fix: disable Gemini grounding for code generation to prevent array index removal

When Gemini grounding is enabled, it misinterprets array indices like [0] as citation markers and removes them from generated code. This fix detects code generation contexts and temporarily disables grounding to preserve array indices.

Fixes #8914

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

@@ -164,6 +164,145 @@ describe("GeminiHandler", () => {
 		})
 	})
 
+	describe("grounding bypass for code generation", () => {
+		it("should disable grounding when code generation context is detected", async () => {
+			const codeHandler = new GeminiHandler({
+				apiModelId: GEMINI_20_FLASH_THINKING_NAME,
+				geminiApiKey: "test-key",
+				enableGrounding: true, // Grounding is enabled
+			})
+
+			// Mock the client's generateContentStream method
+			const mockGenerateContentStream = vi.fn().mockResolvedValue({
+				[Symbol.asyncIterator]: async function* () {
+					yield {
+						text: "fruits = ['apple', 'banana']\nmyfruit = fruits[0]",
+						usageMetadata: { promptTokenCount: 100, candidatesTokenCount: 50 },
+					}
+				},
+			})
+			codeHandler["client"].models.generateContentStream = mockGenerateContentStream
+
+			// Test message that includes code generation request
+			const messages: Anthropic.Messages.MessageParam[] = [
+				{
+					role: "user",
+					content: [
+						{
+							type: "text",
+							text: "Create a python file that creates a list of 10 fruits and put the first one in the variable 'myfruit'",
+						},
+					],
+				},
+			]
+
+			const stream = codeHandler.createMessage("System prompt", messages)
+			const chunks = []
+			for await (const chunk of stream) {
+				chunks.push(chunk)
+			}
+
+			// Verify that googleSearch was NOT added to tools (grounding disabled)
+			const callArgs = mockGenerateContentStream.mock.calls[0][0]
+			const tools = callArgs.config.tools || []
+			const hasGrounding = tools.some((tool: any) => "googleSearch" in tool)
+			expect(hasGrounding).toBe(false)
+		})
+
+		it("should enable grounding for non-code contexts when enableGrounding is true", async () => {
+			const nonCodeHandler = new GeminiHandler({
+				apiModelId: GEMINI_20_FLASH_THINKING_NAME,
+				geminiApiKey: "test-key",
+				enableGrounding: true,
+			})
+
+			// Mock the client's generateContentStream method
+			const mockGenerateContentStream = vi.fn().mockResolvedValue({
+				[Symbol.asyncIterator]: async function* () {
+					yield {
+						text: "The weather today is sunny.",
+						usageMetadata: { promptTokenCount: 100, candidatesTokenCount: 50 },
+					}
+				},
+			})
+			nonCodeHandler["client"].models.generateContentStream = mockGenerateContentStream
+
+			// Test message without code generation context
+			const messages: Anthropic.Messages.MessageParam[] = [
+				{
+					role: "user",
+					content: [
+						{
+							type: "text",
+							text: "What's the weather like today?",
+						},
+					],
+				},
+			]
+
+			const stream = nonCodeHandler.createMessage("System prompt", messages)
+			const chunks = []
+			for await (const chunk of stream) {
+				chunks.push(chunk)
+			}
+
+			// Verify that googleSearch WAS added to tools (grounding enabled)
+			const callArgs = mockGenerateContentStream.mock.calls[0][0]
+			const tools = callArgs.config.tools || []
+			const hasGrounding = tools.some((tool: any) => "googleSearch" in tool)
+			expect(hasGrounding).toBe(true)
+		})
+
+		it("should correctly identify various code generation patterns", async () => {
+			const handler = new GeminiHandler({
+				apiModelId: GEMINI_20_FLASH_THINKING_NAME,
+				geminiApiKey: "test-key",
+			})
+
+			// Test various code generation patterns
+			const codePatterns = [
+				"Create a python file with a list",
+				"Write a javascript function",
+				"Generate code snippet",
+				"Implement a class method",
+				"def my_function():",
+				"function getData() {",
+				"fruits[0] = 'apple'",
+				"array[5]",
+			]
+
+			for (const pattern of codePatterns) {
+				const messages: Anthropic.Messages.MessageParam[] = [
+					{
+						role: "user",
+						content: [{ type: "text", text: pattern }],
+					},
+				]
+				const result = handler["isCodeGenerationContext"](messages)
+				expect(result).toBe(true)
+			}
+
+			// Test non-code patterns
+			const nonCodePatterns = [
+				"What's the weather?",
+				"Explain quantum physics",
+				"Tell me a story",
+				"How do I cook pasta?",
+			]
+
+			for (const pattern of nonCodePatterns) {
+				const messages: Anthropic.Messages.MessageParam[] = [
+					{
+						role: "user",
+						content: [{ type: "text", text: pattern }],
+					},
+				]
+				const result = handler["isCodeGenerationContext"](messages)
+				expect(result).toBe(false)
+			}
+		})
+	})
+
 	describe("calculateCost", () => {
 		// Mock ModelInfo based on gemini-1.5-flash-latest pricing (per 1M tokens)
 		// Removed 'id' and 'name' as they are not part of ModelInfo type directly

src/api/providers/gemini.ts

@@ -60,6 +60,52 @@ export class GeminiHandler extends BaseProvider implements SingleCompletionHandl
 					: new GoogleGenAI({ apiKey })
 	}
 
+	/**
+	 * Detects if the conversation context suggests code generation.
+	 * This helps prevent Gemini's grounding feature from incorrectly
+	 * removing array indices like [0] which it may interpret as citations.
+	 */
+	private isCodeGenerationContext(messages: Anthropic.Messages.MessageParam[]): boolean {
+		// Keywords that strongly suggest code generation
+		const codeKeywords = [
+			"create.*(?:file|script|function|class|method|code|program)",
+			"write.*(?:file|script|function|class|method|code|program)",
+			"generate.*(?:file|script|function|class|method|code|program)",
+			"implement.*(?:function|class|method|algorithm)",
+			"python file",
+			"javascript file",
+			"typescript file",
+			"code snippet",
+			"code example",
+			"def\\s+\\w+\\s*\\(", // Python function definition
+			"function\\s+\\w+\\s*\\(", // JavaScript function
+			"class\\s+\\w+", // Class definition
+			"\\[\\d+\\]", // Array index patterns
+			"array\\[",
+			"list\\[",
+			"fruits\\[0\\]", // Specific to the reported issue
+		]
+
+		const codePattern = new RegExp(codeKeywords.join("|"), "i")
+
+		// Check recent messages for code-related content
+		const recentMessages = messages.slice(-5) // Check last 5 messages
+
+		for (const message of recentMessages) {
+			if (Array.isArray(message.content)) {
+				for (const block of message.content) {
+					if (block.type === "text" && codePattern.test(block.text)) {
+						return true
+					}
+				}
+			} else if (typeof message.content === "string" && codePattern.test(message.content)) {
+				return true
+			}
+		}
+
+		return false
+	}
+
 	async *createMessage(
 		systemInstruction: string,
 		messages: Anthropic.Messages.MessageParam[],
@@ -74,7 +120,10 @@ export class GeminiHandler extends BaseProvider implements SingleCompletionHandl
 			tools.push({ urlContext: {} })
 		}
 
-		if (this.options.enableGrounding) {
+		// Only enable grounding if it's not a code generation context
+		// This prevents Gemini from misinterpreting array indices like [0] as citation markers
+		const isCodeContext = this.isCodeGenerationContext(messages)
+		if (this.options.enableGrounding && !isCodeContext) {
 			tools.push({ googleSearch: {} })
 		}
 
@@ -217,7 +266,13 @@ export class GeminiHandler extends BaseProvider implements SingleCompletionHandl
 			if (this.options.enableUrlContext) {
 				tools.push({ urlContext: {} })
 			}
-			if (this.options.enableGrounding) {
+
+			// Check if the prompt suggests code generation
+			const isCodeContext = this.isCodeGenerationContext([
+				{ role: "user", content: [{ type: "text", text: prompt }] },
+			])
+
+			if (this.options.enableGrounding && !isCodeContext) {
 				tools.push({ googleSearch: {} })
 			}
 			const promptConfig: GenerateContentConfig = {