feat: Expose branch property on Context

Co-authored-by: Shangjie Chen <deanchen@google.com>
PiperOrigin-RevId: 939138157

Author: DeanChensj

src/google/adk/agents/context.py

@@ -245,6 +245,11 @@ def function_call_id(self, value: str | None) -> None:
     """Sets the function call id of the current tool call."""
     self._function_call_id = value
 
+  @property
+  def branch(self) -> str | None:
+    """The branch path of the current invocation context."""
+    return self._invocation_context.branch
+
   @property
   def isolation_scope(self) -> str | None:
     """Scope tag inherited from parent or set explicitly via override.

tests/unittests/agents/test_context.py

@@ -40,12 +40,21 @@ def mock_invocation_context():
   mock_context.session.id = "test-session-id"
   mock_context.app_name = "test-app"
   mock_context.user_id = "test-user"
+  mock_context.branch = "test-branch"
   mock_context.artifact_service = None
   mock_context.credential_service = None
   mock_context.memory_service = None
   return mock_context
 
 
+def test_context_branch_returns_invocation_branch(mock_invocation_context):
+  """Context.branch returns the branch from the underlying invocation context."""
+  mock_invocation_context.branch = "test-branch"
+  context = Context(invocation_context=mock_invocation_context)
+
+  assert context.branch == "test-branch"
+
+
 @pytest.fixture
 def mock_artifact_service():
   """Create a mock artifact service for testing."""