From 1bb3bb8d2e1cc0003e6ace50abdfae28d3c04633 Mon Sep 17 00:00:00 2001
From: j-zhangyiyuan <j-zhangyiyuan@microsoft.com>
Date: Mon, 3 Aug 2026 10:30:35 +0800
Subject: [PATCH 1/2] fix(python): serialize Pydantic models with mode='json'
 in tool results

model_dump() defaults to mode='python', which leaves datetime, UUID,
Decimal, Enum and set as native Python objects. json.dumps then fails
on these, and the error is swallowed as a generic tool failure.

Use model_dump(mode='json') so Pydantic converts all fields to
JSON-safe types before serialization.

Closes #2203
---
 python/copilot/tools.py |  2 +-
 python/test_tools.py    | 30 ++++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/python/copilot/tools.py b/python/copilot/tools.py
index 762b79c45b..de81fe7fd8 100644
--- a/python/copilot/tools.py
+++ b/python/copilot/tools.py
@@ -351,7 +351,7 @@ def _normalize_result(result: Any) -> ToolResult:
     # Everything else gets JSON-serialized (with Pydantic model support)
     def default(obj: Any) -> Any:
         if isinstance(obj, BaseModel):
-            return obj.model_dump()
+            return obj.model_dump(mode="json")
         raise TypeError(f"Object of type {type(obj).__name__} is not JSON serializable")
 
     try:
diff --git a/python/test_tools.py b/python/test_tools.py
index 646f17c03a..f751082679 100644
--- a/python/test_tools.py
+++ b/python/test_tools.py
@@ -389,6 +389,36 @@ class Item(BaseModel):
         assert parsed == [{"name": "a", "value": 1}, {"name": "b", "value": 2}]
         assert result.result_type == "success"
 
+    def test_pydantic_model_with_non_primitive_fields_is_serialized(self):
+        from datetime import datetime, date
+        from decimal import Decimal
+        from enum import Enum
+        from uuid import UUID
+
+        class Status(Enum):
+            ACTIVE = "active"
+
+        class Record(BaseModel):
+            id: UUID
+            created: datetime
+            day: date
+            score: Decimal
+            status: Status
+
+        record = Record(
+            id=UUID("12345678-1234-5678-1234-567812345678"),
+            created=datetime(2026, 1, 15, 10, 30, 0),
+            day=date(2026, 1, 15),
+            score=Decimal("99.5"),
+            status=Status.ACTIVE,
+        )
+        result = _normalize_result(record)
+        parsed = json.loads(result.text_result_for_llm)
+        assert parsed["id"] == "12345678-1234-5678-1234-567812345678"
+        assert parsed["status"] == "active"
+        assert parsed["score"] == "99.5"
+        assert result.result_type == "success"
+
     def test_raises_for_unserializable_value(self):
         # Functions cannot be JSON serialized
         with pytest.raises(TypeError, match="Failed to serialize"):

From 6488526fa25518db4a4c9c7a66097a0c2d6b7ed2 Mon Sep 17 00:00:00 2001
From: Steve Sanderson <SteveSandersonMS@users.noreply.github.com>
Date: Mon, 3 Aug 2026 13:01:34 +0000
Subject: [PATCH 2/2] test(python): strengthen Pydantic result coverage

Assert the JSON representation of date and datetime fields, cover set serialization, and fix import ordering for Ruff.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 python/test_tools.py | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/python/test_tools.py b/python/test_tools.py
index f751082679..97de41df42 100644
--- a/python/test_tools.py
+++ b/python/test_tools.py
@@ -390,7 +390,7 @@ class Item(BaseModel):
         assert result.result_type == "success"
 
     def test_pydantic_model_with_non_primitive_fields_is_serialized(self):
-        from datetime import datetime, date
+        from datetime import date, datetime
         from decimal import Decimal
         from enum import Enum
         from uuid import UUID
@@ -404,6 +404,7 @@ class Record(BaseModel):
             day: date
             score: Decimal
             status: Status
+            tags: set[str]
 
         record = Record(
             id=UUID("12345678-1234-5678-1234-567812345678"),
@@ -411,12 +412,19 @@ class Record(BaseModel):
             day=date(2026, 1, 15),
             score=Decimal("99.5"),
             status=Status.ACTIVE,
+            tags={"python", "sdk"},
         )
         result = _normalize_result(record)
         parsed = json.loads(result.text_result_for_llm)
-        assert parsed["id"] == "12345678-1234-5678-1234-567812345678"
-        assert parsed["status"] == "active"
-        assert parsed["score"] == "99.5"
+        assert parsed == {
+            "id": "12345678-1234-5678-1234-567812345678",
+            "created": "2026-01-15T10:30:00",
+            "day": "2026-01-15",
+            "score": "99.5",
+            "status": "active",
+            "tags": parsed["tags"],
+        }
+        assert set(parsed["tags"]) == {"python", "sdk"}
         assert result.result_type == "success"
 
     def test_raises_for_unserializable_value(self):