ci: fix release workflow changelog extraction

The shell changelog-render/update scripts were removed when prepare-release
moved to a Go tool, but release.yml still called them. Extract the tagged
section from CHANGELOG.md instead, and drop the obsolete prepare-release
workflow in favor of the local go tool.

Signed-off-by: crozzy <joseph.crosland@gmail.com>

Author: crozzy

.github/workflows/prepare-release.yml

@@ -20,11 +20,19 @@ jobs:
         uses: actions/checkout@v7
         with:
           fetch-depth: 0
-          persist-credentials: true # Needed to fetch the changelog ref.
       - name: Changelog
+        # The CHANGELOG.md section for this tag is the source of truth; it was
+        # written by prepare-release before the tag was cut.
         run: |
-          git fetch origin refs/notes/changelog:refs/notes/changelog
-          .github/scripts/changelog-render "${VERSION}" > "${GITHUB_WORKSPACE}/changelog"
+          awk -v ver="${VERSION}" '
+            index($0, "<a name=\"" ver "\"></a>") == 1 { found = 1 }
+            found && /^<a name="/ && index($0, ver) == 0 { exit }
+            found { print }
+          ' CHANGELOG.md > "${GITHUB_WORKSPACE}/changelog"
+          if ! grep -q . "${GITHUB_WORKSPACE}/changelog"; then
+            echo "::error::no CHANGELOG.md section found for ${VERSION}"
+            exit 1
+          fi
       - name: Create Release
         uses: actions/create-release@latest
         env:

.github/workflows/release.yml

@@ -22,12 +22,8 @@ The primary helper script is `changelog-edit`. It allows a user to sync down
 notes, edit an entry, or both. See the output of the `h` flag for more
 information.
 
-The other script of interest is `changelog-render`, which can be used to render
-out the changelog on demand, assuming the changelog notes have been pulled
-locally.
-
-The `changelog-update` script uses `changelog-render` to add to the
-`CHANGELOG.md` file in the repository root.
+To turn notes into a `CHANGELOG.md` section and open a release PR, use
+`go tool prepare-release` (see [Releases](./releases.md)).
 
 ### Formatting