fix(workflow): treat RetryConfig(max_attempts=0) as no retries

RetryConfig.max_attempts documents "If 0 or 1, it means no retries. If
not specified, default to 5." and defaults to None. _should_retry_node
resolved the default with `retry_config.max_attempts or 5`, which treats
an explicit 0 as falsy and replaces it with 5, so a node configured for
no retries ran up to 5 attempts. Use an explicit None check so 0 and 1
disable retries while the unset (None) case still defaults to 5.

Author: Osamaali313

src/google/adk/workflow/utils/_retry_utils.py

@@ -32,7 +32,9 @@ def _should_retry_node(
     return False
 
   attempt_count = node_state.attempt_count
-  max_attempts = retry_config.max_attempts or 5
+  max_attempts = (
+      retry_config.max_attempts if retry_config.max_attempts is not None else 5
+  )
 
   # attempt_count starts at 1 for the original request.
   # So if attempt_count >= max_attempts, we have reached the limit.

tests/unittests/workflow/utils/test_retry_utils.py

@@ -17,6 +17,7 @@
 from google.adk.workflow._node_state import NodeState
 from google.adk.workflow._retry_config import RetryConfig
 from google.adk.workflow.utils._retry_utils import _get_retry_delay
+from google.adk.workflow.utils._retry_utils import _should_retry_node
 import pytest
 
 
@@ -68,3 +69,36 @@ def test_adds_jitter_when_enabled(self):
 
     assert all(5.0 <= d <= 15.0 for d in delays)
     assert len(set(delays)) > 1
+
+
+class TestShouldRetryNode:
+
+  def test_no_config_never_retries(self):
+    """Without a retry config, a node is never retried."""
+    assert _should_retry_node(RuntimeError(), None, NodeState(attempt_count=1)) is False
+
+  @pytest.mark.parametrize("max_attempts", [0, 1])
+  def test_max_attempts_zero_or_one_disables_retries(self, max_attempts):
+    """max_attempts of 0 or 1 means no retries (per RetryConfig docs).
+
+    A falsy-coalescing default (``max_attempts or 5``) wrongly treated an
+    explicit ``0`` as unset and allowed 5 attempts.
+    """
+    config = RetryConfig(max_attempts=max_attempts)
+
+    assert _should_retry_node(RuntimeError(), config, NodeState(attempt_count=1)) is False
+
+  def test_retries_until_max_attempts(self):
+    """A node is retried while attempt_count is below max_attempts."""
+    config = RetryConfig(max_attempts=3)
+
+    assert _should_retry_node(RuntimeError(), config, NodeState(attempt_count=1)) is True
+    assert _should_retry_node(RuntimeError(), config, NodeState(attempt_count=2)) is True
+    assert _should_retry_node(RuntimeError(), config, NodeState(attempt_count=3)) is False
+
+  def test_unset_max_attempts_defaults_to_five(self):
+    """When max_attempts is unset (None), the default of 5 applies."""
+    config = RetryConfig()
+
+    assert _should_retry_node(RuntimeError(), config, NodeState(attempt_count=4)) is True
+    assert _should_retry_node(RuntimeError(), config, NodeState(attempt_count=5)) is False