fix: preserve dash-prefixed sandbox copy paths

baseten/sandbox/_fs.py

@@ -1048,7 +1048,8 @@ def _copy_command(source: str, destination: str) -> str:
     quoted = [
         "'" + value.replace("'", "'\\''") + "'" for value in (source, destination)
     ]
-    return f"cp -r {quoted[0]} {quoted[1]}"
+    # End option parsing so relative paths beginning with - remain operands.
+    return f"cp -r -- {quoted[0]} {quoted[1]}"
 
 
 def _watch_path(path: str, recursive: bool | None) -> str:

tests/sandbox/test_copy_paths.py

@@ -0,0 +1,49 @@
+from __future__ import annotations
+
+import subprocess
+from pathlib import Path
+
+import httpx
+import pytest
+
+from tests.sandbox.test_fs import _body, _Fake, _ok, _process
+
+
+@pytest.mark.parametrize("asynchronous", [False, True])
+@pytest.mark.parametrize(
+    ("source", "destination"),
+    [("-source", "copy"), ("source", "-destination"), ("-source", "-destination")],
+)
+@pytest.mark.asyncio
+async def test_copy_preserves_paths_starting_with_dash(
+    tmp_path: Path, source: str, destination: str, asynchronous: bool
+) -> None:
+    (tmp_path / source).write_text("file contents")
+
+    def handle(request: httpx.Request) -> httpx.Response:
+        if request.method == "POST":
+            # Execute the SDK's actual command against local fixture files.
+            result = subprocess.run(
+                _body(request)["command"],
+                shell=True,
+                check=False,
+                cwd=tmp_path,
+                capture_output=True,
+                text=True,
+                timeout=5,
+            )
+            return _ok(
+                _process(
+                    status="completed" if result.returncode == 0 else "failed",
+                    exitCode=result.returncode,
+                    stderr=result.stderr,
+                )
+            )
+        return _ok(_process())
+
+    fake = _Fake(handle)
+    if asynchronous:
+        await fake.async_sandbox().fs.copy(source=source, destination=destination)
+    else:
+        fake.sandbox().fs.copy(source=source, destination=destination)
+    assert (tmp_path / destination).read_text() == "file contents"

tests/sandbox/test_fs.py

@@ -646,7 +646,9 @@ def handle(request: httpx.Request) -> httpx.Response:
 
         fake = _Fake(handle)
         fake.sandbox().fs.copy(source="/tmp/it's", destination="/tmp/b c")
-        assert _body(fake.requests[0])["command"] == "cp -r '/tmp/it'\\''s' '/tmp/b c'"
+        assert (
+            _body(fake.requests[0])["command"] == "cp -r -- '/tmp/it'\\''s' '/tmp/b c'"
+        )
         assert _path(fake.requests[1]) == "/process/7"
 
     @pytest.mark.parametrize(