core: add a sandbox-backed fs helper

codex-rs/fs-ops/src/command_tests.rs

@@ -0,0 +1,21 @@
+use super::FsCommand;
+use super::READ_FILE_OPERATION_ARG2;
+use super::parse_command_from_args;
+use pretty_assertions::assert_eq;
+
+#[test]
+fn parse_read_command() {
+    let command = parse_command_from_args(
+        [READ_FILE_OPERATION_ARG2, "/tmp/example.png"]
+            .into_iter()
+            .map(Into::into),
+    )
+    .expect("command should parse");
+
+    assert_eq!(
+        command,
+        FsCommand::ReadFile {
+            path: "/tmp/example.png".into(),
+        }
+    );
+}