_make_agent() was not calling resolve_runtime_provider(), so bare-slug models (e.g. 'claude-opus-4-6' with provider: anthropic) left provider, base_url, and api_key empty in AIAgent — causing HTTP 404 at api.anthropic.com. Now mirrors cli.py: calls resolve_runtime_provider(requested=None) and forwards all 7 resolved fields to AIAgent. Adds regression test.