feat: add AIO sandbox provider and auto title generation (#1)

- Add AioSandboxProvider for Docker-based sandbox execution with
  configurable container lifecycle, volume mounts, and port management
- Add TitleMiddleware to auto-generate thread titles after first
  user-assistant exchange using LLM
- Add Claude Code documentation (CLAUDE.md, AGENTS.md)
- Extend SandboxConfig with Docker-specific options (image, port, mounts)
- Fix hardcoded mount path to use expanduser
- Add agent-sandbox and dotenv dependencies

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/community/aio_sandbox/aio_sandbox.py

@@ -0,0 +1,113 @@
+import logging
+
+from agent_sandbox import Sandbox as AioSandboxClient
+
+from src.sandbox.sandbox import Sandbox
+
+logger = logging.getLogger(__name__)
+
+
+class AioSandbox(Sandbox):
+    """Sandbox implementation using the agent-infra/sandbox Docker container.
+
+    This sandbox connects to a running AIO sandbox container via HTTP API.
+    """
+
+    def __init__(self, id: str, base_url: str, home_dir: str | None = None):
+        """Initialize the AIO sandbox.
+
+        Args:
+            id: Unique identifier for this sandbox instance.
+            base_url: Base URL of the sandbox API (e.g., http://localhost:8080).
+            home_dir: Home directory inside the sandbox. If None, will be fetched from the sandbox.
+        """
+        super().__init__(id)
+        self._base_url = base_url
+        self._client = AioSandboxClient(base_url=base_url)
+        self._home_dir = home_dir
+
+    @property
+    def base_url(self) -> str:
+        return self._base_url
+
+    @property
+    def home_dir(self) -> str:
+        """Get the home directory inside the sandbox."""
+        if self._home_dir is None:
+            context = self._client.sandbox.get_context()
+            self._home_dir = context.home_dir
+        return self._home_dir
+
+    def execute_command(self, command: str) -> str:
+        """Execute a shell command in the sandbox.
+
+        Args:
+            command: The command to execute.
+
+        Returns:
+            The output of the command.
+        """
+        try:
+            result = self._client.shell.exec_command(command=command)
+            output = result.data.output if result.data else ""
+            return output if output else "(no output)"
+        except Exception as e:
+            logger.error(f"Failed to execute command in sandbox: {e}")
+            return f"Error: {e}"
+
+    def read_file(self, path: str) -> str:
+        """Read the content of a file in the sandbox.
+
+        Args:
+            path: The absolute path of the file to read.
+
+        Returns:
+            The content of the file.
+        """
+        try:
+            result = self._client.file.read_file(file=path)
+            return result.data.content if result.data else ""
+        except Exception as e:
+            logger.error(f"Failed to read file in sandbox: {e}")
+            return f"Error: {e}"
+
+    def list_dir(self, path: str, max_depth: int = 2) -> list[str]:
+        """List the contents of a directory in the sandbox.
+
+        Args:
+            path: The absolute path of the directory to list.
+            max_depth: The maximum depth to traverse. Default is 2.
+
+        Returns:
+            The contents of the directory.
+        """
+        try:
+            # Use shell command to list directory with depth limit
+            # The -L flag limits the depth for the tree command
+            result = self._client.shell.exec_command(command=f"find {path} -maxdepth {max_depth} -type f -o -type d 2>/dev/null | head -500")
+            output = result.data.output if result.data else ""
+            if output:
+                return [line.strip() for line in output.strip().split("\n") if line.strip()]
+            return []
+        except Exception as e:
+            logger.error(f"Failed to list directory in sandbox: {e}")
+            return []
+
+    def write_file(self, path: str, content: str, append: bool = False) -> None:
+        """Write content to a file in the sandbox.
+
+        Args:
+            path: The absolute path of the file to write to.
+            content: The text content to write to the file.
+            append: Whether to append the content to the file.
+        """
+        try:
+            if append:
+                # Read existing content first and append
+                existing = self.read_file(path)
+                if not existing.startswith("Error:"):
+                    content = existing + content
+            self._client.file.write_file(file=path, content=content)
+        except Exception as e:
+            logger.error(f"Failed to write file in sandbox: {e}")
+            raise