Pass the user's models.json path to ModelRegistry so custom and non-built-in models (e.g. openrouter/qwen/qwen3.6-plus:free) are available when resolving the configured primary/fallback model. The pi CLI was already passing this path; kb was not, causing 'model not found in registry' errors for any model not built-in. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>