From 00a7de0171e6994b627d37b6d95fe5252d02fab6 Mon Sep 17 00:00:00 2001
From: Xubin Ren <52506698+Re-bin@users.noreply.github.com>
Date: Fri, 26 Jun 2026 11:10:03 +0800
Subject: [PATCH] fix: stringify Anthropic typeless blocks as JSON

---
 nanobot/providers/anthropic_provider.py       | 15 +++++++++++++--
 tests/providers/test_anthropic_tool_result.py | 13 +++++++++++--
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/nanobot/providers/anthropic_provider.py b/nanobot/providers/anthropic_provider.py
index c52600f6..aa6abc0b 100644
--- a/nanobot/providers/anthropic_provider.py
+++ b/nanobot/providers/anthropic_provider.py
@@ -4,6 +4,7 @@ from __future__ import annotations
 
 import asyncio
 import hashlib
+import json
 import re
 import secrets
 import string
@@ -280,7 +281,10 @@ class AnthropicProvider(LLMProvider):
                         # Anthropic requires every content block to declare a "type".
                         # A tool that returned a bare dict lands here; coerce it to
                         # a text block instead of emitting one that the API rejects.
-                        blocks.append({"type": "text", "text": str(item)})
+                        blocks.append({
+                            "type": "text",
+                            "text": AnthropicProvider._stringify_typeless_block(item),
+                        })
                     else:
                         blocks.append(item)
                 else:
@@ -324,11 +328,18 @@ class AnthropicProvider(LLMProvider):
                 # A tool that returned a bare dict (or a list of dicts) lands
                 # here; coerce it to a text block instead of emitting a block
                 # the API rejects with "content.0.type: Field required".
-                result.append({"type": "text", "text": str(item)})
+                result.append({
+                    "type": "text",
+                    "text": AnthropicProvider._stringify_typeless_block(item),
+                })
                 continue
             result.append(item)
         return result or "(empty)"
 
+    @staticmethod
+    def _stringify_typeless_block(block: dict[str, Any]) -> str:
+        return json.dumps(block, ensure_ascii=False, sort_keys=True, default=str)
+
     @staticmethod
     def _convert_image_block(block: dict[str, Any]) -> dict[str, Any] | None:
         """Convert OpenAI image_url block to Anthropic image block."""
diff --git a/tests/providers/test_anthropic_tool_result.py b/tests/providers/test_anthropic_tool_result.py
index 9cec6769..b08a18fd 100644
--- a/tests/providers/test_anthropic_tool_result.py
+++ b/tests/providers/test_anthropic_tool_result.py
@@ -70,7 +70,7 @@ def test_convert_user_content_coerces_typeless_dict():
         {"foo": "bar"},
         {"type": "text", "text": "ok"},
     ])
-    assert result[0] == {"type": "text", "text": str({"foo": "bar"})}
+    assert result[0] == {"type": "text", "text": '{"foo": "bar"}'}
     assert result[1] == {"type": "text", "text": "ok"}
 
 
@@ -81,7 +81,16 @@ def test_convert_user_content_coerces_mixed_typeless():
         {"key": "val"},
     ])
     assert result[0] == {"type": "text", "text": "42"}
-    assert result[1] == {"type": "text", "text": str({"key": "val"})}
+    assert result[1] == {"type": "text", "text": '{"key": "val"}'}
+
+
+def test_assistant_blocks_coerce_typeless_dict_to_json_text():
+    blocks = AnthropicProvider._assistant_blocks({
+        "role": "assistant",
+        "content": [{"answer": "ok", "count": 2}],
+    })
+
+    assert blocks == [{"type": "text", "text": '{"answer": "ok", "count": 2}'}]
 
 
 def test_convert_assistant_message_repairs_history_tool_arguments():