feat: gate unified user message tag behind experimental setting

- Add UNIFIED_USER_MESSAGE_TAG experiment (disabled by default)
- Create userContentTags utility for conditional tag formatting
- Update Task.ts to conditionally wrap task/resume content
- Update tool files (AskFollowupQuestion, AttemptCompletion, ExecuteCommand) to conditionally wrap feedback/answers
- Update formatResponse functions to accept useUnifiedTag parameter
- Update presentAssistantMessage.ts to pass experiment flag
- Update ReadFileTool.ts to pass experiment flag
- Update processUserContentMentions.ts to detect tags based on experiment

When experiment is disabled (default):
- Uses legacy tags: <task>, <feedback>, <answer>
- Maintains backward compatibility

When experiment is enabled:
- Uses unified <user_message> tag for all contexts
- Simplifies tag detection and handling

Relates to COM-450

packages/types/src/experiment.ts

@@ -14,6 +14,7 @@ export const experimentIds = [
 	"runSlashCommand",
 	"multipleNativeToolCalls",
 	"customTools",
+	"unifiedUserMessageTag",
 ] as const
 
 export const experimentIdsSchema = z.enum(experimentIds)
@@ -32,6 +33,7 @@ export const experimentsSchema = z.object({
 	runSlashCommand: z.boolean().optional(),
 	multipleNativeToolCalls: z.boolean().optional(),
 	customTools: z.boolean().optional(),
+	unifiedUserMessageTag: z.boolean().optional(),
 })
 
 export type Experiments = z.infer<typeof experimentsSchema>

src/core/assistant-message/presentAssistantMessage.ts

@@ -73,6 +73,10 @@ export async function presentAssistantMessage(cline: Task) {
 	cline.presentAssistantMessageLocked = true
 	cline.presentAssistantMessageHasPendingUpdates = false
 
+	// Get experiment setting for unified tags once for this presentation
+	const state = await cline.providerRef.deref()?.getState()
+	const useUnifiedTag = experiments.isEnabled(state?.experiments ?? {}, EXPERIMENT_IDS.UNIFIED_USER_MESSAGE_TAG)
+
 	if (cline.currentStreamingContentIndex >= cline.assistantMessageContent.length) {
 		// This may happen if the last content block was completed before
 		// streaming could finish. If streaming is finished, and we're out of
@@ -174,7 +178,7 @@ export async function presentAssistantMessage(cline: Task) {
 
 				// Merge approval feedback into tool result (GitHub #10465)
 				if (approvalFeedback) {
-					const feedbackText = formatResponse.toolApprovedWithFeedback(approvalFeedback.text, toolProtocol)
+					const feedbackText = formatResponse.toolApprovedWithFeedback(approvalFeedback.text, toolProtocol, useUnifiedTag)
 					resultContent = `${feedbackText}\n\n${resultContent}`
 
 					// Add feedback images to the image blocks
@@ -221,7 +225,7 @@ export async function presentAssistantMessage(cline: Task) {
 						await cline.say("user_feedback", text, images)
 						pushToolResult(
 							formatResponse.toolResult(
-								formatResponse.toolDeniedWithFeedback(text, toolProtocol),
+								formatResponse.toolDeniedWithFeedback(text, toolProtocol, useUnifiedTag),
 								images,
 							),
 						)
@@ -372,8 +376,7 @@ export async function presentAssistantMessage(cline: Task) {
 			break
 		}
 		case "tool_use": {
-			// Fetch state early so it's available for toolDescription and validation
-			const state = await cline.providerRef.deref()?.getState()
+			// Use already-fetched state for toolDescription and validation
 			const { mode, customModes, experiments: stateExperiments } = state ?? {}
 
 			const toolDescription = (): string => {
@@ -556,6 +559,7 @@ export async function presentAssistantMessage(cline: Task) {
 						const feedbackText = formatResponse.toolApprovedWithFeedback(
 							approvalFeedback.text,
 							toolProtocol,
+							useUnifiedTag,
 						)
 						resultContent = `${feedbackText}\n\n${resultContent}`
 
@@ -597,6 +601,7 @@ export async function presentAssistantMessage(cline: Task) {
 						const feedbackText = formatResponse.toolApprovedWithFeedback(
 							approvalFeedback.text,
 							toolProtocol,
+							useUnifiedTag,
 						)
 						resultContent = `${feedbackText}\n\n${resultContent}`
 					}
@@ -658,7 +663,7 @@ export async function presentAssistantMessage(cline: Task) {
 						await cline.say("user_feedback", text, images)
 						pushToolResult(
 							formatResponse.toolResult(
-								formatResponse.toolDeniedWithFeedback(text, toolProtocol),
+								formatResponse.toolDeniedWithFeedback(text, toolProtocol, useUnifiedTag),
 								images,
 							),
 						)

src/core/mentions/processUserContentMentions.ts

@@ -2,6 +2,7 @@ import { Anthropic } from "@anthropic-ai/sdk"
 import { parseMentions, ParseMentionsResult } from "./index"
 import { UrlContentFetcher } from "../../services/browser/UrlContentFetcher"
 import { FileContextTracker } from "../context-tracking/FileContextTracker"
+import { hasUserContentTags } from "../../utils/userContentTags"
 
 export interface ProcessUserContentMentionsResult {
 	content: Anthropic.Messages.ContentBlockParam[]
@@ -9,7 +10,7 @@ export interface ProcessUserContentMentionsResult {
 }
 
 /**
- * Process mentions in user content, specifically within task and feedback tags
+ * Process mentions in user content, specifically within user message tags
  */
 export async function processUserContentMentions({
 	userContent,
@@ -21,6 +22,7 @@ export async function processUserContentMentions({
 	includeDiagnosticMessages = true,
 	maxDiagnosticMessages = 50,
 	maxReadFileLine,
+	useUnifiedTag = false,
 }: {
 	userContent: Anthropic.Messages.ContentBlockParam[]
 	cwd: string
@@ -31,6 +33,7 @@ export async function processUserContentMentions({
 	includeDiagnosticMessages?: boolean
 	maxDiagnosticMessages?: number
 	maxReadFileLine?: number
+	useUnifiedTag?: boolean
 }): Promise<ProcessUserContentMentionsResult> {
 	// Track the first mode found from slash commands
 	let commandMode: string | undefined
@@ -38,20 +41,13 @@ export async function processUserContentMentions({
 	// Process userContent array, which contains various block types:
 	// TextBlockParam, ImageBlockParam, ToolUseBlockParam, and ToolResultBlockParam.
 	// We need to apply parseMentions() to:
-	// 1. All TextBlockParam's text (first user message with task)
-	// 2. ToolResultBlockParam's content/context text arrays if it contains
-	// "<feedback>" (see formatToolDeniedFeedback, attemptCompletion,
-	// executeCommand, and consecutiveMistakeCount >= 3) or "<answer>"
-	// (see askFollowupQuestion), we place all user generated content in
-	// these tags so they can effectively be used as markers for when we
-	// should parse mentions).
+	// 1. All TextBlockParam's text (first user message)
+	// 2. ToolResultBlockParam's content/context text arrays if it contains user content tags
+	// We place all user generated content in these tags so they can effectively be used as
+	// markers for when we should parse mentions.
 	const content = await Promise.all(
 		userContent.map(async (block) => {
-			const shouldProcessMentions = (text: string) =>
-				text.includes("<task>") ||
-				text.includes("<feedback>") ||
-				text.includes("<answer>") ||
-				text.includes("<user_message>")
+			const shouldProcessMentions = (text: string) => hasUserContentTags(text, useUnifiedTag)
 
 			if (block.type === "text") {
 				if (shouldProcessMentions(block.text)) {

src/core/prompts/responses.ts

@@ -4,6 +4,7 @@ import * as diff from "diff"
 import { RooIgnoreController, LOCK_TEXT_SYMBOL } from "../ignore/RooIgnoreController"
 import { RooProtectedController } from "../protect/RooProtectedController"
 import { ToolProtocol, isNativeProtocol, TOOL_PROTOCOL } from "@roo-code/types"
+import { wrapUserContent } from "../../utils/userContentTags"
 
 export const formatResponse = {
 	toolDenied: (protocol?: ToolProtocol) => {
@@ -16,26 +17,26 @@ export const formatResponse = {
 		return `The user denied this operation.`
 	},
 
-	toolDeniedWithFeedback: (feedback?: string, protocol?: ToolProtocol) => {
+	toolDeniedWithFeedback: (feedback?: string, protocol?: ToolProtocol, useUnifiedTag?: boolean) => {
 		if (isNativeProtocol(protocol ?? TOOL_PROTOCOL.XML)) {
 			return JSON.stringify({
 				status: "denied",
-				message: "The user denied this operation and provided the following feedback",
 				feedback: feedback,
 			})
 		}
-		return `The user denied this operation and provided the following feedback:\n<feedback>\n${feedback}\n</feedback>`
+		const wrappedFeedback = wrapUserContent(feedback ?? "", "feedback", useUnifiedTag ?? false)
+		return `The user denied this operation and responded with the message:\n${wrappedFeedback}`
 	},
 
-	toolApprovedWithFeedback: (feedback?: string, protocol?: ToolProtocol) => {
+	toolApprovedWithFeedback: (feedback?: string, protocol?: ToolProtocol, useUnifiedTag?: boolean) => {
 		if (isNativeProtocol(protocol ?? TOOL_PROTOCOL.XML)) {
 			return JSON.stringify({
 				status: "approved",
-				message: "The user approved this operation and provided the following context",
 				feedback: feedback,
 			})
 		}
-		return `The user approved this operation and provided the following context:\n<feedback>\n${feedback}\n</feedback>`
+		const wrappedFeedback = wrapUserContent(feedback ?? "", "feedback", useUnifiedTag ?? false)
+		return `The user approved this operation and responded with the message:\n${wrappedFeedback}`
 	},
 
 	toolError: (error?: string, protocol?: ToolProtocol) => {
@@ -77,15 +78,15 @@ Otherwise, if you have not completed the task and do not need additional informa
 (This is an automated message, so do not respond to it conversationally.)`
 	},
 
-	tooManyMistakes: (feedback?: string, protocol?: ToolProtocol) => {
+	tooManyMistakes: (feedback?: string, protocol?: ToolProtocol, useUnifiedTag?: boolean) => {
 		if (isNativeProtocol(protocol ?? TOOL_PROTOCOL.XML)) {
 			return JSON.stringify({
 				status: "guidance",
-				message: "You seem to be having trouble proceeding",
 				feedback: feedback,
 			})
 		}
-		return `You seem to be having trouble proceeding. The user has provided the following feedback to help guide you:\n<feedback>\n${feedback}\n</feedback>`
+		const wrappedFeedback = wrapUserContent(feedback ?? "", "feedback", useUnifiedTag ?? false)
+		return `You seem to be having trouble proceeding. The user has provided the following feedback to help guide you:\n${wrappedFeedback}`
 	},
 
 	missingToolParameterError: (paramName: string, protocol?: ToolProtocol) => {

src/core/task/Task.ts

@@ -73,6 +73,7 @@ import { defaultModeSlug, getModeBySlug, getGroupName } from "../../shared/modes
 import { DiffStrategy, type ToolUse, type ToolParamName, toolParamNames } from "../../shared/tools"
 import { EXPERIMENT_IDS, experiments } from "../../shared/experiments"
 import { getModelMaxOutputTokens } from "../../shared/api"
+import { wrapUserContent } from "../../utils/userContentTags"
 
 // services
 import { UrlContentFetcher } from "../../services/browser/UrlContentFetcher"
@@ -2508,9 +2509,13 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 				)
 
 				if (response === "messageResponse") {
+					// Get experiment setting for unified tags
+					const mistakeState = await this.providerRef.deref()?.getState()
+					const useUnifiedTagForMistakes = experiments.isEnabled(mistakeState?.experiments ?? {}, EXPERIMENT_IDS.UNIFIED_USER_MESSAGE_TAG)
+
 					currentUserContent.push(
 						...[
-							{ type: "text" as const, text: formatResponse.tooManyMistakes(text) },
+							{ type: "text" as const, text: formatResponse.tooManyMistakes(text, this._taskToolProtocol, useUnifiedTagForMistakes) },
 							...formatResponse.imageBlocks(images),
 						],
 					)
@@ -2553,8 +2558,11 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 				includeDiagnosticMessages = true,
 				maxDiagnosticMessages = 50,
 				maxReadFileLine = -1,
+				experiments: experimentsConfig,
 			} = (await this.providerRef.deref()?.getState()) ?? {}
 
+			const useUnifiedTag = experiments.isEnabled(experimentsConfig ?? {}, EXPERIMENT_IDS.UNIFIED_USER_MESSAGE_TAG)
+
 			const { content: parsedUserContent, mode: slashCommandMode } = await processUserContentMentions({
 				userContent: currentUserContent,
 				cwd: this.cwd,
@@ -2565,6 +2573,7 @@ export class Task extends EventEmitter<TaskEvents> implements TaskLike {
 				includeDiagnosticMessages,
 				maxDiagnosticMessages,
 				maxReadFileLine,
+				useUnifiedTag,
 			})
 
 			// Switch mode if specified in a slash command's frontmatter

src/core/tools/AskFollowupQuestionTool.ts

@@ -2,6 +2,8 @@ import { Task } from "../task/Task"
 import { formatResponse } from "../prompts/responses"
 import { parseXml } from "../../utils/xml"
 import type { ToolUse } from "../../shared/tools"
+import { wrapUserContent } from "../../utils/userContentTags"
+import { experiments, EXPERIMENT_IDS } from "../../shared/experiments"
 
 import { BaseTool, ToolCallbacks } from "./BaseTool"
 
@@ -86,7 +88,13 @@ export class AskFollowupQuestionTool extends BaseTool<"ask_followup_question"> {
 			task.consecutiveMistakeCount = 0
 			const { text, images } = await task.ask("followup", JSON.stringify(follow_up_json), false)
 			await task.say("user_feedback", text ?? "", images)
-			pushToolResult(formatResponse.toolResult(`<answer>\n${text}\n</answer>`, images))
+
+			// Get experiment setting for unified tags
+			const state = await task.providerRef.deref()?.getState()
+			const useUnifiedTag = experiments.isEnabled(state?.experiments ?? {}, EXPERIMENT_IDS.UNIFIED_USER_MESSAGE_TAG)
+			const wrappedAnswer = wrapUserContent(text ?? "", "answer", useUnifiedTag)
+
+			pushToolResult(formatResponse.toolResult(wrappedAnswer, images))
 		} catch (error) {
 			await handleError("asking question", error as Error)
 		}

src/core/tools/AttemptCompletionTool.ts

@@ -8,6 +8,8 @@ import { formatResponse } from "../prompts/responses"
 import { Package } from "../../shared/package"
 import type { ToolUse } from "../../shared/tools"
 import { t } from "../../i18n"
+import { wrapUserContent } from "../../utils/userContentTags"
+import { experiments, EXPERIMENT_IDS } from "../../shared/experiments"
 
 import { BaseTool, ToolCallbacks } from "./BaseTool"
 
@@ -150,8 +152,12 @@ export class AttemptCompletionTool extends BaseTool<"attempt_completion"> {
 			// User provided feedback - push tool result to continue the conversation
 			await task.say("user_feedback", text ?? "", images)
 
-			const feedbackText = `The user has provided feedback on the results. Consider their input to continue the task, and then attempt completion again.\n<feedback>\n${text}\n</feedback>`
-			pushToolResult(formatResponse.toolResult(feedbackText, images))
+			// Get experiment setting for unified tags
+			const state = await task.providerRef.deref()?.getState()
+			const useUnifiedTag = experiments.isEnabled(state?.experiments ?? {}, EXPERIMENT_IDS.UNIFIED_USER_MESSAGE_TAG)
+			const wrappedFeedback = wrapUserContent(text ?? "", "feedback", useUnifiedTag)
+
+			pushToolResult(formatResponse.toolResult(wrappedFeedback, images))
 		} catch (error) {
 			await handleError("inspecting site", error as Error)
 		}

src/core/tools/ExecuteCommandTool.ts

@@ -18,6 +18,8 @@ import { Terminal } from "../../integrations/terminal/Terminal"
 import { Package } from "../../shared/package"
 import { t } from "../../i18n"
 import { BaseTool, ToolCallbacks } from "./BaseTool"
+import { wrapUserContent } from "../../utils/userContentTags"
+import { experiments, EXPERIMENT_IDS } from "../../shared/experiments"
 
 class ShellIntegrationError extends Error {}
 
@@ -334,14 +336,18 @@ export async function executeCommandInTerminal(
 		const { text, images } = message
 		await task.say("user_feedback", text, images)
 
+		// Get experiment setting for unified tags
+		const state = await task.providerRef.deref()?.getState()
+		const useUnifiedTag = experiments.isEnabled(state?.experiments ?? {}, EXPERIMENT_IDS.UNIFIED_USER_MESSAGE_TAG)
+		const wrappedFeedback = wrapUserContent(text ?? "", "feedback", useUnifiedTag)
+
 		return [
 			true,
 			formatResponse.toolResult(
 				[
 					`Command is still running in terminal from '${terminal.getCurrentWorkingDirectory().toPosix()}'.`,
 					result.length > 0 ? `Here's the output so far:\n${result}\n` : "\n",
-					`The user provided the following feedback:`,
-					`<feedback>\n${text}\n</feedback>`,
+					wrappedFeedback,
 				].join("\n"),
 				images,
 			),

src/core/tools/ReadFileTool.ts

@@ -19,6 +19,7 @@ import { parseSourceCodeDefinitionsForFile } from "../../services/tree-sitter"
 import { parseXml } from "../../utils/xml"
 import { resolveToolProtocol } from "../../utils/resolveToolProtocol"
 import type { ToolUse } from "../../shared/tools"
+import { experiments, EXPERIMENT_IDS } from "../../shared/experiments"
 
 import {
 	DEFAULT_MAX_IMAGE_FILE_SIZE_MB,
@@ -343,7 +344,9 @@ export class ReadFileTool extends BaseTool<"read_file"> {
 				maxReadFileLine = -1,
 				maxImageFileSize = DEFAULT_MAX_IMAGE_FILE_SIZE_MB,
 				maxTotalImageSize = DEFAULT_MAX_TOTAL_IMAGE_SIZE_MB,
+				experiments: stateExperiments,
 			} = state ?? {}
+			const useUnifiedTag = experiments.isEnabled(stateExperiments ?? {}, EXPERIMENT_IDS.UNIFIED_USER_MESSAGE_TAG)
 
 			for (const fileResult of fileResults) {
 				if (fileResult.status !== "approved") continue
@@ -649,17 +652,17 @@ export class ReadFileTool extends BaseTool<"read_file"> {
 			const deniedWithFeedback = fileResults.find((result) => result.status === "denied" && result.feedbackText)
 
 			if (deniedWithFeedback && deniedWithFeedback.feedbackText) {
-				statusMessage = formatResponse.toolDeniedWithFeedback(deniedWithFeedback.feedbackText)
+				statusMessage = formatResponse.toolDeniedWithFeedback(deniedWithFeedback.feedbackText, toolProtocol, useUnifiedTag)
 				feedbackImages = deniedWithFeedback.feedbackImages || []
 			} else if (task.didRejectTool) {
-				statusMessage = formatResponse.toolDenied()
+				statusMessage = formatResponse.toolDenied(toolProtocol)
 			} else {
 				const approvedWithFeedback = fileResults.find(
 					(result) => result.status === "approved" && result.feedbackText,
 				)
 
 				if (approvedWithFeedback && approvedWithFeedback.feedbackText) {
-					statusMessage = formatResponse.toolApprovedWithFeedback(approvedWithFeedback.feedbackText)
+					statusMessage = formatResponse.toolApprovedWithFeedback(approvedWithFeedback.feedbackText, toolProtocol, useUnifiedTag)
 					feedbackImages = approvedWithFeedback.feedbackImages || []
 				}
 			}

src/shared/experiments.ts

@@ -8,6 +8,7 @@ export const EXPERIMENT_IDS = {
 	RUN_SLASH_COMMAND: "runSlashCommand",
 	MULTIPLE_NATIVE_TOOL_CALLS: "multipleNativeToolCalls",
 	CUSTOM_TOOLS: "customTools",
+	UNIFIED_USER_MESSAGE_TAG: "unifiedUserMessageTag",
 } as const satisfies Record<string, ExperimentId>
 
 type _AssertExperimentIds = AssertEqual<Equals<ExperimentId, Values<typeof EXPERIMENT_IDS>>>
@@ -26,6 +27,7 @@ export const experimentConfigsMap: Record<ExperimentKey, ExperimentConfig> = {
 	RUN_SLASH_COMMAND: { enabled: false },
 	MULTIPLE_NATIVE_TOOL_CALLS: { enabled: false },
 	CUSTOM_TOOLS: { enabled: false },
+	UNIFIED_USER_MESSAGE_TAG: { enabled: false },
 }
 
 export const experimentDefault = Object.fromEntries(

src/utils/userContentTags.ts

@@ -0,0 +1,82 @@
+/**
+ * Utilities for handling user content wrapper tags.
+ * 
+ * When the UNIFIED_USER_MESSAGE_TAG experiment is enabled, all user content
+ * (task start, feedback, answers, resume messages) uses a single <user_message> tag.
+ * 
+ * When disabled (legacy mode), uses context-specific tags:
+ * - <task> for initial task
+ * - <feedback> for user feedback
+ * - <answer> for follow-up question responses
+ */
+
+export type UserContentContext = "task" | "feedback" | "answer" | "resume"
+
+/**
+ * Get the opening tag for user content based on context and experiment setting
+ */
+export function getUserContentOpenTag(context: UserContentContext, useUnifiedTag: boolean): string {
+	if (useUnifiedTag) {
+		return "<user_message>"
+	}
+
+	switch (context) {
+		case "task":
+			return "<task>"
+		case "feedback":
+			return "<feedback>"
+		case "answer":
+			return "<answer>"
+		case "resume":
+			return "<user_message>"
+		default:
+			return "<user_message>"
+	}
+}
+
+/**
+ * Get the closing tag for user content based on context and experiment setting
+ */
+export function getUserContentCloseTag(context: UserContentContext, useUnifiedTag: boolean): string {
+	if (useUnifiedTag) {
+		return "</user_message>"
+	}
+
+	switch (context) {
+		case "task":
+			return "</task>"
+		case "feedback":
+			return "</feedback>"
+		case "answer":
+			return "</answer>"
+		case "resume":
+			return "</user_message>"
+		default:
+			return "</user_message>"
+	}
+}
+
+/**
+ * Wrap user content with appropriate tags
+ */
+export function wrapUserContent(content: string, context: UserContentContext, useUnifiedTag: boolean): string {
+	const openTag = getUserContentOpenTag(context, useUnifiedTag)
+	const closeTag = getUserContentCloseTag(context, useUnifiedTag)
+	return `${openTag}\n${content}\n${closeTag}`
+}
+
+/**
+ * Check if text contains any user content tags (for mention processing)
+ */
+export function hasUserContentTags(text: string, useUnifiedTag: boolean): boolean {
+	if (useUnifiedTag) {
+		return text.includes("<user_message>")
+	}
+
+	return (
+		text.includes("<task>") ||
+		text.includes("<feedback>") ||
+		text.includes("<answer>") ||
+		text.includes("<user_message>")
+	)
+}