fix(webview): handle fast-mode guard bundle drift

[mkaoudis]

Summary

• teach the required fast-mode model guard patch to recognize the current upstream Array.isArray serviceTiers shape
• keep the existing null-safe Linux guard replacement so missing serviceTiers cannot crash the fast-mode availability hook
• add targeted patcher coverage for the drifted upstream bundle shape

Review order

This PR should be reviewed after #322. The code change itself is independent, but its Nix check is currently red only because main lacks #322's PR-only upstream DMG rollout handling. Once #322 lands, this PR should go green after rebase or rerun.

User-visible behavior

Linux app builds from the current upstream DMG should no longer fail required upstream patch validation because of the fast-mode guard shape.

Source of truth

• scripts/patches/webview-assets.js
• scripts/patch-linux-window-ui.test.js

Validation

Local validation:

• node --check scripts/patches/webview-assets.js
• node --test scripts/patch-linux-window-ui.test.js
• git diff --check origin/main...HEAD

GitHub validation on this draft PR:

• Build App Against Upstream DMG: pass
• Rust and Smoke Tests: pass
• Build Debian Package: pass
• Build RPM Package: pass
• Build Pacman Package: pass
• Nix Package Builds: fail only on the existing upstream Codex app version pin mismatch, which is addressed by fix(ci): tolerate upstream DMG rollout in PR Nix checks #322

Known scope

This only fixes the fast-mode required patch drift. It intentionally leaves unrelated remote-mobile and subagent drift handling to separate focused changes.

[ilysenko]

Thanks for putting this together. We are going to close this PR because the fast-mode guard drift has already been fixed on main by #336 with a broader matcher and additional coverage.

The failing Nix check here was not caused by this patch; it was the older upstream app version pin mismatch. However, the branch is now draft/conflicting and the functional fix has already landed, so keeping this PR open would only duplicate the current main implementation.

Thanks again for catching the upstream bundle drift.

[mkaoudis]

No problem! Happy to contribute when I run into stuff, thanks for reviewing :)