feat: Initial library extraction from PIN LLM benchmark

DockerSandbox + LangChain file/shell tools extracted into a standalone package.

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

docker_agent_sandbox/tools/write_file.py

@@ -0,0 +1,32 @@
+"""write_file.py – tool for writing files inside the sandbox."""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from langchain_core.tools import BaseTool, tool
+from loguru import logger
+
+if TYPE_CHECKING:
+    from docker_agent_sandbox.sandbox import DockerSandbox
+
+
+def make_write_file_tool(sandbox: "DockerSandbox") -> BaseTool:
+    """Return a write_file tool bound to *sandbox*."""
+
+    @tool
+    def write_file(path: str, content: str) -> str:
+        """
+        Write *content* to *path*.
+
+        *path* can be absolute or relative.  Parent directories are created
+        automatically.  Returns a confirmation message or an error.
+        """
+        try:
+            logger.debug("Writing file inside sandbox: {}", path)
+            sandbox.write_file(path, content)
+        except Exception as exc:
+            return f"[ERROR writing {path!r}] {exc}"
+        return f"[OK] Written {len(content.encode())} bytes to {path}"
+
+    return write_file