Summary

Selecting a model from :model can persist an invalid (provider_id, model_id) pair when the chosen model belongs to a different provider than the current default provider.

This leaves Forge in a corrupted session state such as:

[session]
provider_id = "fireworks-ai"
model_id = "glm-5.1"

That pair is invalid because glm-5.1 belongs to the ZAI providers, not Fireworks.

Impact

• The UI can show one provider while the selected model belongs to another provider.
• Subsequent requests may route to an unexpected upstream.
• Error messages become misleading because the persisted config no longer reflects a valid provider/model pair.

Repro

1. Start Forge with a valid Fireworks provider selected.
2. Use :model and select glm-5.1 from the all-provider model picker.
3. Inspect ~/forge/.forge.toml.
4. Observe an invalid pair like:

[session]
provider_id = "fireworks-ai"
model_id = "glm-5.1"

Expected

Selecting a model from another provider should also switch the active provider, or the selection should be rejected.

Actual

Forge updates only the model, leaving the previous provider in place.

Notes

A local patch in crates/forge_main/src/ui.rs fixes this by resolving the selected model's owning provider and calling provider activation when the model crosses provider boundaries.