v0.3.63

Fixed

• Fixed startup model resolution ignoring extension-provided default providers: CodingAgent::session() resolved the startup model before loading extensions, so when settings.json configured an extension provider as defaultProvider (e.g. antigravity), resolution failed to find the unregistered provider and fell back to direct built-ins (e.g. google/gemini-3.8-flash). Extensions and custom providers are now loaded before model resolution runs.