refactor: simplify resolveDefaultModel — always honor user config

As reviewers noted, the two conditions were logically redundant.
Simplified to: if user specified a model, always return it.
This makes the intent crystal clear.

Author: chaodu-agent

packages/opencode/src/acp/resolve-model.ts

@@ -3,20 +3,15 @@ import { ModelID, ProviderID } from "../provider/schema"
 /**
  * Pure resolution logic for choosing the default model.
  * Separated for testability — no SDK calls, no side effects.
+ *
+ * If the user specified a model in config.json, always honor it —
+ * regardless of whether the provider/model is currently loaded.
+ * This prevents falling through to Provider.sort() which may pick a paid model.
  */
 export function resolveDefaultModel(
   specified: { providerID: ProviderID; modelID: ModelID } | undefined,
   providers: Array<{ id: string; models: Record<string, unknown> }>,
 ): { providerID: ProviderID; modelID: ModelID } | undefined {
-  if (specified && providers.length) {
-    const provider = providers.find((p) => p.id === specified.providerID)
-    if (provider && provider.models[specified.modelID]) return specified
-    // Provider not yet loaded or model not found — still honor the user's explicit choice
-    // rather than falling through to Provider.sort() which may pick a paid model
-    if (!provider || !provider.models[specified.modelID]) return specified
-  }
-
-  if (specified && !providers.length) return specified
-
-  return undefined // let caller handle fallback
+  if (specified) return specified
+  return undefined
 }