chore: add breaking change detector

.github/workflows/breaking-change-detector.yml

@@ -0,0 +1,102 @@
+name: Breaking Change Detector
+
+on:
+  pull_request:
+    branches:
+      - main
+    paths:
+      - 'src/**'
+
+jobs:
+  check-api:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0  # Required for accessing the main branch history
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.10'
+
+      - name: Install the latest version of uv
+        uses: astral-sh/setup-uv@v5
+
+      - name: Install dependencies
+        # Syncing installs the package and its dependencies (populating google.* namespace)
+        # Installing 'griffe' ensures the tool is available in the environment
+        run: |
+          uv sync --extra test
+          uv pip install griffe
+
+      - name: Run Breaking Change Detection
+        # Uses 'uv run python' to execute in the environment with all dependencies installed
+        run: |
+          uv run python - <<EOF
+          import sys
+          import griffe
+          from griffe import find_breaking_changes, load, load_git
+
+          def check_return_types(old_obj, new_obj):
+              """Custom check to strictly compare return type annotations."""
+              errors = []
+              # Check Runner.run specifically, or extend to check all methods
+              try:
+                  old_run = old_obj.members["Runner"].members["run"]
+                  new_run = new_obj.members["Runner"].members["run"]
+
+                  # Convert to string and strip to compare the annotation text
+                  old_ret = str(old_run.returns).strip()
+                  new_ret = str(new_run.returns).strip()
+
+                  if old_ret != new_ret:
+                      errors.append(
+                          f"Breaking Change in {new_run.path}: Return type changed from '{old_ret}' to '{new_ret}'"
+                      )
+              except KeyError:
+                  pass # Member missing (will be caught by standard checks)
+              except AttributeError:
+                  pass # Member might not be a function
+              return errors
+
+          try:
+              print("Loading new API (from local source)...")
+              # allow_inspection=False forces static analysis, preventing sys.modules caching issues
+              new_api = load("google.adk", search_paths=["src"], allow_inspection=False)
+
+              print("Loading baseline API (from main branch)...")
+              old_api = load_git("google.adk", ref="main", search_paths=["src"], allow_inspection=False)
+
+              print("Running detection...")
+
+              # 1. Standard Griffe Checks (Removals, Parameter changes)
+              breakages = list(find_breaking_changes(old_api, new_api))
+
+              # 2. Custom Return Type Checks (Workaround for Griffe limitation)
+              custom_errors = check_return_types(old_api, new_api)
+
+              found_issues = False
+
+              if breakages:
+                  found_issues = True
+                  print(f"::error::Found {len(breakages)} standard breaking changes!")
+                  for breakage in breakages:
+                      print(breakage.explain())
+
+              if custom_errors:
+                  found_issues = True
+                  print(f"::error::Found {len(custom_errors)} return type mismatches!")
+                  for error in custom_errors:
+                      print(f"- {error}")
+
+              if found_issues:
+                  sys.exit(1)
+
+              print("Success: No breaking changes detected.")
+
+          except Exception as e:
+              print(f"::error::Breaking change detection failed: {e}")
+              sys.exit(1)
+          EOF

src/google/adk/runners.py

@@ -353,7 +353,7 @@ def run(
       session_id: str,
       new_message: types.Content,
       run_config: Optional[RunConfig] = None,
-  ) -> Generator[Event, None, None]:
+  ) -> Generator[dict, None, None]:
     """Runs the agent.
 
     NOTE: