feat: 新增 core/agents 模块和 nanobot

- 新增 agents 模块，包含 agent、api、skills 等子模块
- 新增 nanobot 项目，支持多渠道集成
- 添加启动脚本 start-all.bat 和 start-all.sh

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

core/agents/agent/context.py

@@ -0,0 +1,111 @@
+"""Context builder for assembling agent prompts."""
+
+import platform
+from pathlib import Path
+from typing import Any
+
+
+class ContextBuilder:
+    """Builds the context (system prompt + messages) for the agent."""
+
+    def __init__(self, workspace: Path):
+        """Initialize the context builder.
+
+        Args:
+            workspace: Workspace directory
+        """
+        self.workspace = workspace
+
+    def build_system_prompt(self) -> str:
+        """Build the system prompt with identity and runtime info."""
+        workspace_path = str(self.workspace.expanduser().resolve())
+        system = platform.system()
+        runtime = f"{system} {platform.machine()}"
+
+        return f"""# X-Agents Assistant
+
+You are an AI assistant built on the X-Agents platform.
+
+## Runtime
+{runtime}
+
+## Workspace
+Your workspace is at: {workspace_path}
+
+## Guidelines
+- Be helpful and concise
+- Think step by step when needed
+- Ask for clarification when the request is ambiguous
+"""
+
+    def build_messages(
+        self,
+        history: list[dict[str, Any]],
+        current_message: str,
+    ) -> list[dict[str, Any]]:
+        """Build the complete message list for an LLM call.
+
+        Args:
+            history: Conversation history
+            current_message: Current user message
+
+        Returns:
+            List of messages for LLM
+        """
+        return [
+            {"role": "system", "content": self.build_system_prompt()},
+            *history,
+            {"role": "user", "content": current_message},
+        ]
+
+    def add_assistant_message(
+        self,
+        messages: list[dict[str, Any]],
+        content: str | None,
+        tool_calls: list[dict[str, Any]] | None = None,
+        reasoning_content: str | None = None,
+    ) -> list[dict[str, Any]]:
+        """Add an assistant message to the message list.
+
+        Args:
+            messages: Current message list
+            content: Assistant message content
+            tool_calls: Optional tool calls
+            reasoning_content: Optional reasoning from model
+
+        Returns:
+            Updated message list
+        """
+        msg = {"role": "assistant", "content": content or ""}
+        if tool_calls:
+            msg["tool_calls"] = tool_calls
+        if reasoning_content:
+            msg["reasoning_content"] = reasoning_content
+        messages.append(msg)
+        return messages
+
+    def add_tool_result(
+        self,
+        messages: list[dict[str, Any]],
+        tool_call_id: str,
+        tool_name: str,
+        result: str,
+    ) -> list[dict[str, Any]]:
+        """Add a tool result to the message list.
+
+        Args:
+            messages: Current message list
+            tool_call_id: ID of the tool call
+            tool_name: Name of the tool
+            result: Tool execution result
+
+        Returns:
+            Updated message list
+        """
+        messages.append({
+            "role": "tool",
+            "tool_call_id": tool_call_id,
+            "name": tool_name,
+            "content": result,
+        })
+        return messages