fix(streaming): log warning when tool input JSON is malformed

Malformed tool input JSON was silently replaced with an empty dict,
with no logging. The tool then ran with empty arguments and the model
had no indication its JSON was invalid.

Added a logger.warning() call before the fallback so operators can
detect and diagnose this in production.

Fixes #2051

Author: Ratansairohith

src/strands/event_loop/streaming.py

@@ -279,6 +279,11 @@ def handle_content_block_stop(state: dict[str, Any]) -> dict[str, Any]:
         try:
             current_tool_use["input"] = json.loads(current_tool_use["input"])
         except ValueError:
+            logger.warning(
+                "Failed to parse tool input JSON for '%s': %s",
+                current_tool_use.get("name", "unknown"),
+                current_tool_use["input"][:200] if isinstance(current_tool_use.get("input"), str) else "",
+            )
             current_tool_use["input"] = {}
 
         tool_use_id = current_tool_use["toolUseId"]

tests/strands/event_loop/test_streaming.py

@@ -366,6 +366,25 @@ def test_handle_content_block_delta(event: ContentBlockDeltaEvent, event_type, s
                 "redactedContent": b"",
             },
         ),
+        # Tool Use - Malformed input JSON
+        (
+            {
+                "content": [],
+                "current_tool_use": {"toolUseId": "123", "name": "test", "input": "{invalid json}"},
+                "text": "",
+                "reasoningText": "",
+                "citationsContent": [],
+                "redactedContent": b"",
+            },
+            {
+                "content": [{"toolUse": {"toolUseId": "123", "name": "test", "input": {}}}],
+                "current_tool_use": {},
+                "text": "",
+                "reasoningText": "",
+                "citationsContent": [],
+                "redactedContent": b"",
+            },
+        ),
         # Text
         (
             {