CI: make target branch fall back to selected branch

.github/workflows/docker-build.yml

@@ -4,9 +4,10 @@ on:
   workflow_dispatch:
     inputs:
       branch:
-        description: "Branch to build (e.g. my-feature-branch)"
+        description: "Branch to build (defaults to selected branch)"
         type: string
-        required: true
+        required: false
+        default: ""
       containers:
         description: "Comma-separated container names to build, or 'all' for all containers"
         type: string
@@ -26,27 +27,33 @@ permissions:
   id-token: write
 
 jobs:
-  detect-changes:
+  setup:
     runs-on: ubuntu-latest
-    if: inputs.branch != 'main'
     outputs:
+      branch: ${{ steps.resolve.outputs.branch }}
       containers: ${{ steps.detect.outputs.containers }}
       downstream_containers: ${{ steps.detect.outputs.downstream_containers }}
       image_tag: ${{ steps.detect.outputs.image_tag }}
     steps:
+      - name: Resolve branch
+        id: resolve
+        run: |
+          BRANCH="${{ inputs.branch || github.ref_name }}"
+          echo "branch=$BRANCH" >> $GITHUB_OUTPUT
+
       - name: Checkout repository
         uses: actions/checkout@v6
         with:
-          ref: ${{ inputs.branch }}
+          ref: ${{ steps.resolve.outputs.branch }}
 
-      - name: Detect containers to build
+      - name: Resolve containers to build
         id: detect
         run: |
           # Compute image tag from branch name unless an explicit tag was provided
           if [[ -n "${{ inputs.tag }}" ]]; then
             IMAGE_TAG="${{ inputs.tag }}"
           else
-            IMAGE_TAG="dev-$(echo "${{ inputs.branch }}" | tr '[:upper:]' '[:lower:]' | sed 's/[^a-z0-9._-]/-/g')"
+            IMAGE_TAG="dev-$(echo "${{ steps.resolve.outputs.branch }}" | tr '[:upper:]' '[:lower:]' | sed 's/[^a-z0-9._-]/-/g')"
           fi
           echo "image_tag=$IMAGE_TAG" >> $GITHUB_OUTPUT
 
@@ -125,22 +132,22 @@ jobs:
           fi
 
   build:
-    needs: [ detect-changes ]
-    if: needs.detect-changes.outputs.containers != '[]'
+    needs: [ setup ]
+    if: needs.setup.outputs.containers != '[]'
     runs-on: ubuntu-24.04-arm
     env:
       PYTHON_VERSION: "3.13"
       TASKFILE_VERSION: "3.45.4"
     strategy:
       fail-fast: false
       matrix:
-        container: ${{ fromJson(needs.detect-changes.outputs.containers) }}
+        container: ${{ fromJson(needs.setup.outputs.containers) }}
 
     steps:
       - name: Checkout repository
         uses: actions/checkout@v6
         with:
-          ref: ${{ inputs.branch }}
+          ref: ${{ needs.setup.outputs.branch }}
 
       - name: Set up Python
         if: matrix.container == 'python-apps-base'
@@ -173,8 +180,8 @@ jobs:
         uses: docker/metadata-action@v4
         with:
           tags: |
-            type=raw,value=${{ needs.detect-changes.outputs.image_tag }}
-            type=raw,value=${{ needs.detect-changes.outputs.image_tag }}-${{ github.run_number }}
+            type=raw,value=${{ needs.setup.outputs.image_tag }}
+            type=raw,value=${{ needs.setup.outputs.image_tag }}-${{ github.run_number }}
           images: ghcr.io/${{ github.repository_owner }}/app-bricks/${{ matrix.container }}
 
       - name: Build and push Docker image
@@ -192,22 +199,22 @@ jobs:
             REGISTRY=${{ env.DEV_REGISTRY_PATH }}
 
   build-downstream:
-    needs: [ detect-changes, build ]
-    if: needs.detect-changes.outputs.downstream_containers != '[]'
+    needs: [ setup, build ]
+    if: needs.setup.outputs.downstream_containers != '[]'
     runs-on: ubuntu-24.04-arm
     env:
       PYTHON_VERSION: "3.13"
       TASKFILE_VERSION: "3.45.4"
     strategy:
       fail-fast: false
       matrix:
-        container: ${{ fromJson(needs.detect-changes.outputs.downstream_containers) }}
+        container: ${{ fromJson(needs.setup.outputs.downstream_containers) }}
 
     steps:
       - name: Checkout repository
         uses: actions/checkout@v6
         with:
-          ref: ${{ inputs.branch }}
+          ref: ${{ needs.setup.outputs.branch }}
 
       - name: Set up Python
         if: matrix.container == 'python-apps-base'
@@ -240,8 +247,8 @@ jobs:
         uses: docker/metadata-action@v4
         with:
           tags: |
-            type=raw,value=${{ needs.detect-changes.outputs.image_tag }}
-            type=raw,value=${{ needs.detect-changes.outputs.image_tag }}-${{ github.run_number }}
+            type=raw,value=${{ needs.setup.outputs.image_tag }}
+            type=raw,value=${{ needs.setup.outputs.image_tag }}-${{ github.run_number }}
           images: ghcr.io/${{ github.repository_owner }}/app-bricks/${{ matrix.container }}
 
       - name: Build and push Docker image
@@ -257,4 +264,4 @@ jobs:
           provenance: false
           build-args: |
             REGISTRY=${{ env.DEV_REGISTRY_PATH }}
-            BASE_IMAGE_VERSION=${{ needs.detect-changes.outputs.image_tag }}
+            BASE_IMAGE_VERSION=${{ needs.setup.outputs.image_tag }}