feat: implement experimental features system

- Add experiments.ts to manage experimental features
- Refactor experimental diff strategy into experiments system
- Add UI components for managing experimental features
- Add tests for experimental tools
- Update system prompts to handle experiments

src/core/prompts/__tests__/system.test.ts

@@ -11,6 +11,7 @@ import { defaultModeSlug, modes } from "../../../shared/modes"
 import "../../../utils/path"
 import { addCustomInstructions } from "../sections/custom-instructions"
 import * as modesSection from "../sections/modes"
+import { EXPERIMENT_IDS } from "../../../shared/experiments"
 
 // Mock the sections
 jest.mock("../sections/modes", () => ({
@@ -121,6 +122,7 @@ const createMockMcpHub = (): McpHub =>
 
 describe("SYSTEM_PROMPT", () => {
 	let mockMcpHub: McpHub
+	let experiments: Record<string, boolean>
 
 	beforeAll(() => {
 		// Ensure fs mock is properly initialized
@@ -140,6 +142,10 @@ describe("SYSTEM_PROMPT", () => {
 			"/mock/mcp/path",
 		]
 		dirs.forEach((dir) => mockFs._mockDirectories.add(dir))
+		experiments = {
+			[EXPERIMENT_IDS.SEARCH_AND_REPLACE]: false,
+			[EXPERIMENT_IDS.INSERT_BLOCK]: false,
+		}
 	})
 
 	beforeEach(() => {
@@ -164,6 +170,10 @@ describe("SYSTEM_PROMPT", () => {
 			defaultModeSlug, // mode
 			undefined, // customModePrompts
 			undefined, // customModes
+			undefined, // globalCustomInstructions
+			undefined, // preferredLanguage
+			undefined, // diffEnabled
+			experiments,
 		)
 
 		expect(prompt).toMatchSnapshot()
@@ -179,7 +189,11 @@ describe("SYSTEM_PROMPT", () => {
 			"1280x800", // browserViewportSize
 			defaultModeSlug, // mode
 			undefined, // customModePrompts
-			undefined, // customModes
+			undefined, // customModes,
+			undefined, // globalCustomInstructions
+			undefined, // preferredLanguage
+			undefined, // diffEnabled
+			experiments,
 		)
 
 		expect(prompt).toMatchSnapshot()
@@ -197,7 +211,11 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // browserViewportSize
 			defaultModeSlug, // mode
 			undefined, // customModePrompts
-			undefined, // customModes
+			undefined, // customModes,
+			undefined, // globalCustomInstructions
+			undefined, // preferredLanguage
+			undefined, // diffEnabled
+			experiments,
 		)
 
 		expect(prompt).toMatchSnapshot()
@@ -213,7 +231,11 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // browserViewportSize
 			defaultModeSlug, // mode
 			undefined, // customModePrompts
-			undefined, // customModes
+			undefined, // customModes,
+			undefined, // globalCustomInstructions
+			undefined, // preferredLanguage
+			undefined, // diffEnabled
+			experiments,
 		)
 
 		expect(prompt).toMatchSnapshot()
@@ -229,7 +251,11 @@ describe("SYSTEM_PROMPT", () => {
 			"900x600", // different viewport size
 			defaultModeSlug, // mode
 			undefined, // customModePrompts
-			undefined, // customModes
+			undefined, // customModes,
+			undefined, // globalCustomInstructions
+			undefined, // preferredLanguage
+			undefined, // diffEnabled
+			experiments,
 		)
 
 		expect(prompt).toMatchSnapshot()
@@ -249,6 +275,7 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // globalCustomInstructions
 			undefined, // preferredLanguage
 			true, // diffEnabled
+			experiments,
 		)
 
 		expect(prompt).toContain("apply_diff")
@@ -269,6 +296,7 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // globalCustomInstructions
 			undefined, // preferredLanguage
 			false, // diffEnabled
+			experiments,
 		)
 
 		expect(prompt).not.toContain("apply_diff")
@@ -289,6 +317,7 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // globalCustomInstructions
 			undefined, // preferredLanguage
 			undefined, // diffEnabled
+			experiments,
 		)
 
 		expect(prompt).not.toContain("apply_diff")
@@ -308,6 +337,8 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // customModes
 			undefined, // globalCustomInstructions
 			"Spanish", // preferredLanguage
+			undefined, // diffEnabled
+			experiments,
 		)
 
 		expect(prompt).toContain("Language Preference:")
@@ -337,6 +368,9 @@ describe("SYSTEM_PROMPT", () => {
 			undefined, // customModePrompts
 			customModes, // customModes
 			"Global instructions", // globalCustomInstructions
+			undefined, // preferredLanguage
+			undefined, // diffEnabled
+			experiments,
 		)
 
 		// Role definition should be at the top
@@ -368,6 +402,10 @@ describe("SYSTEM_PROMPT", () => {
 			defaultModeSlug,
 			customModePrompts,
 			undefined,
+			undefined,
+			undefined,
+			undefined,
+			experiments,
 		)
 
 		// Role definition from promptComponent should be at the top
@@ -394,18 +432,101 @@ describe("SYSTEM_PROMPT", () => {
 			defaultModeSlug,
 			customModePrompts,
 			undefined,
+			undefined,
+			undefined,
+			undefined,
+			experiments,
 		)
 
 		// Should use the default mode's role definition
 		expect(prompt.indexOf(modes[0].roleDefinition)).toBeLessThan(prompt.indexOf("TOOL USE"))
 	})
 
+	describe("experimental tools", () => {
+		it("should disable experimental tools by default", async () => {
+			const prompt = await SYSTEM_PROMPT(
+				mockContext,
+				"/test/path",
+				false, // supportsComputerUse
+				undefined, // mcpHub
+				undefined, // diffStrategy
+				undefined, // browserViewportSize
+				defaultModeSlug, // mode
+				undefined, // customModePrompts
+				undefined, // customModes
+				undefined, // globalCustomInstructions
+				undefined, // preferredLanguage
+				undefined, // diffEnabled
+				experiments, // experiments - undefined should disable all experimental tools
+			)
+
+			// Verify experimental tools are not included in the prompt
+			expect(prompt).not.toContain(EXPERIMENT_IDS.SEARCH_AND_REPLACE)
+			expect(prompt).not.toContain(EXPERIMENT_IDS.INSERT_BLOCK)
+		})
+
+		it("should enable experimental tools when explicitly enabled", async () => {
+			const experiments = {
+				[EXPERIMENT_IDS.SEARCH_AND_REPLACE]: true,
+				[EXPERIMENT_IDS.INSERT_BLOCK]: true,
+			}
+
+			const prompt = await SYSTEM_PROMPT(
+				mockContext,
+				"/test/path",
+				false, // supportsComputerUse
+				undefined, // mcpHub
+				undefined, // diffStrategy
+				undefined, // browserViewportSize
+				defaultModeSlug, // mode
+				undefined, // customModePrompts
+				undefined, // customModes
+				undefined, // globalCustomInstructions
+				undefined, // preferredLanguage
+				undefined, // diffEnabled
+				experiments,
+			)
+
+			// Verify experimental tools are included in the prompt when enabled
+			expect(prompt).toContain(EXPERIMENT_IDS.SEARCH_AND_REPLACE)
+			expect(prompt).toContain(EXPERIMENT_IDS.INSERT_BLOCK)
+		})
+
+		it("should selectively enable experimental tools", async () => {
+			const experiments = {
+				[EXPERIMENT_IDS.SEARCH_AND_REPLACE]: true,
+				[EXPERIMENT_IDS.INSERT_BLOCK]: false,
+			}
+
+			const prompt = await SYSTEM_PROMPT(
+				mockContext,
+				"/test/path",
+				false, // supportsComputerUse
+				undefined, // mcpHub
+				undefined, // diffStrategy
+				undefined, // browserViewportSize
+				defaultModeSlug, // mode
+				undefined, // customModePrompts
+				undefined, // customModes
+				undefined, // globalCustomInstructions
+				undefined, // preferredLanguage
+				undefined, // diffEnabled
+				experiments,
+			)
+
+			// Verify only enabled experimental tools are included
+			expect(prompt).toContain(EXPERIMENT_IDS.SEARCH_AND_REPLACE)
+			expect(prompt).not.toContain(EXPERIMENT_IDS.INSERT_BLOCK)
+		})
+	})
+
 	afterAll(() => {
 		jest.restoreAllMocks()
 	})
 })
 
 describe("addCustomInstructions", () => {
+	let experiments: Record<string, boolean>
 	beforeAll(() => {
 		// Ensure fs mock is properly initialized
 		const mockFs = jest.requireMock("fs/promises")
@@ -417,6 +538,11 @@ describe("addCustomInstructions", () => {
 			}
 			throw new Error(`ENOENT: no such file or directory, mkdir '${path}'`)
 		})
+
+		experiments = {
+			[EXPERIMENT_IDS.SEARCH_AND_REPLACE]: false,
+			[EXPERIMENT_IDS.INSERT_BLOCK]: false,
+		}
 	})
 
 	beforeEach(() => {
@@ -434,6 +560,10 @@ describe("addCustomInstructions", () => {
 			"architect", // mode
 			undefined, // customModePrompts
 			undefined, // customModes
+			undefined,
+			undefined,
+			undefined,
+			experiments,
 		)
 
 		expect(prompt).toMatchSnapshot()
@@ -450,6 +580,10 @@ describe("addCustomInstructions", () => {
 			"ask", // mode
 			undefined, // customModePrompts
 			undefined, // customModes
+			undefined,
+			undefined,
+			undefined,
+			experiments,
 		)
 
 		expect(prompt).toMatchSnapshot()

src/core/prompts/system.ts

@@ -39,6 +39,7 @@ async function generatePrompt(
 	globalCustomInstructions?: string,
 	preferredLanguage?: string,
 	diffEnabled?: boolean,
+	experiments?: Record<string, boolean>,
 ): Promise<string> {
 	if (!context) {
 		throw new Error("Extension context is required for generating system prompt")
@@ -68,6 +69,7 @@ ${getToolDescriptionsForMode(
 	browserViewportSize,
 	mcpHub,
 	customModeConfigs,
+	experiments,
 )}
 
 ${getToolUseGuidelinesSection()}
@@ -102,6 +104,7 @@ export const SYSTEM_PROMPT = async (
 	globalCustomInstructions?: string,
 	preferredLanguage?: string,
 	diffEnabled?: boolean,
+	experiments?: Record<string, boolean>,
 ): Promise<string> => {
 	if (!context) {
 		throw new Error("Extension context is required for generating system prompt")
@@ -135,5 +138,6 @@ export const SYSTEM_PROMPT = async (
 		globalCustomInstructions,
 		preferredLanguage,
 		diffEnabled,
+		experiments,
 	)
 }

src/core/prompts/tools/index.ts

@@ -46,6 +46,7 @@ export function getToolDescriptionsForMode(
 	browserViewportSize?: string,
 	mcpHub?: McpHub,
 	customModes?: ModeConfig[],
+	experiments?: Record<string, boolean>,
 ): string {
 	const config = getModeConfig(mode, customModes)
 	const args: ToolArgs = {
@@ -64,7 +65,7 @@ export function getToolDescriptionsForMode(
 		const toolGroup = TOOL_GROUPS[groupName]
 		if (toolGroup) {
 			toolGroup.forEach((tool) => {
-				if (isToolAllowedForMode(tool as ToolName, mode, customModes ?? [])) {
+				if (isToolAllowedForMode(tool as ToolName, mode, customModes ?? [], experiments ?? {})) {
 					tools.add(tool)
 				}
 			})