P0 Fixes:
- Enable toml `preserve_order` feature for reliable key ordering
- Extract pure detection functions to utils/commonConfigDetection.ts (fix layer inversion)
- Return structured result from preserveCodexConfigFormat to prevent data loss
P1 Fixes:
- Handle pure TOML strings in Codex config instead of silent skip
- Surface extractDiff errors in useCodexCommonConfig instead of swallowing
- Log parse errors in detectCommonConfigEnabledByContent for debugging
P2 Fixes:
- Use parsing-based assertions in Rust TOML ordering tests
- Add schema warning when Codex config field is wrong type
- Add depth/node limits to isSubset function (prevent stack overflow)
- Replace hardcoded "{}" check with adapter.hasValidContent()
P3 Fixes:
- Refactor Gemini errors to structured GeminiConfigErrorInfo format
- Add mapGeminiErrorToI18n for type-safe error-to-i18n mapping
- Add hasContent method to CommonConfigAdapter interface
- Move isSubset utility to configMerge.ts for reuse
- Export preserveCodexConfigFormat from adapters for hook use
- Add hasContentByAppType dispatcher for unified content detection
- Remove dead code from providerConfigUtils (hasCommonConfigSnippet,
hasTomlCommonConfigSnippet, hasGeminiCommonConfigSnippet)