fix: handle multiple thinking blocks with signatures in chatcmpl converter

Previously only the last signature was preserved when multiple thinking blocks
had signatures. Now all signatures are collected and stored with newline
delimiters, ensuring proper reconstruction of each thinking block.

Author: serialx

src/agents/models/chatcmpl_converter.py

@@ -107,7 +107,7 @@ def message_to_output_items(cls, message: ChatCompletionMessage) -> list[TRespon
             if hasattr(message, "thinking_blocks") and message.thinking_blocks:
                 # Store thinking text in content and signature in encrypted_content
                 reasoning_item.content = []
-                signature = None
+                signatures: list[str] = []
                 for block in message.thinking_blocks:
                     if isinstance(block, dict):
                         thinking_text = block.get("thinking", "")
@@ -116,15 +116,12 @@ def message_to_output_items(cls, message: ChatCompletionMessage) -> list[TRespon
                                 Content(text=thinking_text, type="reasoning_text")
                             )
                         # Store the signature if present
-                        if block.get("signature"):
-                            signature = block.get("signature")
+                        if signature := block.get("signature"):
+                            signatures.append(signature)
 
-                # Store only the last signature in encrypted_content
-                # If there are multiple thinking blocks, this should be a problem.
-                # In practice, there should only be one signature for the entire reasoning step.
-                # Tested with: claude-sonnet-4-20250514
-                if signature:
-                    reasoning_item.encrypted_content = signature
+                # Store the signatures in encrypted_content with newline delimiter
+                if signatures:
+                    reasoning_item.encrypted_content = "\n".join(signatures)
 
             items.append(reasoning_item)
 
@@ -518,7 +515,8 @@ def ensure_assistant_message() -> ChatCompletionAssistantMessageParam:
             elif reasoning_item := cls.maybe_reasoning_message(item):
                 # Reconstruct thinking blocks from content (text) and encrypted_content (signature)
                 content_items = reasoning_item.get("content", [])
-                signature = reasoning_item.get("encrypted_content")
+                encrypted_content = reasoning_item.get("encrypted_content")
+                signatures = encrypted_content.split("\n") if encrypted_content else []
 
                 if content_items and preserve_thinking_blocks:
                     # Reconstruct thinking blocks from content and signature
@@ -532,9 +530,9 @@ def ensure_assistant_message() -> ChatCompletionAssistantMessageParam:
                                 "type": "thinking",
                                 "thinking": content_item.get("text", ""),
                             }
-                            # Add signature if available
-                            if signature:
-                                thinking_block["signature"] = signature
+                            # Add signatures if available
+                            if signatures:
+                                thinking_block["signature"] = signatures.pop(0)
                             pending_thinking_blocks.append(thinking_block)
 
             # 8) If we haven't recognized it => fail or ignore

tests/test_anthropic_thinking_blocks.py

@@ -125,7 +125,12 @@ def test_anthropic_thinking_blocks_with_tool_calls():
                     "Let me use the weather tool to get this information."
                 ),
                 "signature": "TestSignature123",
-            }
+            },
+            {
+                "type": "thinking",
+                "thinking": ("We should use the city Tokyo as the city."),
+                "signature": "TestSignature456",
+            },
         ],
         tool_calls=[
             ChatCompletionMessageToolCall(
@@ -143,7 +148,7 @@ def test_anthropic_thinking_blocks_with_tool_calls():
     reasoning_items = [
         item for item in output_items if hasattr(item, "type") and item.type == "reasoning"
     ]
-    assert len(reasoning_items) == 1, "Should have exactly one reasoning item"
+    assert len(reasoning_items) == 1, "Should have exactly two reasoning items"
 
     reasoning_item = reasoning_items[0]
 
@@ -159,7 +164,9 @@ def test_anthropic_thinking_blocks_with_tool_calls():
     assert hasattr(reasoning_item, "encrypted_content"), (
         "Reasoning item should have encrypted_content"
     )
-    assert reasoning_item.encrypted_content == "TestSignature123", "Signature should be preserved"
+    assert reasoning_item.encrypted_content == "TestSignature123\nTestSignature456", (
+        "Signature should be preserved"
+    )
 
     # Verify tool calls are present
     tool_call_items = [
@@ -210,6 +217,20 @@ def test_anthropic_thinking_blocks_with_tool_calls():
         "Signature should be preserved in thinking block"
     )
 
+    first_content = content[1]
+    assert first_content.get("type") == "thinking", (
+        f"Second content must be 'thinking' type for Anthropic compatibility, "
+        f"but got '{first_content.get('type')}'"
+    )
+    expected_thinking = "We should use the city Tokyo as the city."
+    assert first_content.get("thinking") == expected_thinking, (
+        "Thinking content should be preserved"
+    )
+    # Signature should also be preserved
+    assert first_content.get("signature") == "TestSignature456", (
+        "Signature should be preserved in thinking block"
+    )
+
     # Verify tool calls are preserved
     tool_calls = assistant_msg.get("tool_calls", [])
     assert len(cast(list[Any], tool_calls)) == 1, "Tool calls should be preserved"