fix: model cost overrides

packages/opencode/src/provider/provider.ts

@@ -272,14 +272,20 @@ export namespace Provider {
           reasoning: model.reasoning ?? existing?.reasoning ?? false,
           temperature: model.temperature ?? existing?.temperature ?? false,
           tool_call: model.tool_call ?? existing?.tool_call ?? true,
-          cost: {
-            ...existing?.cost,
-            ...model.cost,
-            input: 0,
-            output: 0,
-            cache_read: 0,
-            cache_write: 0,
-          },
+          cost:
+            !model.cost && !existing?.cost
+              ? {
+                  input: 0,
+                  output: 0,
+                  cache_read: 0,
+                  cache_write: 0,
+                }
+              : {
+                  cache_read: 0,
+                  cache_write: 0,
+                  ...existing?.cost,
+                  ...model.cost,
+                },
           options: {
             ...existing?.options,
             ...model.options,