chore(release): take the release PR body as a file in bump-version

AGENTS.md

@@ -42,6 +42,22 @@ Commit or amend only on an explicit go-ahead. Draft the message, show it, and wa
 Never push, and never open a PR. I do both myself, opening the PR from the web UI. Hand me the PR
 title and body as a draft and stop there.
 
+## Releasing
+
+1. Write the release notes for users, not reviewers, in a file outside the repo.
+2. Run `vp run bump-version --body-file notes.md --release <type> --yes`, where `<type>` is the
+   release type I give, such as `patch`. It pushes a release branch and opens its PR with the file
+   as the body. Options other than `--body-file` go to bumpp.
+3. If CI reports stale bundle-size claims, run
+   `vp run replace-bundle-size-claims --write README.md package.json` on that branch, commit, and
+   push.
+4. I merge the PR. The release workflow tags the merge commit, publishes to npm, creates the GitHub
+   release, and publishes the book. The notes start with the PR body, followed by the PRs merged
+   since the last tag.
+
+Steps 2 and 3 push, and step 2 opens a PR. They are the only exception to "Never push, and never
+open a PR" above. Run them only on my explicit go-ahead.
+
 ## Writing Style
 
 Code and prose go in separate turns. Finish the code, then edit the `.md` in a turn of its own, and

scripts/bump-version.sh

@@ -1,17 +1,39 @@
 #!/usr/bin/env sh
 # Bumps the version on a release branch cut from the latest main, and opens its PR.
+# Usage: bump-version [--body-file <path>] [bumpp options]. The file becomes the PR body.
 set -eu
 
 git diff --quiet HEAD -- || { echo 'tracked files differ from HEAD; commit them first'; exit 1; }
 
+# Takes --body-file out of the arguments, and passes the rest to bumpp.
+body_file=/dev/null
+n=$#
+while [ "$n" -gt 0 ]; do
+  arg=$1
+  shift
+  n=$((n - 1))
+  case $arg in
+    --body-file)
+      [ "$n" -gt 0 ] || { echo '--body-file needs a path'; exit 1; }
+      body_file=$1
+      shift
+      n=$((n - 1))
+      ;;
+    *) set -- "$@" "$arg" ;;
+  esac
+done
+
+# Read before anything changes, so a missing file stops the release here.
+body="$(cat "$body_file")"
+
 git switch main
 git pull --ff-only
 
 # bumpp only picks the version; the branch is named after it, so it is cut afterwards.
-bumpp --no-commit --no-tag --no-push
+bumpp --no-commit --no-tag --no-push "$@"
 version="$(node -p "require('./package.json').version")"
 
 git switch -c "chore/release-$version"
 git commit -am "chore: release v$version"
 git push -u origin HEAD
-gh pr create --fill --label skip-changelog
+gh pr create --fill --body "$body" --label skip-changelog