fix: review

Author: NikolaiSviridov

src/CodexAcpClient.ts

@@ -355,18 +355,31 @@ export class CodexAcpClient {
         reasoningEffort: ReasoningEffort | null,
         serviceTier: ServiceTier | null,
     ): ModelSelection {
-        const selectedModel =
-            availableModels.find(m => m.id === modelId) ??
-            availableModels.find(m => m.isDefault);
+        const requestedModel = availableModels.find(m => m.id === modelId);
+        const selectedModel = requestedModel ?? availableModels.find(m => m.isDefault);
 
         if (!selectedModel) {
             throw new Error(`Model selection failed: No model found for ID "${modelId}" and no default model is defined.`);
         }
 
+        const supportedReasoningEfforts = selectedModel.supportedReasoningEfforts ?? [];
+        const additionalSpeedTiers = selectedModel.additionalSpeedTiers ?? [];
+        const selectedReasoningEffort = reasoningEffort !== null && supportedReasoningEfforts.some(
+            option => option.reasoningEffort === reasoningEffort
+        )
+            ? reasoningEffort
+            : selectedModel.defaultReasoningEffort;
+        const didSelectRequestedModel = requestedModel !== undefined;
+        const supportsServiceTier = serviceTier !== null && additionalSpeedTiers.includes(serviceTier);
+        const selectedServiceTier =
+            didSelectRequestedModel && supportsServiceTier
+                ? serviceTier
+                : null;
+
         return {
             currentModelId: selectedModel.id,
-            currentReasoningEffort: reasoningEffort ?? selectedModel.defaultReasoningEffort,
-            currentServiceTier: serviceTier ?? null,
+            currentReasoningEffort: selectedReasoningEffort,
+            currentServiceTier: selectedServiceTier,
         };
     }
 

src/__tests__/CodexACPAgent/CodexAcpClient.test.ts

@@ -757,6 +757,51 @@ describe('ACP server test', { timeout: 40_000 }, () => {
         });
     });
 
+    it('should fallback to the model-specific effort when reasoningEffort is unsupported', () => {
+        const result = fixture.getCodexAcpClient().createModelSelection(mockModels, '5.2-codex', 'low', null);
+        expect(result).toEqual({
+            currentModelId: "5.2-codex",
+            currentReasoningEffort: "medium",
+            currentServiceTier: null,
+        });
+    });
+
+    it('should drop stale service tier when falling back to the default model', () => {
+        const [codexModel, defaultModel] = mockModels as [Model, Model];
+        const models = [
+            {
+                ...codexModel,
+                additionalSpeedTiers: ["fast"],
+            },
+            defaultModel,
+        ];
+
+        const result = fixture.getCodexAcpClient().createModelSelection(models, 'unavailable-model', 'high', 'fast');
+        expect(result).toEqual({
+            currentModelId: "5.1",
+            currentReasoningEffort: "low",
+            currentServiceTier: null,
+        });
+    });
+
+    it('should retain service tier when selected model supports it', () => {
+        const [codexModel, defaultModel] = mockModels as [Model, Model];
+        const models = [
+            {
+                ...codexModel,
+                additionalSpeedTiers: ["fast"],
+            },
+            defaultModel,
+        ];
+
+        const result = fixture.getCodexAcpClient().createModelSelection(models, '5.2-codex', 'high', 'fast');
+        expect(result).toEqual({
+            currentModelId: "5.2-codex",
+            currentReasoningEffort: "high",
+            currentServiceTier: "fast",
+        });
+    });
+
     /**
      * Sets up a mock fixture with turnStart/awaitTurnCompleted spied on,
      * and a given session state. Returns the fixture and turnStart spy.