G? %GP' "$local_sha" --not --remotes="$remote" |
+    while read -r commit status key; do
+      # G: a good signature; U: good, by a key the keyring doesn't vouch for (the list does).
+      if { [ "$status" = G ] || [ "$status" = U ]; } && [ -n "$key" ] &&
+        grep -qx "$key" "$allowed"; then
+        continue
+      fi
+      echo "$commit"
+    done)$'\n'
+done
+
+if [ -n "${unsigned//[[:space:]]/}" ]; then
+  echo 'Not signed by a key in deploy/allowed-signers, which deploying main requires:' >&2
+  for commit in $unsigned; do
+    git log -1 --format='  %h %s' "$commit" >&2
+  done
+  echo 'Sign them, e.g. git rebase --force-rebase --gpg-sign <the commit before the first>,' \
+    'and push again.' >&2
+  exit 1
+fi