fix: allow variant override even with agent model config (#3163)

model-selection.ts now separates model selection from variant/reasoning
tier, so agent model overrides don't lock the variant.

34 tests pass, 5009 total, tsc clean.

Closes #3163

src/tools/delegate-task/category-resolver.test.ts

@@ -197,7 +197,7 @@ describe("resolveCategoryExecution", () => {
 		if (!result.actualModel || !result.categoryModel) {
 			throw new Error("Expected resolved model and category model")
 		}
-		expect(result.actualModel).toBe("openai/gpt-5.4 high")
+		expect(result.actualModel).toBe("openai/gpt-5.4")
 		expect(result.categoryModel).toEqual({
 			providerID: "openai",
 			modelID: "gpt-5.4",

src/tools/delegate-task/model-selection.test.ts

@@ -254,6 +254,100 @@ describe("resolveModelForDelegateTask", () => {
 		})
 	})
 
+	describe("#given user model override includes variant syntax", () => {
+		describe("#when userModel contains space-separated variant", () => {
+			test("#then extracts the variant and returns the base model separately", () => {
+				const result = resolveModelForDelegateTask({
+					userModel: "openai/gpt-5.4 high",
+					categoryDefaultModel: "anthropic/claude-sonnet-4-6",
+					fallbackChain: [
+						{ providers: ["anthropic"], model: "claude-sonnet-4-6" },
+					],
+					availableModels: new Set(["openai/gpt-5.4"]),
+				})
+
+				expect(result).toEqual({ model: "openai/gpt-5.4", variant: "high" })
+			})
+		})
+
+		describe("#when userModel contains parenthesized variant", () => {
+			test("#then extracts the variant and returns the base model separately", () => {
+				const result = resolveModelForDelegateTask({
+					userModel: "openai/gpt-5.4(max)",
+					categoryDefaultModel: "anthropic/claude-sonnet-4-6",
+					availableModels: new Set(),
+				})
+
+				expect(result).toEqual({ model: "openai/gpt-5.4", variant: "max" })
+			})
+		})
+
+		describe("#when userModel has no variant syntax", () => {
+			test("#then returns the model without a variant (backward compat)", () => {
+				const result = resolveModelForDelegateTask({
+					userModel: "openai/gpt-5.4",
+					availableModels: new Set(),
+				})
+
+				expect(result).toEqual({ model: "openai/gpt-5.4" })
+			})
+		})
+
+		describe("#when userModel has a non-variant suffix (e.g. -high in model name)", () => {
+			test("#then preserves the full model name without extracting a variant", () => {
+				const result = resolveModelForDelegateTask({
+					userModel: "new-api-openai/gpt-5.4-high",
+					availableModels: new Set(),
+				})
+
+				expect(result).toEqual({ model: "new-api-openai/gpt-5.4-high" })
+			})
+		})
+	})
+
+	describe("#given user-configured category model includes variant syntax", () => {
+		beforeEach(() => {
+			hasConnectedProvidersSpy = spyOn(connectedProvidersCache, "hasConnectedProvidersCache").mockReturnValue(true)
+			hasProviderModelsSpy = spyOn(connectedProvidersCache, "hasProviderModelsCache").mockReturnValue(true)
+		})
+
+		describe("#when categoryDefaultModel with isUserConfiguredCategoryModel contains a space-separated variant", () => {
+			test("#then extracts the variant and returns the base model separately", () => {
+				const result = resolveModelForDelegateTask({
+					categoryDefaultModel: "openai/gpt-5.4 medium",
+					isUserConfiguredCategoryModel: true,
+					availableModels: new Set(["openai/gpt-5.4"]),
+				})
+
+				expect(result).toEqual({ model: "openai/gpt-5.4", variant: "medium" })
+			})
+		})
+
+		describe("#when categoryDefaultModel with isUserConfiguredCategoryModel contains a parenthesized variant", () => {
+			test("#then extracts the variant and returns the base model separately", () => {
+				const result = resolveModelForDelegateTask({
+					categoryDefaultModel: "openai/gpt-5.4(xhigh)",
+					isUserConfiguredCategoryModel: true,
+					availableModels: new Set(),
+				})
+
+				expect(result).toEqual({ model: "openai/gpt-5.4", variant: "xhigh" })
+			})
+		})
+
+		describe("#when categoryDefaultModel with isUserConfiguredCategoryModel has no variant", () => {
+			test("#then returns the model without a variant (backward compat)", () => {
+				const result = resolveModelForDelegateTask({
+					categoryDefaultModel: "new-api-openai/gpt-5.4-high",
+					isUserConfiguredCategoryModel: true,
+					availableModels: new Set(["openai/gpt-5.4"]),
+				})
+
+				expect(result).toEqual({ model: "new-api-openai/gpt-5.4-high" })
+			})
+		})
+	})
+
 	describe("#given only connected providers cache exists (no provider-models cache)", () => {
 		beforeEach(() => {
 			hasConnectedProvidersSpy = spyOn(connectedProvidersCache, "hasConnectedProvidersCache").mockReturnValue(true)

src/tools/delegate-task/model-selection.ts

@@ -56,6 +56,10 @@ export function resolveModelForDelegateTask(input: {
 }): { model: string; variant?: string; fallbackEntry?: FallbackEntry; matchedFallback?: boolean } | { skipped: true } | undefined {
   const userModel = normalizeModel(input.userModel)
   if (userModel) {
+    const parsed = parseUserFallbackModel(userModel)
+    if (parsed?.variant) {
+      return { model: parsed.baseModel, variant: parsed.variant }
+    }
     return { model: userModel }
   }
 
@@ -75,6 +79,10 @@ export function resolveModelForDelegateTask(input: {
       log("[resolveModelForDelegateTask] using user-configured category model (bypass validation)", {
         categoryDefaultModel: categoryDefault,
       })
+      const parsed = parseUserFallbackModel(categoryDefault)
+      if (parsed?.variant) {
+        return { model: parsed.baseModel, variant: parsed.variant }
+      }
       return { model: categoryDefault }
     }