ci: refine image detection logic in build workflow

Updated the image detection step in the `.gitea/workflows/build-images.yml` workflow to better handle manual inputs and automatic change detection.

Changes:
- Reorganized the logic to handle manual inputs first; if a manual input is present, it validates the image, sets the output matrix immediately, and exits, bypassing git diff checks.
- Added explicit error handling and output setting for invalid or empty manual inputs to prevent workflow failure confusion.
- Grouped the Git diff detection logic into a distinct block that runs only if no manual input is provided.
- Added a debug echo statement to the build job to verify the current matrix image being built.

.gitea/workflows/build-images.yml

@@ -37,25 +37,36 @@ jobs:
       - name: Detect changed images
         id: changes
         run: |
-          # Prepare output file for valid images
+          # 1. Handle Manual Input
-          > valid_images.txt
-
           if [ -n "${{ inputs.image }}" ]; then
-            # Manual trigger with input
+            # Clean input
             IMAGE=$(echo "${{ inputs.image }}" | xargs)
             if [ -n "$IMAGE" ]; then
               if [ -d "images/$IMAGE" ] && [ -f "images/$IMAGE/Dockerfile" ]; then
-                 echo "$IMAGE" >> valid_images.txt
+                 echo "Manual image detected: $IMAGE"
+                 echo "matrix=[\"$IMAGE\"]" >> $GITHUB_OUTPUT
+                 echo "has_changes=true" >> $GITHUB_OUTPUT
+                 exit 0
               else
-                 echo "Warning: Image '$IMAGE' not found or missing Dockerfile at images/$IMAGE/Dockerfile"
+                 echo "Error: Image '$IMAGE' not found or missing Dockerfile at images/$IMAGE/Dockerfile"
-              fi
+                 echo "has_changes=false" >> $GITHUB_OUTPUT
+                 echo "matrix=[]" >> $GITHUB_OUTPUT
+                 exit 0
               fi
             else
-            # Automatic detection via git diff
+               echo "Input image name was empty."
+               echo "has_changes=false" >> $GITHUB_OUTPUT
+               echo "matrix=[]" >> $GITHUB_OUTPUT
+               exit 0
+            fi
+          fi
+
+          # 2. Handle Automatic Detection (Git Diff)
+          > valid_images.txt
+          
           CHANGED_FILES=$(git diff --name-only HEAD~1 HEAD -- images/ 2>/dev/null || true)
           
           # Extract potential image directories (first level subdirs in images/)
-            # cut -d'/' -f2 takes the second component: images/COMPONENT/...
           CANDIDATES=$(echo "$CHANGED_FILES" | cut -d'/' -f2 | sort -u | grep -v '^$')
           
           for CANDIDATE in $CANDIDATES; do
@@ -64,7 +75,6 @@ jobs:
               echo "$CANDIDATE" >> valid_images.txt
             fi
           done
-          fi
           
           if [ ! -s valid_images.txt ]; then
              echo "No valid images detected."
@@ -114,6 +124,8 @@ jobs:
           IMAGE_NAME: ${{ env.REGISTRY }}/damien/${{ matrix.image }}
           IMAGE_PATH: images/${{ matrix.image }}
         run: |
+          echo "Debug: Matrix Image is '${{ matrix.image }}'"
+          
           if [ -z "${{ matrix.image }}" ]; then
             echo "Skipping empty image name"
             exit 0