Merge Gateway reasoning effort variants are not selectable #41868

Description

Merge Gateway models can declare supported reasoning efforts through models.dev, but OpenCode does not map merge-gateway-ai-sdk-provider to the adapter's mergeGateway provider-options namespace.

As a result, the declared effort variants are unavailable and a selected effort is not forwarded to the adapter.

Expected behavior: expose the exact effort values declared by models.dev and send the selected value through providerOptions.mergeGateway.reasoningEffort.

Related PR: #41867

Plugins

None

OpenCode version

Development build at d470434

Steps to reproduce

1. Connect the MERGE Gateway provider.
2. Select a reasoning model such as GPT-5.6 Sol.
3. Open the model variant selector.
4. Observe that the reasoning effort choices declared by models.dev are unavailable.

Screenshot and/or share link

Operating System

macOS 26.5.2

Terminal

Ghostty