[LLM:Feature] Add Agentic Flow to MNN LLM Chat

[huangzhengxiang]

Description

This PR adds an optional Agent mode to MNN LLM Chat while preserving the existing normal chat flow. Agent mode can use host-provided tools for web search,built-in browser reading, Python execution, workspace files, memory, and skill updates. Normal sessions remain backward compatible and continue using the original path when Agent mode is not enabled.

Changes

• Added per-session Agent mode selection for new conversations.
• Persisted session-level Agent metadata with database migration and backward compatibility for existing sessions.
• Added an agentic loop in ChatPresenter:
  • Parses model-emitted system_calls.
  • Executes tool calls step by step.
  • Feeds observations back into the same conversation.
  • Supports visible progress, continuation, budget limits, and stop control.
• Added robust output parsing for imperfect model JSON:
  • fenced JSON blocks
  • single tool objects
  • nested system_calls arrays
  • loose python_exec recovery
• Added built-in tools:
  • web_search
  • browser_url
  • python_exec
  • get_current_time
• Added lightweight Python runtime integration through Chaquopy.
• Added workspace-aware Python helpers for file generation, including Excel output.
• Added generated file detection and attachment handling for chat replies.
• Added an in-app workspace file browser from chat history.
• Added memory and skill persistence with filtering/compaction to avoid noisy one-off updates.
• Updated native session handling to better support prompt cache/KV-cache continuation for Agent turns.
• Added token/performance display for assistant messages.
• Added docs for Agent design, built-in browser, built-in Python, memory/skill, development notes, and future iteration.
• Ignored local Android/CMake build artifacts such as .cxx/ and app/standard/.

Notes

• Existing non-Agent conversations should continue to use the old chat path.
• Agent mode is selected when creating a new conversation and then persists with that session.
• Python file outputs are resolved inside the app workspace and surfaced back into chat when possible.
• The workspace browser now uses the app's internal file browser instead of relying on system file-manager folder intents.

Testing

• Manual device testing was used during development for:
  • Agent mode selection
  • web/browser tool calls
  • Python execution
  • Excel file generation
  • generated file return in chat
  • workspace file browsing
  • session restore/history behavior

Module

MNN Chat

Type

• Feature
• Bugfix
• Perf
• Refact
• Style
• Doc
• Test
• Chore

Checklist

• Commit message follows [Module:Type] Description format
• Code compiles without errors
• Tested on relevant platform(s)
• No unrelated format or style changes included

[wangzhaode]

Review Summary

这个 PR 为 Android MNN LLM Chat 添加了 Agent 模式，包括 web search、Python 执行、浏览器读取等工具调用能力。代码完全在 apps/Android/MnnLlmChat/ 目录下，不影响 MNN 核心引擎。

需要关注的点

1. Chaquopy 依赖：引入了 com.chaquo.python 插件（Python on Android），会显著增加 APK 体积。确认是否只在特定 flavor 中启用，以及是否有无 Python 的降级方案。

2. 安全性：python_exec 工具在设备上执行模型生成的 Python 代码，存在安全风险。建议添加沙箱限制（禁止网络访问、文件系统访问范围限制等）。

3. Agent loop 限制：确认是否有最大迭代次数限制防止无限循环（budget limits 在描述中提到了，很好）。

4. 数据库迁移：新增 Agent 相关字段需要确保向后兼容（老版本数据库升级不崩溃）。

5. build.gradle 格式：从 build.gradle.kts（Kotlin DSL）变成了 build.gradle（Groovy），这是有意的重构还是冲突？请确认。

6. C++ JNI 层改动：llm_session.cpp 和 llm_mnn_jni.cpp 有少量改动，需要确认不影响现有 chat 流程。

7. 文档完善 ✅：docs/ 目录下有完整的设计文档。

建议

• 等 @Juude 的 review 完成后再决定合入
• 确认格式检查失败的原因并修复
• 本 PR 不涉及引擎层改动，主要需要 Android 应用侧的测试验证

[Juude]

apps/Android/MnnLlmChat/docs/Agent.gif 这个 gif 太大了，可以找个在线裁剪平台裁剪下，然后邮件发我下，我上传到 cdn

[huangzhengxiang]

apps/Android/MnnLlmChat/docs/Agent.gif 这个 gif 太大了，可以找个在线裁剪平台裁剪下，然后邮件发我下，我上传到 cdn

发你的gmail邮箱了，压缩完2.8MB

[Juude]

apps/Android/MnnLlmChat/docs/Agent.gif 这个 gif 太大了，可以找个在线裁剪平台裁剪下，然后邮件发我下，我上传到 cdn

发你的gmail邮箱了，压缩完2.8MB

可以直接用这个 cdn 地址： https://meta.alicdn.com/data/mnn/assets/Agent.gif

[huangzhengxiang]

apps/Android/MnnLlmChat/docs/Agent.gif 这个 gif 太大了，可以找个在线裁剪平台裁剪下，然后邮件发我下，我上传到 cdn

发你的gmail邮箱了，压缩完2.8MB

可以直接用这个 cdn 地址： https://meta.alicdn.com/data/mnn/assets/Agent.gif

已更新，把原有gif删了。