fix: simplify branch 'breaking' logic and add missing file

Author: rpocklin

.github/workflows/api-diff.yml

@@ -0,0 +1,45 @@
+name: OpenAPI Spec Diff Check
+
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+      - main
+
+# Cancel in-progress runs for the same PR/branch
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  test-branch-logic:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v4
+    
+    - name: Run branch logic unit tests
+      run: ./scripts/api-diff/api-diff.test.sh
+  
+  api-diff:
+    runs-on: ubuntu-latest
+    needs: test-branch-logic
+    permissions:
+      contents: read
+      pull-requests: write
+    
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v4
+      with:
+        fetch-depth: 0
+    
+    - name: Pull oasdiff Docker image
+      run: docker pull tufin/oasdiff:latest
+    
+    - name: Make script executable
+      run: chmod +x scripts/api-diff/api-diff.sh
+    
+    - name: Run API diff check
+      run: ./scripts/api-diff/api-diff.sh

scripts/api-diff/api-diff.sh

@@ -26,6 +26,18 @@ for arg in "$@"; do
     fi
 done
 
+# If --fail-on-breaking not explicitly set, determine based on branch name
+if [ "$FAIL_ON_BREAKING" = false ]; then
+    CURRENT_BRANCH=$(git branch --show-current 2>/dev/null || echo "")
+    if [[ "$CURRENT_BRANCH" == *breaking* ]]; then
+        echo "Branch '$CURRENT_BRANCH' contains 'breaking', allowing breaking changes"
+        FAIL_ON_BREAKING=false
+    else
+        echo "Branch '$CURRENT_BRANCH' does not contain 'breaking', failing on breaking changes"
+        FAIL_ON_BREAKING=true
+    fi
+fi
+
 echo "Starting API diff check..."
 
 # Ensure we're in the repo root