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/_utils.py

@@ -0,0 +1,25 @@
+"""_utils.py – shared helpers for file-ops tools."""
+
+from __future__ import annotations
+
+import posixpath
+
+_MAX_OUTPUT_LINES = 200
+_MAX_OUTPUT_CHARS = 20_000
+_TRUNCATION_NOTICE = "\n... [output truncated] ..."
+
+
+def truncate_output(output: str) -> str:
+    """Truncate *output* to avoid hitting token limits."""
+    lines = output.splitlines(keepends=True)
+    if len(lines) > _MAX_OUTPUT_LINES:
+        output = "".join(lines[:_MAX_OUTPUT_LINES]) + _TRUNCATION_NOTICE
+    if len(output) > _MAX_OUTPUT_CHARS:
+        output = output[:_MAX_OUTPUT_CHARS] + _TRUNCATION_NOTICE
+    return output
+
+
+def _parent(path: str) -> str:
+    """Return the parent directory of *path* (best-effort, no I/O)."""
+    parent = posixpath.dirname(path.rstrip("/"))
+    return parent or "."