Preserve requested approval reviewers across policy overrides (#59272)

## Why

A model requirement can force `auto_review` even when the requested reviewer is `user`. Persisting or sending that effective value back as an explicit choice loses the original selection, so removing the requirement cannot restore it on resume.

## What changed

- Retain `requested_approvals_reviewer` separately from the effective reviewer in configuration and thread settings, with a fallback for older histories.
- Restore the requested reviewer on resume while applying current model requirements and reviewer allowlists.
- Let ordinary TUI turns, continuations, retries, and forks inherit the server's reviewer instead of echoing its effective value as an explicit request.
- Preserve a worker's requested reviewer when reloading it rather than inheriting the sender's selection.

## Testing

Extend resume coverage for explicit `auto_review`, removal of a model requirement, and a tightened reviewer allowlist. Update TUI assertions for omitted reviewer overrides and verify worker reload preserves its reviewer.

GitOrigin-RevId: d8c9c3a7b89e55e63f0e8ae210d6a87cb5547933

codex-rs/core/src/codex_thread.rs

@@ -161,6 +161,8 @@ pub struct CodexThreadSettingsOverrides {
     pub profile_workspace_roots: Option<Vec<ProfileWorkspaceRoot>>,
     pub approval_policy: Option<AskForApproval>,
     pub approvals_reviewer: Option<ApprovalsReviewer>,
+    /// Retained selection when restoring an effective reviewer forced by policy.
+    pub requested_approvals_reviewer: Option<ApprovalsReviewer>,
     pub sandbox_policy: Option<SandboxPolicy>,
     pub permission_profile: Option<PermissionProfile>,
     pub active_permission_profile: Option<ActivePermissionProfile>,
@@ -877,6 +879,7 @@ impl CodexThread {
             profile_workspace_roots,
             approval_policy,
             approvals_reviewer,
+            requested_approvals_reviewer,
             sandbox_policy,
             permission_profile,
             active_permission_profile,
@@ -890,6 +893,7 @@ impl CodexThread {
             disabled_plugin_ids,
         } = overrides;
         SessionSettingsUpdate {
+            requested_approvals_reviewer,
             turn_extension_init,
             step_settings: StepSettingsUpdate {
                 model,