Add a feature flag to preserve apply_patch line endings (#37758)

## What changed

- Add the `apply_patch_preserve_line_endings` feature, disabled by default, to
  preserve CRLF, CR, and mixed line endings when `apply_patch` updates files.
- Apply the feature consistently to built-in patch handling and patches invoked
  through shell, user-shell, unified-exec, and app-server command execution.
- Keep the active feature configuration authoritative over inherited, shell
  snapshot, and client-provided environment values.

## Testing

- Cover line-ending behavior with the feature enabled and disabled for custom
  tool calls, shell heredocs, command execution, and the `apply_patch` CLI.

GitOrigin-RevId: 531a7c66761959c650270559f57941929f03e6c4

codex-rs/features/src/lib.rs

@@ -123,6 +123,8 @@ pub enum Feature {
     TerminalVisualizationInstructions,
     /// Stream structured progress while apply_patch input is being generated.
     ApplyPatchStreamingEvents,
+    /// Preserve existing line endings when apply_patch updates files.
+    ApplyPatchPreserveLineEndings,
     /// Allow exec tools to request additional permissions while staying sandboxed.
     ExecPermissionApprovals,
     /// Expose the built-in request_permissions tool.
@@ -1045,6 +1047,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::UnderDevelopment,
         default_enabled: false,
     },
+    FeatureSpec {
+        id: Feature::ApplyPatchPreserveLineEndings,
+        key: "apply_patch_preserve_line_endings",
+        stage: Stage::UnderDevelopment,
+        default_enabled: false,
+    },
     FeatureSpec {
         id: Feature::ExecPermissionApprovals,
         key: "exec_permission_approvals",