Release-only loader_overrides unused_mut warning: scoped fix and verification

What version of Codex CLI is running?

Source build, codex-cli 0.0.0; base commit 455318c202.

What subscription do you have?

Not relevant to this source-build failure; subscription details not supplied.

Which model were you using?

Not applicable; compilation fails before model use.

What platform is your computer?

Arch Linux, x86_64-unknown-linux-gnu. Current host: Linux 7.2.3-arch1-2 x86_64 GNU/Linux.

What terminal emulator and version are you using (if applicable)?

Not supplied; failure occurs in the compiler/build system.

Codex doctor report

Not collected; this report concerns source compilation.

What issue are you seeing?

Release compilation emits:

warning: variable does not need to be mutable
    --> app-server/src/lib.rs:1377:5
1377 |     mut loader_overrides: LoaderOverrides,

This is the same warning reported in #29872 and #32939. This report supplies a separately published fix and debug/release verification for maintainers to consider alongside those reports.

What steps can reproduce the bug?

Build codex-app-server or a consuming codex-cli target with Cargo's release profile from the base revision above, after satisfying dependencies. The mutation is cfg-disabled in a normal release build, while the parameter remains mutable.

What is the expected behavior?

Release builds should avoid unused_mut, and debug builds should retain the test user-config override behavior.

Additional information

Root cause

In loader_overrides_with_test_user_config_file, loader_overrides.user_config_path is assigned only under cfg(debug_assertions). The parameter's mut declaration is unconditional, so release compilation removes the mutation but retains mutability.

Proposed fix and scope

Fix commit 827f92cf1c changes only codex-rs/app-server/src/lib.rs: keep the parameter immutable and shadow it as mutable under cfg(debug_assertions). This preserves debug behavior without suppressing the lint. The fork branch is based directly on upstream main and does not include the recursion-limit fix.

Verification

With this cleanup and the separate recursion-limit fix applied together:

• cargo check -p codex-app-server -p codex-exec -p codex-tui -p codex-cli passed.
• cargo build --release -p codex-cli passed and the reported loader_overrides warning was absent.

No test suite was run. The validation workspace also contained a local code-mode-runtime Cargo.toml adjustment; this validation does not establish clean-checkout V8 build support. No isolated warning-branch rebuild was performed after publishing the independent branch.

Sharing the root cause, patch, and results through an issue per the contribution guide; no upstream PR exists.

Start in codex-rs/app-server/src/lib.rs at loader_overrides_with_test_user_config_file, especially the parameter around lines 1376-1399 and its cfg(debug_assertions) mutation. Apply the scoped mutability fix described in the issue, then run cargo check -p codex-app-server -p codex-exec -p codex-tui -p codex-cli and cargo build --release -p codex-cli. Done means debug behavior remains available and the release build no longer emits the unused_mut warning.