Implement session-based conversation history for PrettyGeminiBot

[Copilot]

Modify Pretty Gemini Bot Conversation Logic ✅

• Understand the current implementation and Gemini API chat history
• Add environment variable for conversation history length
• Add conversation history array to PrettyGeminiBot class
• Modify get_response to create new chat session with history for each message
• Update clear method to clear conversation history
• Address all code review feedback
• Add constant for messages per round
• Improve message validation with explicit None checks
• Simplify code by removing unnecessary exception handling and checks
• Test the changes with mock API calls
• Run code style checks

Summary

Successfully implemented session-based conversation history management for PrettyGeminiBot:

• ✅ Each user message creates a new chat session with recent conversation history
• ✅ History length is configurable via PRETTY_GEMINI_BOT_HISTORY_LENGTH environment variable (default: 10 rounds)
• ✅ History is properly validated and limited to prevent excessive token usage
• ✅ Non-negative validation ensures history_length >= 0
• ✅ Messages are validated with explicit None checks before appending
• ✅ Clear method properly resets conversation history
• ✅ Code simplified based on review feedback
• ✅ All tests pass and code meets quality standards

Implementation Details

The bot now maintains conversation context through:

1. A conversation_history array that stores recent N rounds (configurable)
2. Creating a new chat session for each message with the recent history
3. Proper extraction and validation of new messages from the chat history
4. Using MESSAGES_PER_ROUND constant for maintainability
5. Simple and clean history slicing without unnecessary complexity

Original prompt

修改Pretty gemini bot的对话创建逻辑：每次用户发来新的对话都看成是一个新的session，需要通过gemini chats创建一个新的对话组，而不是在bot级维护。但是我们仍然需要有对话上下文，在bot的属性里面添加一个维护对话历史长度的数组，gemini chats.create支持一个history参数，这个history参数必须与是client.get_history拿到的数组类型一致。请通过一个环境变量来控制对话历史长度，并且在每次用户发来新的对话时候把最近的N轮历史加进去。在clear方法时候清空所有历史。

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Pull request overview

This PR implements session-based conversation history management for PrettyGeminiBot, enabling the bot to maintain context across multiple user interactions while creating a new chat session for each message.

Key changes:

• Added configurable conversation history tracking via PRETTY_GEMINI_BOT_HISTORY_LENGTH environment variable
• Refactored from persistent chat session to session-per-message approach with history
• Implemented automatic history management with recent N rounds preserved

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
mini_ema/bot/pretty_gemini_bot.py	Adds conversation history array, implements session-based chat creation with history parameter, updates clear() to reset history, and adds logic to extract and store new messages
.env.example	Documents the new PRETTY_GEMINI_BOT_HISTORY_LENGTH environment variable with default value of 10 rounds