fix: respect cfg.provider filter in altimate-backend default model check

The altimate-backend early return was bypassing the cfg.provider
constraint that the generic fallback respects. Now the altimate check
only triggers if altimate-backend is in the user's configured provider
set (or if no provider filter is configured).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mdesmet

packages/opencode/src/provider/provider.ts

@@ -1638,10 +1638,15 @@ export namespace Provider {
     }
 
     // altimate_change start — default to altimate-backend when configured and no model chosen yet
-    const altimateProvider = providers[ProviderID.make("altimate-backend")]
-    if (altimateProvider && altimateProvider.models[ModelID.make("altimate-default")]) {
+    const altimateProviderID = ProviderID.make("altimate-backend")
+    const altimateProvider = providers[altimateProviderID]
+    if (
+      altimateProvider &&
+      altimateProvider.models[ModelID.make("altimate-default")] &&
+      (!cfg.provider || Object.keys(cfg.provider).includes(String(altimateProviderID)))
+    ) {
       return {
-        providerID: ProviderID.make("altimate-backend"),
+        providerID: altimateProviderID,
         modelID: ModelID.make("altimate-default"),
       }
     }