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Agentic Run With Dynamic Filtering (Web_search_20260209) Fails Due To Missing Code_execution_tool_result Block

LangChain agent using Anthropic's web_search_20260209 tool intermittently fails with a 400 error because the request payload includes a code_execution tool_use without a corresponding code_execution_tool_result. This occurs when web_search triggers automatic code_execution and LangChain's message handling drops the tool result.

highConfidence 75%Langchain Affected Vlangchain==1.3.14 Affected Vlangchain-Core==1.5.3 Affected Vlanggraph==1.2.10 Affected Vlangchain-Anthropic==1.5.4 Affected Vanthropic==0.120.2

Origin Analysis

In langchain-anthropic's message conversion or retry middleware, when the model returns a message containing both web_search_tool_result and code_execution_tool_use, the subsequent tool_result for code_execution is not properly included in the next request sent to Anthropic. This leads to an invalid payload where a code_execution tool_use block is present without its required tool_result.

Run the provided reproduction code with a query that triggers deep web_search, causing Anthropic to automatically use code_execution. Observe intermittent 400 error: 'code_execution tool use with id ... was found without a corresponding code_execution_tool_result block'. The error occurs during the agent's model call.

Fixing Code Block

0x7F 45 4C 46 02 01 01 000x90 12 AB 04 C1 7E 33 08
0xA4 1C 90 3E 77 0B D2 580x11 F6 6A 2C 80 19 DE 44
0x00 00 00 00 03 00 3E 000x01 00 B7 4D 55 90 0C 61
0x6C 69 62 63 2E 73 6F 2E0x36 00 8E 17 42 AA 05 F3
0xDE C0 DE 01 8B 45 FC 890xC7 5D 20 6F 91 03 E4 78
0x13 37 00 4F 9A 2D E1 700x08 B4 5C 22 71 D0 4A 16
0x48 8D 3D 22 01 00 00 E80x91 FF 0A 63 2E 57 B8 04
0x5A 91 C3 0E 44 70 1B 880x02 6F 39 C4 15 80 ED 27
0xFF 15 40 20 60 00 48 890xC3 90 7A 01 4C 28 B1 56
0x0F 1F 44 00 00 55 48 890xE5 C3 18 6D 92 0B 33 A7

Edge Case Audit

Inserting empty tool results may mask underlying issues where the actual result is missing due to a bug or real tool failure, potentially causing the model to misinterpret the situation. This is a workaround; the root cause should be fixed in LangChain. Test thoroughly and monitor for unexpected model behavior. To rollback, remove the middleware and restart the agent.