[Bug] Context truncation breaks function call/tool response pairing, causing Gemini 400 error

[Luna-channel]

What happened / 发生了什么

当对话历史中包含 function call（工具调用）时，ContextTruncator.fix_messages() 方法在截断消息时可能破坏 assistant(tool_calls) 和 tool response 的配对关系，导致 Gemini API 返回 400 错误。

根本原因分析：

astrbot/core/agent/context/truncator.py 的 fix_messages() 方法（第7-20行）只进行了单向检查：

• ✅ 检查 tool 消息前面是否有足够的消息
• ❌ 没有检查 包含 tool_calls 的 assistant 消息后面是否紧跟对应的 tool response

根据 OpenAI Chat Completions API 规范（Gemini 也遵循此规范），function call 必须紧跟 tool response。当截断发生在 assistant(tool_calls) 和 tool 之间时，会产生非法的消息序列，导致 API 拒绝请求。

Reproduce / 如何复现？

1. 使用 Gemini 作为 LLM 提供者
2. 在对话中触发工具调用（如使用 memes 插件、web-searcher 等）
3. 继续对话直到触发上下文截断（通过插件裁剪历史记录，或达到 token 限制触发压缩）
4. 如果截断后 assistant(含tool_calls) 消息后面不再紧跟 tool response，下次 LLM 请求会返回 400 错误

AstrBot version, deployment method (e.g., Windows Docker Desktop deployment), provider used, and messaging platform used. / AstrBot 版本、部署方式（如 Windows Docker Desktop 部署）、使用的提供商、使用的消息平台适配器

• AstrBot 版本: v4.18.2
• 部署方式: Docker
• LLM 提供商: Gemini (通过 OpenAI 兼容接口)
• 消息平台: aiocqhttp (OneBot v11)

OS

Linux

Logs / 报错日志

[2026-02-24 23:28:24.678] [Core] [WARN] [v4.18.2] [runners.tool_loop_agent_runner:249]: Chat Model 额度gemini request error: Error code: 400 - {'error': {'message': 'Please ensure that function call turn comes immediately after a user turn or after a function response turn.', 'type': 'upstream_error', 'param': '', 'code': 400}}
Traceback (most recent call last):
  File "/AstrBot/astrbot/core/agent/runners/tool_loop_agent_runner.py", line 224, in _iter_llm_responses_with_fallback
    async for resp in self._iter_llm_responses(include_model=idx == 0):
  File "/AstrBot/astrbot/core/agent/runners/tool_loop_agent_runner.py", line 201, in _iter_llm_responses
    yield await self.provider.text_chat(**payload)
  ...
openai.BadRequestError: Error code: 400 - {'error': {'message': 'Please ensure that function call turn comes immediately after a user turn or after a function response turn.', 'type': 'upstream_error', 'param': '', 'code': 400}}

消息序列日志（可以看到存在 assistant,user 的序列，如果该 assistant 包含 tool_calls 则格式非法）：

[AftCompact] RunCtx.messages -> [32] system,user,assistant,user,assistant,tool,assistant,user,assistant,tool,assistant,user,assistant,tool,assistant,user,assistant,user,assistant,user,assistant,user,assistant,user,assistant,user,assistant,user,assistant,user,assistant,user

Are you willing to submit a PR? / 你愿意提交 PR 吗？

• Yes!

Code of Conduct

• I have read and agree to abide by the project's Code of Conduct。

[DBJD-CR]

感觉我这个报错好像和你遇到的问题也是同根同源的🤔

LLM 响应错误: All chat models failed: BadRequestError: Error code: 400 - {'error': {'message': '* ***.tools[0].function_declarations[0].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[1].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[2].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[3].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[4].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[5].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[6].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[7].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[8].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[9].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[10].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[11].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[12].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[13].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[14].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[15].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[16].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[17].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[18].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[19].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[20].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[21].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[22].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[23].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[24].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[25].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[26].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[27].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[28].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[29].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[30].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[31].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[32].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[33].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[34].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[35].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[36].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[37].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[38].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[39].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[40].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[41].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[42].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[43].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n* ***.tools[0].function_declarations[44].name: Invalid function name. Must start with a letter or an underscore. Must be alphameric (a-z, A-Z, 0-9), underscores (_), dots (.), colons (:), or dashes (-), with a maximum length of 64.\n', 'type': 'upstream_error', 'param': '', 'code': 400}}

[DBJD-CR]

感觉我这个报错好像和你遇到的问题也是同根同源的🤔

有点奇怪，我这现在发现空@和主动回复（框架自带的概率回复）不会触发这个报错，但是一带消息@就稳定复现，不太确定有没有其他插件/MCP服务影响的问题。

主要这个报错说的内容是函数名不合规，但是检查了一遍发现没啥问题，以前也是能正常调用的，不太清楚具体是什么情况😵‍💫

[DBJD-CR]

@dosu 你觉得这些报错都是什么原因？

[dosubot]

根据你的分析和日志，这些报错的根本原因是同一个：

消息序列合法性被破坏。Gemini API 严格要求：

1. assistant(tool_calls) 后面必须紧跟 tool response
2. tool response 前面必须有对应的 assistant(tool_calls)

你的日志显示 assistant,user 这样的序列，说明如果该 assistant 包含 tool_calls，但其后的 tool response 被截断丢弃了，就会触发 400 错误。

从 fix_messages() 实现 来看，它只处理了"孤立的 tool 消息"（前面没有足够消息时清空），但没有处理"孤立的 assistant(tool_calls)"（后面没有 tool response 时应该移除该 assistant 消息）。

总结：所有报错都指向同一个 bug —— 单向检查逻辑不完整。

To reply, just mention @dosu.

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[Soulter]

#5417 fixed