Implement draft-release workflow

.github/workflows/draft-release.yml

@@ -1,6 +1,7 @@
-# Placeholder draft-release workflow
+# Drafts new mailtrap-python release: bumps the version, regenerates the changelog from
+# merged PRs, and opens a release PR against main.
 #
-name: Draft python Release
+name: Draft Python Release
 on:
   workflow_dispatch:
     inputs:
@@ -14,14 +15,72 @@ on:
           - major
         default: patch
 
+concurrency:
+  group: ${{ github.workflow }}
+  cancel-in-progress: false
+
+permissions:
+  contents: write
+  pull-requests: write
+
 jobs:
   draft-release:
-    name: Draft python Release (placeholder)
+    name: Draft mailtrap-python Release
     runs-on: ubuntu-latest
     steps:
-      - name: Echo inputs
-        env:
-          BUMP_TYPE: ${{ inputs.bump_type }}
-        run: |
-          echo "Placeholder draft-release workflow"
-          echo "bump_type=$BUMP_TYPE"
+      - uses: actions/checkout@v4
+        with:
+          ref: main
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v6
+
+      - name: Read current version
+        id: read
+        run: echo "version=$(uv version --short)" >> "$GITHUB_OUTPUT"
+
+      - name: Compute next version
+        id: bump
+        uses: railsware/github-actions/compute-next-semver@master
+        with:
+          current: ${{ steps.read.outputs.version }}
+          bump-type: ${{ inputs.bump_type }}
+
+      - name: Abort if tag already exists
+        uses: railsware/github-actions/abort-if-tag-exists@master
+        with:
+          tag: ${{ steps.bump.outputs.tag }}
+
+      - name: Generate release notes
+        id: notes
+        uses: railsware/github-actions/generate-release-notes@master
+        with:
+          tag: ${{ steps.bump.outputs.tag }}
+
+      - name: Update version in pyproject.toml
+        if: steps.notes.outputs.release_notes != ''
+        run: uv version --no-sync "${{ steps.bump.outputs.next }}"
+
+      - name: Prepend new section to CHANGELOG.md
+        if: steps.notes.outputs.release_notes != ''
+        uses: railsware/github-actions/prepend-changelog@master
+        with:
+          version: ${{ steps.bump.outputs.next }}
+          release-notes: ${{ steps.notes.outputs.release_notes }}
+
+      - name: Commit, push, open PR
+        if: steps.notes.outputs.release_notes != ''
+        uses: railsware/github-actions/open-sdk-release-pr@master
+        with:
+          tag: ${{ steps.bump.outputs.tag }}
+          current: ${{ steps.read.outputs.version }}
+          next: ${{ steps.bump.outputs.next }}
+          bump-type: ${{ inputs.bump_type }}
+          release-notes: ${{ steps.notes.outputs.release_notes }}
+
+      - name: Create draft GitHub release
+        if: steps.notes.outputs.release_notes != ''
+        uses: railsware/github-actions/create-draft-github-release@master
+        with:
+          tag: ${{ steps.bump.outputs.tag }}
+          release-notes: ${{ steps.notes.outputs.release_notes }}