From b0f8350c7fe3321f215ed591841dec4b146703cb Mon Sep 17 00:00:00 2001
From: Henry Su <henrysu4707@gmail.com>
Date: Thu, 20 Aug 2026 12:49:18 -0500
Subject: [PATCH] fix(approvals): fail closed on empty tool arguments

Missing or blank argument strings were coerced to {} before callable
needs_approval ran, so content gates could skip interruption.
---
 src/agents/util/_approvals.py      | 4 +++-
 tests/realtime/test_session.py     | 1 +
 tests/test_hitl_error_scenarios.py | 1 +
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/agents/util/_approvals.py b/src/agents/util/_approvals.py
index 0aa86d9965..8992f5ada2 100644
--- a/src/agents/util/_approvals.py
+++ b/src/agents/util/_approvals.py
@@ -17,9 +17,11 @@ def _reject_nonstandard_json_constant(value: str) -> NoReturn:
 
 def parse_function_tool_arguments(arguments: str | None) -> dict[str, Any] | None:
     """Return parsed object arguments, or None when an approval policy cannot inspect them."""
+    if arguments is None or not arguments.strip():
+        return None
     try:
         parsed = json.loads(
-            arguments or "{}",
+            arguments,
             parse_constant=_reject_nonstandard_json_constant,
         )
     except ValueError:
diff --git a/tests/realtime/test_session.py b/tests/realtime/test_session.py
index 9d8f813bae..ab0ac5ebfc 100644
--- a/tests/realtime/test_session.py
+++ b/tests/realtime/test_session.py
@@ -3125,6 +3125,7 @@ async def test_function_tool_needs_approval_emits_event(
     @pytest.mark.parametrize(
         "arguments",
         [
+            "",
             '{"subject": "refund"',
             "null",
             "[]",
diff --git a/tests/test_hitl_error_scenarios.py b/tests/test_hitl_error_scenarios.py
index d8518088cf..eb59cb1ce1 100644
--- a/tests/test_hitl_error_scenarios.py
+++ b/tests/test_hitl_error_scenarios.py
@@ -919,6 +919,7 @@ def bad_tool() -> str:
 @pytest.mark.parametrize(
     "arguments",
     [
+        "",
         '{"subject": "refund"',
         "null",
         "[]",