Revert "chore: review in read-only (#7593)" (#8127)

This reverts commit 291b54a762.

This commit was intended to prevent the model from making code changes
during `/review`, which is sometimes does. Unfortunately, it has other
unintended side effects that cause `/review` to fail in a variety of
ways. See #8115 and #7815. We've therefore decided to revert this
change.

codex-rs/core/tests/suite/review.rs

@@ -580,10 +580,6 @@ async fn review_input_isolated_from_parent_history() {
         review_prompt,
         "user message should only contain the raw review prompt"
     );
-    assert!(
-        env_text.contains("<sandbox_mode>read-only</sandbox_mode>"),
-        "review environment context must run with read-only sandbox"
-    );
 
     // Ensure the REVIEW_PROMPT rubric is sent via instructions.
     let instructions = body["instructions"].as_str().expect("instructions string");