fix(core): 将用户拒绝工具执行原因写入模型上下文

[hanydd]

背景

现在ReactAgent和HarnessAgent已经有工具审批逻辑，发出 RequireUserConfirmEvent 和 UserConfirmResultEvent事件，用户可以选择通过或者拒绝，但是没有渠道可以把用户主动提供的拒绝调用的原因。已合并的 #2511 建立了工具审批结果的事件和恢复链路，但 ConfirmResult 只能表达通过或拒绝，拒绝时写入模型上下文的仍是固定文案，无法携带用户主动提供的原因。这个PR拓展了一下工具调用审批需要的 ConfirmResult，加入了可选的reason字段，并且将原因加入到了对应的ToolResultBlock里面。

改动

• 为 ConfirmResult 增加可选 reason，保留旧构造函数。
• 拒绝时将原因追加到 DENIED 工具结果，使模型下一轮可见。
• 补充 ReActAgent 上下文测试和 Harness 远程事件编解码测试。

测试

ReActAgentHitlTest、RemoteEventCodecPassthroughTest 通过。

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[AgentScopeJavaBot]

🤖 AI Review

This PR adds an optional reason field to ConfirmResult so that when a user denies a tool call in the HITL (Human-In-The-Loop) flow, their explanation is propagated into the model's context as part of the DENIED tool result message. The implementation is backward-compatible (new overloaded constructors, @JsonInclude(NON_NULL) on the getter, @JsonCreator handles missing reason as null). Two well-targeted tests cover the core path (reason appears in denied tool result text) and the codec round-trip (reason survives serialization). The change is small, focused, and solves a real usability gap — without it, the model has no idea why the user rejected a tool call.

[AgentScopeJavaBot]

🤖 AI Review

This PR adds an optional reason field to ConfirmResult so that when a user denies a tool call in the HITL (Human-In-The-Loop) flow, their explanation is propagated into the model's context as part of the DENIED tool result message. The implementation is backward-compatible (new overloaded constructors, @JsonInclude(NON_NULL) on the getter, @JsonCreator handles missing reason as null). Two well-targeted tests cover the core path (reason appears in denied tool result text) and the codec round-trip (reason survives serialization). The change is small, focused, and solves a real usability gap — without it, the model has no idea why the user rejected a tool call.

[hanydd]

@chickenlj 大佬可以看下这个PR吗？改动不大，主要是加了工具审批的时候，可以让调用方把用户拒绝工具执行的原因传进来。目前项目中用到了这个功能，现在只能在外面再加适配层，才能把用户的原因拼进去。