chore: add GH commit conventions check

.github/commit-scopes.txt

@@ -0,0 +1,4 @@
+# Allowed commit scopes, one per line (blank lines and lines starting with `#` are ignored).
+# Used by `.github/scripts/check-commit-messages`.
+core
+tests/core

.github/scripts/add-commit-pr-id

@@ -0,0 +1,159 @@
+#!/usr/bin/env bash
+#
+# Copyright (C) 2026  Vates SAS
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+# ==============================================================================
+# Make the title of every commit of the current branch end with ` (#<pr-number>)`.
+# Commits whose title already ends with this ID only are left untouched, so the script can be run
+# several times.
+#
+# Usage: add-commit-pr-id [--force] <base-sha> <head-sha> <pr-number>
+#
+# - `<base-sha>`: base of the pull request to check and modify.
+# - `<head-sha>`: head of the pull request to check and modify.
+# - `<pr-number>`: number of the pull request.
+# - `--force`: replace the existing pull request IDs of the titles.
+#
+# Every trailing ` (#<digits>)` of a title is considered to be a pull request ID. Without `--force`,
+# the commits that already end with another ID are ignored (and listed), the others are rewritten:
+# an ignored commit is probably in the range because the base is wrong, or the range contains
+# commits of other pull requests.
+# ==============================================================================
+
+set -euo pipefail
+
+SCRIPT_DIR=$(dirname "$(readlink -f "$0")")
+readonly SCRIPT_DIR
+
+readonly AMEND_SCRIPT_PATH="${SCRIPT_DIR}/amend-commit-pr-id"
+
+source "${SCRIPT_DIR}/lib/git.sh"
+source "${SCRIPT_DIR}/lib/pr-id.sh"
+
+# ==============================================================================
+
+readonly FORCE_OPTION="--force"
+
+FORCE=false
+ARGS=()
+for arg in "$@"; do
+    if [ "$arg" = "$FORCE_OPTION" ]; then
+        FORCE=true
+    else
+        ARGS+=("$arg")
+    fi
+done
+readonly FORCE
+readonly ARGS
+
+if [ "${#ARGS[@]}" -ne 3 ]; then
+    echo "Usage: $0 [${FORCE_OPTION}] <base-sha> <head-sha> <pr-number>" >&2
+    exit 2
+fi
+
+BASE_SHA=$(resolve_commit "${ARGS[0]}")
+readonly BASE_SHA
+
+HEAD_SHA=$(resolve_commit "${ARGS[1]}")
+readonly HEAD_SHA
+
+readonly PR_NUMBER=${ARGS[2]}
+if ! is_pr_number "$PR_NUMBER"; then
+    echo "Invalid pull request number: \`${PR_NUMBER}\`." >&2
+    exit 2
+fi
+
+# ------------------------------------------------------------------------------
+
+if ! git diff --quiet || ! git diff --cached --quiet; then
+    echo "The working tree has uncommitted changes: commit or stash them first." >&2
+    exit 1
+fi
+
+if [ "$(git rev-parse HEAD)" != "$HEAD_SHA" ]; then
+    echo "\`HEAD\` is not \`${HEAD_SHA}\`: checkout the head of the pull request first." >&2
+    exit 1
+fi
+
+# ------------------------------------------------------------------------------
+
+if ! MERGE_BASE_SHA=$(git merge-base "$BASE_SHA" "$HEAD_SHA"); then
+    echo "No common ancestor between \`${BASE_SHA}\` and \`${HEAD_SHA}\`." >&2
+    exit 2
+fi
+readonly MERGE_BASE_SHA
+
+readonly COMMIT_RANGE="${MERGE_BASE_SHA}..${HEAD_SHA}"
+if [ -n "$(git rev-list --merges "${MERGE_BASE_SHA}..${HEAD_SHA}")" ]; then
+    echo "Merge commits found in \`${COMMIT_RANGE}\`: this script only supports linear history." >&2
+    exit 1
+fi
+
+mapfile -t hashes < <(git log --format=%H "${MERGE_BASE_SHA}..${HEAD_SHA}")
+
+# ------------------------------------------------------------------------------
+
+PR_ID_SUFFIX=$(get_pr_id_suffix "$PR_NUMBER")
+readonly PR_ID_SUFFIX
+
+to_rewrite=0
+to_ignore=0
+for hash in "${hashes[@]}"; do
+    subject=$(git log -1 --format=%s "$hash")
+    if [ "$(with_pr_id "$subject" "$PR_ID_SUFFIX")" = "$subject" ]; then
+        continue
+    fi
+
+    # The title already ends with a pull request ID other than the requested one.
+    if has_pr_id "$subject" && ! $FORCE; then
+        to_ignore=$((to_ignore + 1))
+        echo "Commit ${hash} ignored, it already has another pull request ID: \"${subject}\"." >&2
+        continue
+    fi
+
+    to_rewrite=$((to_rewrite + 1))
+done
+
+if [ "$to_rewrite" -eq 0 ]; then
+    if [ "$to_ignore" -eq 0 ]; then
+        echo "Nothing to do: every commit of \`${COMMIT_RANGE}\` already ends with \"${PR_ID_SUFFIX}\"."
+    else
+        echo "Nothing to do: ${to_ignore} commit(s) of \`${COMMIT_RANGE}\` ignored with another pull request ID, the others already end with \"${PR_ID_SUFFIX}\"."
+    fi
+    exit 0
+fi
+
+# ------------------------------------------------------------------------------
+
+exec_options=()
+if $FORCE; then
+    exec_options+=("$FORCE_OPTION")
+fi
+
+readonly PREVIOUS_HEAD=$HEAD_SHA
+printf -v EXEC_COMMAND '%q ' "$AMEND_SCRIPT_PATH" "${exec_options[@]}" "$PR_ID_SUFFIX"
+readonly EXEC_COMMAND
+
+if ! rebase_output=$(GIT_SEQUENCE_EDITOR=: git rebase --interactive --no-autosquash --exec "$EXEC_COMMAND" "$MERGE_BASE_SHA" 2>&1); then
+    echo "$rebase_output" >&2
+    git rebase --abort || true
+    echo "Rewrite failed, branch restored (previous HEAD: ${PREVIOUS_HEAD})." >&2
+    exit 1
+fi
+
+echo "${to_rewrite} commit title(s) updated with \"${PR_ID_SUFFIX}\" (previous HEAD: ${PREVIOUS_HEAD})."
+if [ "$to_ignore" -ne 0 ]; then
+    echo "${to_ignore} commit(s) ignored because they already have another pull request ID."
+fi

.github/scripts/amend-commit-pr-id

@@ -0,0 +1,63 @@
+#!/usr/bin/env bash
+#
+# Copyright (C) 2026  Vates SAS
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+# ==============================================================================
+# Amend the title of `HEAD` so that it ends with the given pull request ID suffix, and only with it.
+# The title is left untouched if it already ends like that.
+#
+# Usage: amend-commit-pr-id [--force] <pr-id-suffix>
+#
+# - `--force`: replace the pull request IDs already at the end of the title. Without it, a title
+#   that already ends with a pull request ID is left untouched.
+#
+# Run by `git rebase --exec` from `add-commit-pr-id`, once for each commit it replays. It does
+# none of the checks of `add-commit-pr-id`: do not use it directly.
+# ==============================================================================
+
+set -euo pipefail
+
+source "$(dirname "$0")/lib/pr-id.sh"
+
+# ==============================================================================
+
+readonly FORCE_OPTION="--force"
+
+FORCE=false
+if [ "${1:-}" = "$FORCE_OPTION" ]; then
+    FORCE=true
+    shift
+fi
+readonly FORCE
+
+if [ "$#" -ne 1 ]; then
+    echo "Usage: $0 [${FORCE_OPTION}] <pr-id-suffix>" >&2
+    exit 2
+fi
+
+readonly PR_ID_SUFFIX=$1
+
+# ------------------------------------------------------------------------------
+
+subject=$(git log -1 --format=%s)
+if has_pr_id "$subject" && ! $FORCE; then
+    exit 0
+fi
+
+new_subject=$(with_pr_id "$subject" "$PR_ID_SUFFIX")
+if [ "$new_subject" != "$subject" ]; then
+    # Only the first line of the message (the title) changes, the body is kept as is.
+    { echo "$new_subject"; git log -1 --format=%B | tail -n +2; } | git commit --amend --allow-empty --no-verify -q -F -
+fi