feat: auto-release images from conventional commits on main

On each push to main, derive the next semantic version from the
conventional-commit messages since the last v* tag (feat -> minor,
fix/perf -> patch, \! or BREAKING CHANGE -> major) and, when a release is
warranted, build and publish the image tagged X.Y.Z, X.Y, X and latest,
then record an annotated vX.Y.Z tag for the next computation. Non-release
pushes publish a sha-<short> image only.

Configure Renovate to commit updates as fix(deps): so each merged Renovate
PR registers as a patch change and is released and tagged automatically.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/build-and-publish.yml

@@ -3,29 +3,99 @@ name: Build and publish container
 on:
   push:
     branches: [main]
-    tags: ["v*"]
   pull_request:
     branches: [main]
 
+defaults:
+  run:
+    shell: bash
+
 jobs:
   build:
     runs-on: ubuntu-latest
     permissions:
-      contents: read
+      contents: write
       packages: write
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+        with:
+          # Full history and tags are required to derive the next version
+          # from the conventional-commit messages since the last release.
+          fetch-depth: 0
 
       - name: Determine registry host
         run: echo "REGISTRY=${GITHUB_SERVER_URL#*://}" >> "$GITHUB_ENV"
 
+      # Derive the release version from conventional commits since the last
+      # v* tag: feat -> minor, fix/perf -> patch, ! or BREAKING CHANGE -> major.
+      # Anything else (chore, ci, docs, build) produces no release; those builds
+      # are published under a sha-<short> tag only.
+      - name: Compute version and image tags
+        id: version
+        run: |
+          set -euo pipefail
+          image="${REGISTRY}/${GITHUB_REPOSITORY,,}"
+
+          last_tag="$(git tag --list 'v*' --sort=-v:refname | head -n1 || true)"
+          if [ -n "$last_tag" ]; then
+            range="${last_tag}..HEAD"
+            base="${last_tag#v}"
+          else
+            range=""
+            base="0.0.0"
+          fi
+
+          subjects="$(git log ${range} --format='%s')"
+          bodies="$(git log ${range} --format='%B')"
+
+          bump="none"
+          if printf '%s\n' "$bodies" | grep -qiE 'BREAKING[ -]CHANGE' \
+             || printf '%s\n' "$subjects" | grep -qE '^[a-z]+([(][^)]*[)])?!:'; then
+            bump="major"
+          elif printf '%s\n' "$subjects" | grep -qE '^feat([(][^)]*[)])?:'; then
+            bump="minor"
+          elif printf '%s\n' "$subjects" | grep -qE '^(fix|perf)([(][^)]*[)])?:'; then
+            bump="patch"
+          fi
+
+          major="${base%%.*}"
+          rest="${base#*.}"
+          minor="${rest%%.*}"
+          patch="${rest##*.}"
+
+          release="false"
+          if [ "${GITHUB_EVENT_NAME}" = "push" ] && [ "$bump" != "none" ]; then
+            release="true"
+            case "$bump" in
+              major) major=$((major + 1)); minor=0; patch=0 ;;
+              minor) minor=$((minor + 1)); patch=0 ;;
+              patch) patch=$((patch + 1)) ;;
+            esac
+            version="${major}.${minor}.${patch}"
+            {
+              echo "tags<<__EOT__"
+              echo "${image}:${version}"
+              echo "${image}:${major}.${minor}"
+              echo "${image}:${major}"
+              echo "${image}:latest"
+              echo "__EOT__"
+            } >> "$GITHUB_OUTPUT"
+            echo "version=${version}" >> "$GITHUB_OUTPUT"
+          else
+            short="$(git rev-parse --short HEAD)"
+            {
+              echo "tags<<__EOT__"
+              echo "${image}:sha-${short}"
+              echo "__EOT__"
+            } >> "$GITHUB_OUTPUT"
+          fi
+          echo "release=${release}" >> "$GITHUB_OUTPUT"
+          echo "Computed bump=${bump}, release=${release}, base=${base}"
+
       - name: Set up Buildx
         uses: docker/setup-buildx-action@v3
 
-      # Uses a Personal Access Token with package read/write scope, stored as
-      # the PACKAGES_TOKEN secret. The auto-provided GITEA_TOKEN does not carry
-      # container-registry write permission on most Gitea instances.
       - name: Log in to the Gitea container registry
         if: github.event_name != 'pull_request'
         uses: docker/login-action@v3
@@ -34,28 +104,25 @@ jobs:
           username: ${{ github.repository_owner }}
           password: ${{ secrets.PACKAGES_TOKEN }}
 
-      - name: Extract image metadata
-        id: meta
-        uses: docker/metadata-action@v5
-        with:
-          images: ${{ env.REGISTRY }}/${{ github.repository }}
-          # Semantic version tags are produced from pushed v* git tags.
-          # `latest` follows the newest non-prerelease release via latest=auto.
-          # Branch and SHA tags are kept for traceability of non-release builds.
-          tags: |
-            type=semver,pattern={{version}}
-            type=semver,pattern={{major}}.{{minor}}
-            type=semver,pattern={{major}}
-            type=ref,event=branch
-            type=ref,event=pr
-            type=sha
-          flavor: |
-            latest=auto
-
       - name: Build and push
         uses: docker/build-push-action@v6
         with:
           context: .
           push: ${{ github.event_name != 'pull_request' }}
-          tags: ${{ steps.meta.outputs.tags }}
-          labels: ${{ steps.meta.outputs.labels }}
+          tags: ${{ steps.version.outputs.tags }}
+          labels: |
+            org.opencontainers.image.source=${{ github.server_url }}/${{ github.repository }}
+            org.opencontainers.image.revision=${{ github.sha }}
+
+      # Record the release as an annotated git tag so the next run computes the
+      # following version from it. This push does not re-trigger the workflow,
+      # which only listens on the main branch and pull requests.
+      - name: Tag the release
+        if: steps.version.outputs.release == 'true'
+        run: |
+          set -euo pipefail
+          v="v${{ steps.version.outputs.version }}"
+          git config user.name "${{ github.actor }}"
+          git config user.email "${{ github.actor }}@users.noreply.${REGISTRY}"
+          git tag -a "$v" -m "$v"
+          git push origin "$v"