add set_pr_body and refactor workflow

.github/workflows/changesets-preview-pr.yml

@@ -44,15 +44,11 @@ jobs:
 
       - name: Generate new changelog
         if: steps.change.outputs.core-changeset == 'true'
+        id: changelog
         run: pnpm install && ./tools/ci/format_changelog
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
-      - name: Get release version
-        if: steps.change.outputs.core-changeset == 'true'
-        id: get-release-version
-        run: echo "version=$(jq -r '.version' package.json)" >> $GITHUB_OUTPUT
-
       - name: Create release preview PR
         if: steps.change.outputs.core-changeset == 'true'
         uses: peter-evans/create-pull-request@6d6857d36972b65feb161a90e484f2984215f83e # v6.0.5
@@ -64,12 +60,8 @@ jobs:
           commit-message: "changeset: release preview"
           committer: app-token-issuer-releng[bot] <app-token-issuer-releng[bot]@users.noreply.github.com>
           branch: changesets/release-preview
-          title: "[DO NOT MERGE] Changeset Release Preview - v${{ steps.get-release-version.outputs.version }}"
-          body: |
-            This PR is a preview of the changes that will be included in the next release. Please do not merge this PR.
-            <!--
-            This PR was created by the changesets-release-preview workflow.
-            -->
+          title: "[DO NOT MERGE] Changeset Release Preview - v${{ steps.changelog.outputs.version }}"
+          body: ${{ steps.changelog.outputs.pr_body }}
           draft: true
           labels: |
             release-preview

tools/ci/format_changelog

@@ -38,8 +38,35 @@ EOF
   done
 }
 
+set_pr_body() {
+  # GitHub Issues/PRs messages have a max size limit on the message body payload.
+  # This is the error: `body is too long (maximum is 65536 characters)`.
+  max_pr_desc_char_length=65000
+  version=$(jq -r '.version' package.json)
+  echo "version=$version" >> $GITHUB_OUTPUT
+  read -d '' pr_header <<EOF
+This PR is a preview of the changes that will be included in the next release. Please do not merge this PR.
+
+# Chainlink Core Release - v${version}
+---
+EOF
+  if [[ ${#changelog_content} -gt $max_pr_desc_char_length ]]; then
+    read -d '' pr_body <<EOF
+${pr_header}
+
+The changelog content is too long for the PR description. Please view the full changelog in the [CHANGELOG.md](https://github.com/smartcontractkit/chainlink/blob/changesets/release-preview/CHANGELOG.md)
+EOF
+  else
+    read -d '' pr_body <<EOF
+${pr_header}
+
+${changelog_content}
+EOF
+  fi
+  echo "pr_body=$pr_body" >> $GITHUB_OUTPUT
+}
+
 set_new_changelog_content() {
-  append_changelog_content
   read -d '' new_changelog <<EOF
 ${changelog_content}
 ${current_changelog}
@@ -130,5 +157,7 @@ while IFS= read -r line; do
 done < CHANGELOG.md
 
 match_tags
+append_changelog_content
+set_pr_body
 set_new_changelog_content
 cleanup