fix: pass through custom model names in Gemini provider instead of falling back to default

src/api/providers/__tests__/gemini.spec.ts

@@ -165,13 +165,25 @@ describe("GeminiHandler", () => {
 			expect(modelInfo.info).toBeDefined()
 		})
 
-		it("should return default model if invalid model specified", () => {
-			const invalidHandler = new GeminiHandler({
-				apiModelId: "invalid-model",
+		it("should pass through custom model names not in the predefined list", () => {
+			const customHandler = new GeminiHandler({
+				apiModelId: "gemini-3.1-flash-lite-preview",
 				geminiApiKey: "test-key",
 			})
-			const modelInfo = invalidHandler.getModel()
-			expect(modelInfo.id).toBe(geminiDefaultModelId) // Default model
+			const modelInfo = customHandler.getModel()
+			expect(modelInfo.id).toBe("gemini-3.1-flash-lite-preview")
+			expect(modelInfo.info).toBeDefined()
+			expect(modelInfo.info.maxTokens).toBe(8192)
+			expect(modelInfo.info.supportsImages).toBe(true)
+		})
+
+		it("should return default model when no model ID is specified", () => {
+			const noModelHandler = new GeminiHandler({
+				apiModelId: undefined as any,
+				geminiApiKey: "test-key",
+			})
+			const modelInfo = noModelHandler.getModel()
+			expect(modelInfo.id).toBe(geminiDefaultModelId)
 		})
 
 		it("should exclude apply_diff and include edit in tool preferences", () => {

src/api/providers/gemini.ts

@@ -348,8 +348,29 @@ export class GeminiHandler extends BaseProvider implements SingleCompletionHandl
 
 	override getModel() {
 		const modelId = this.options.apiModelId
-		let id = modelId && modelId in geminiModels ? (modelId as GeminiModelId) : geminiDefaultModelId
-		let info: ModelInfo = geminiModels[id]
+
+		let id: string
+		let info: ModelInfo
+
+		if (modelId && modelId in geminiModels) {
+			// Known Gemini model -- use its curated ModelInfo.
+			id = modelId as GeminiModelId
+			info = geminiModels[id as GeminiModelId]
+		} else if (modelId) {
+			// Custom model name not in the predefined list.
+			// Pass it through as-is so the user's chosen model is respected.
+			id = modelId
+			info = {
+				maxTokens: 8192,
+				contextWindow: 1_048_576,
+				supportsImages: true,
+				supportsPromptCache: false,
+			}
+		} else {
+			// No model specified -- fall back to the default.
+			id = geminiDefaultModelId
+			info = geminiModels[geminiDefaultModelId]
+		}
 
 		const params = getModelParams({
 			format: "gemini",