Replay malformed historical tool input through Messages
通过 Messages 回放非法历史工具输入
Chat Completions retains tool arguments as strings, including malformed JSON from failed calls. Switching that history to Messages requires an object for each `tool_use.input`. Rejecting one historical argument blocks every later request containing it, even after a successful tool retry; a summarization request containing the same call also fails.
English
Problem
Chat Completions retains tool arguments as strings, including malformed JSON from failed calls. Switching that history to Messages requires an object for each tool_use.input. Rejecting one historical argument blocks every later request containing it, even after a successful tool retry; a summarization request containing the same call also fails.
Decision
The Messages serializer follows the pi-ai history conversion: malformed JSON and non-object values become {} only in the outgoing historical tool input. Call ids, names, results, and original Session records remain intact. This applies with valid, absent, or unusable native replay metadata and does not execute the historical call again.
This supersedes the historical argument rejection in the Messages adapter decision. New Messages responses still require valid object arguments before successful completion; output-limit truncation retains its existing pruning behavior. No Session event, persistence type, or protocol configuration changes.
Alternatives considered
Reject malformed history. A failed call can remain relevant evidence without preventing all subsequent model requests.
Repair or overwrite stored arguments. Guessing missing quotes or retaining a parsed prefix can change the requested operation. Request-only empty input preserves the original evidence and requires no migration.
Drop the call. Its result still cites the call id; keeping both preserves the tool exchange without inventing arguments.
Consequences
Messages continuation can omit unusable historical parameters without losing the call identity or result. The model sees {} rather than the original malformed text, and the fallback is silent, matching pi-ai. Original arguments remain available in the Session log; this does not claim lossless provider input or repair invalid newly generated calls.
Verification covers object-only conversion, failed results followed by user input, JSON round trips, both valid and degraded replay metadata, a recorded Session through the shipped headless profile and real Messages serializer, and a credential-gated live Messages continuation.
中文
问题
Chat Completions 将工具参数保留为字符串，其中可能包含失败调用产生的非法 JSON。将这段历史切换到 Messages 时，每个 tool_use.input 都必须是对象。拒绝一条历史参数就会阻断包含它的所有后续请求，即使工具重试已经成功；包含同一调用的摘要请求也会失败。
决策
Messages 序列化器 遵循 pi-ai 历史转换的做法：只在发出的历史工具输入中，将非法 JSON 和非对象值替换为 {}。调用 ID、名称、结果和原始 Session 记录保持不变。原生回放元数据有效、缺失或不可用时均采用此规则，也不会重新执行历史调用。
这取代了 Messages 适配器决策中的历史参数拒绝规则。新生成的 Messages 响应在成功完成前仍要求工具参数是有效对象；达到输出上限时仍按现有规则裁剪。不改变 Session 事件、持久化类型或协议配置。
考虑过的替代方案
拒绝非法历史。 失败调用可以继续作为相关证据保留，而不必阻断所有后续模型请求。
修复或覆盖已存参数。 猜测缺失的引号或保留部分解析结果可能改变请求的操作。只在请求中使用空输入可以保留原始证据，也不需要迁移。
删除调用。 对应结果仍引用调用 ID；同时保留调用和结果，可以保留工具交互而不编造参数。
后果
Messages 可以在省略不可用历史参数的同时继续会话，并保留调用身份和结果。模型看到的是 {}，而不是原始非法文本；该兜底与 pi-ai 一样不产生诊断。原始参数仍可在 Session 日志中查阅；这不保证提供方输入无损，也不修复新生成的非法调用。
验证覆盖仅接受对象的转换、失败结果后的用户输入、JSON 往返、有效与降级的回放元数据、通过已发布 headless profile 和真实 Messages 序列化器运行的录制 Session，以及需要凭据的真实 Messages 续接。