fix: avoid unsafe yaml load in conformance tests

AGENTS.md

@@ -54,6 +54,23 @@ again on every replay. This implies four rules:
 See [Determinism and Replay](https://docs.aws.amazon.com/durable-execution/patterns/best-practices/determinism/)
 for worked examples.
 
+## Security-sensitive parsing
+
+- Do not use `yaml.load()` or `yaml.load_all()`, including with `Loader=`
+  arguments or suppression comments. CodeQL and security scanners flag the
+  unsafe call form even when the loader subclasses `yaml.SafeLoader`.
+- Use `yaml.safe_load()` or `yaml.safe_load_all()` for plain YAML.
+- For CloudFormation or SAM templates with short-form tags such as `!Ref`,
+  `!Sub`, `!GetAtt`, or `!If`, use a `yaml.SafeLoader` subclass with explicit
+  tag constructors so the tags are preserved.
+- For custom safe loaders, instantiate the loader directly, call
+  `get_single_data()` or the equivalent multi-document API, and call
+  `dispose()` in a `finally` block. This matches what `yaml.safe_load()` does
+  internally while preserving custom tag support.
+- Before finishing YAML-related changes, check Python code for unsafe call
+  forms:
+  `rg -n --glob '*.py' "yaml\\.load\\b|yaml\\.load_all\\b|from yaml import load\\b|from yaml import load_all\\b" .`
+
 ## Testing Requirements
 
 All changes MUST include related tests. At minimum, include **unit tests**. Include **e2e integration tests** (in the `tests/e2e/` directory) when the change affects cross-component behavior, public API surfaces, or end-to-end workflows. For isolated bug fixes where a unit test alone sufficiently covers the fix, integration tests are not required.

packages/aws-durable-execution-sdk-python-conformance-tests-otel/tests/test_otel_examples.py

@@ -194,9 +194,22 @@ def _construct_cfn_tag(loader: CfnLoader, _suffix: str, node: yaml.Node) -> CfnT
 CfnLoader.add_multi_constructor("!", _construct_cfn_tag)
 
 
+def _safe_load_cfn(stream: object) -> Any:
+    """Safely load a CloudFormation template with short-form tags.
+
+    Equivalent to yaml.safe_load (CfnLoader extends yaml.SafeLoader) while
+    additionally preserving CloudFormation short-form tags.
+    """
+    loader = CfnLoader(stream)
+    try:
+        return loader.get_single_data()
+    finally:
+        loader.dispose()
+
+
 def load_template(path: Path) -> dict[str, Any]:
     with path.open(encoding="utf-8") as stream:
-        template: dict[str, Any] = yaml.load(stream, Loader=CfnLoader)
+        template: dict[str, Any] = _safe_load_cfn(stream)
     return template