fix(usage): honor provider-aware pricing precedence

tests/unit/model-pricing.test.ts

@@ -327,6 +327,11 @@ describe('model-pricing', () => {
               name: 'GPT-5.5',
               cost: { input: 5, output: 30, cache_read: 0.5 },
             },
+            'gpt-4o': {
+              id: 'gpt-4o',
+              name: 'GPT-4o',
+              cost: { input: 2.5, output: 10, cache_read: 1.25 },
+            },
             'openai-exclusive-model': {
               id: 'openai-exclusive-model',
               name: 'OpenAI Exclusive Model',
@@ -343,6 +348,11 @@ describe('model-pricing', () => {
               name: 'GPT-5.5',
               cost: { input: 0, output: 0 },
             },
+            'gpt-4o': {
+              id: 'gpt-4o',
+              name: 'GPT-4o',
+              cost: { input: 0, output: 0 },
+            },
           },
         },
       });
@@ -371,6 +381,13 @@ describe('model-pricing', () => {
       expect(pricing.outputPerMillion).toBe(0);
     });
 
+    it('prefers provider-aware models.dev pricing over exact static table matches', () => {
+      const pricing = getModelPricing('gpt-4o', { provider: 'github-copilot' });
+      expect(pricing.inputPerMillion).toBe(0);
+      expect(pricing.outputPerMillion).toBe(0);
+      expect(getModelPricing('gpt-4o').inputPerMillion).toBe(2.5);
+    });
+
     it('does not use ambiguous model-only models.dev matches', () => {
       const pricing = getModelPricing('gpt-5.5');
       expect(pricing).toEqual(getModelPricing('unknown-model-xyz'));