feat: add auto context compress ability for agent

[Lerr1uqs]

Related Issue

Description

Purpose / 目的

This PR introduces ACC (Auto Context Compress) mode to give the agent the ability to
autonomously decide when to compact context, so it can sustain longer-running tasks
with better continuity and less context exhaustion.

本 PR 引入 ACC（Auto Context Compress）模式，核心目标是让 agent 具备
自主判断上下文压缩时机的能力，从而支持更长时间连续作业，
减少上下文耗尽导致的中断与退化。

Why this matters / 为什么重要

• Fixed-threshold compaction is reactive and may miss the best timing.

• In long workflows, the agent often has better local judgment on when older context becomes
  low-value.

• ACC adds runtime context-capacity awareness and controlled compaction access, enabling
  proactive compression while preserving task continuity.

• 固定阈值压缩偏被动，触发时机不一定最优。

• 在长链路任务中，agent 往往更清楚哪些历史上下文已经低价值。

• ACC 提供运行时容量感知和受控压缩能力，让 agent 能主动压缩并保持任务连续性。

What changed / 改动内容

1. Added /acc slash command (toggle/on/off/status).

2. Added ACC mode indicator (ACC) in shell bottom toolbar.

3. When ACC is enabled, each LLM step appends a lightweight runtime hint including:

   • context used / max
   • remaining capacity
   • safe remaining capacity (after reserved budget)
   • reminder that the model may call the ACC compaction tool

4. Added AccCompactContext tool:

   • hidden by default
   • only exposed when ACC mode is enabled
   • requires task_summary

5. Reused existing compaction pipeline and extended it to append task_summary after compaction
   so post-compaction behavior remains aligned with current task progress.

6. 新增 /acc 斜杠命令（切换/开启/关闭/状态）。

7. 在 Shell 底栏新增 ACC 模式标记（ACC）。

8. ACC 开启时，每次 LLM step 前附加轻量提示，包括：

   • 当前上下文已用/上限
   • 剩余容量
   • 安全剩余容量（扣除保留预算后）
   • 提醒模型可调用 ACC 压缩工具

9. 新增 AccCompactContext 工具：

   • 默认隐藏
   • 仅在 ACC 开启时暴露
   • 必填 task_summary

10. 复用现有压缩链路，并在压缩后追加 task_summary，
    确保压缩后仍能按当前任务进度继续执行。

Non-invasive implementation / 非侵入式实现原则

• No large refactor in agent spec or tool loading architecture.

• ACC logic is added incrementally around existing KimiSoul flow and current compaction
  mechanisms.

• Existing /compact behavior is preserved.

• 不改动 agent spec 与工具加载主架构。

• ACC 仅在现有 KimiSoul 与压缩流程外围做增量扩展。

• 现有 /compact 行为保持不变。

Tests / 测试

Added/updated focused tests:

• tests/core/test_acc_tool.py
• tests/core/test_kimisoul_slash_commands.py
• tests/ui_and_conv/test_prompt_tips.py

Validation command:

uv run pytest tests/core/test_acc_tool.py tests/core/test_kimisoul_slash_commands.py tests/ui_and_conv/test_prompt_tips.py

Result: all passed.

Checklist

• I have read the CONTRIBUTING document.
• I have linked the related issue, if any.
• I have added tests that prove my fix is effective or that my feature works.
• I have run make gen-changelog to update the changelog.
• I have run make gen-docs to update the user documentation.

---