Two related bugs prevented users from reliably switching providers:
1. OPENAI_BASE_URL poisoning OpenRouter resolution: When a user with a
custom endpoint ran /model openrouter:model, _resolve_openrouter_runtime
picked up OPENAI_BASE_URL instead of the OpenRouter URL, causing model
validation to probe the wrong API and reject valid models.
Fix: skip OPENAI_BASE_URL when requested_provider is explicitly
'openrouter'.
2. Provider never saved to config: _save_model_choice() could save
config.model as a plain string. All five _model_flow_* functions then
checked isinstance(model, dict) before writing the provider — which
silently failed on strings. With no provider in config, auto-detection
would pick up stale credentials (e.g. Codex desktop app) instead of
the user's explicit choice.
Fix: _save_model_choice() now always saves as dict format. All flow
functions also normalize string->dict as a safety net before writing
provider.
Adds 4 regression tests. 2873 tests pass.
145c57fc01