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/read_file.py

@@ -0,0 +1,60 @@
+"""read_file.py – tool for reading files inside the sandbox."""
+
+from __future__ import annotations
+
+from shlex import quote
+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_read_file_tool(sandbox: "DockerSandbox") -> BaseTool:
+    """Return a read_file tool bound to *sandbox*."""
+
+    @tool
+    def read_file(path: str, offset: int = 0, length: int = 5000) -> str:
+        """
+        Read a file at *path*.
+
+        *path* can be absolute (``/tmp/re-agent/result.csv``) or relative to the
+        working directory.
+
+        *offset* is the number of bytes to skip from the start of the file.
+        *length* is the maximum number of bytes to return.  If the file is
+        longer than ``offset + length``, the
+        output is trimmed and a summary line is appended showing how many
+        bytes were omitted.
+
+        Returns the (possibly trimmed) file contents as text, or an error message.
+        """
+        logger.debug(
+            "Reading file inside sandbox: {} offset={} length={}", path, offset, length
+        )
+        exit_code, wc_out = sandbox.exec(f"wc -c -- {quote(path)}")
+        if exit_code != 0:
+            return f"[ERROR reading {path!r}] {wc_out.strip()}"
+        try:
+            total = int(wc_out.split()[0])
+        except (ValueError, IndexError):
+            return f"[ERROR parsing file size for {path!r}] {wc_out.strip()}"
+
+        exit_code, chunk = sandbox.exec(
+            f"dd if={quote(path)} iflag=skip_bytes,count_bytes"
+            f" skip={offset} count={length} 2>/dev/null"
+        )
+        if exit_code != 0:
+            return f"[ERROR reading {path!r}] {chunk.strip()}"
+
+        suffix = ""
+        if offset + length < total:
+            remaining = total - (offset + length)
+            suffix = f"\n[... {remaining} more bytes not shown (total {total} bytes). Use offset/length to read further.]"
+        elif offset > 0 or total > length:
+            suffix = f"\n[File total: {total} bytes, showing {len(chunk)} chars from offset {offset}.]"
+        return chunk + suffix
+
+    return read_file