fix(core): deduplicate switch-to-full logic, add missing mapper, mixed-AppType tests

Code review fixes:
- Extract duplicated 'switch to full' code block into local function SwitchToFull
- Add missing MaxChainBeforeFallback mapping in ConfigurationMapper
- Add 3 mixed-AppType test cases (Client+Upgrade split scenarios)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: JusterZhu