Very rough proof-of-concept of subtask communication

src/core/Cline.ts

@@ -75,6 +75,7 @@ type UserContent = Array<
 
 export class Cline {
 	readonly taskId: string
+	readonly parentTaskId?: string
 	api: ApiHandler
 	private terminalManager: TerminalManager
 	private urlContentFetcher: UrlContentFetcher
@@ -129,12 +130,14 @@ export class Cline {
 		images?: string[] | undefined,
 		historyItem?: HistoryItem | undefined,
 		experiments?: Record<string, boolean>,
+		parentTaskId?: string,
 	) {
 		if (!task && !images && !historyItem) {
 			throw new Error("Either historyItem or task/images must be provided")
 		}
 
 		this.taskId = crypto.randomUUID()
+		this.parentTaskId = parentTaskId
 		this.api = buildApiHandler(apiConfiguration)
 		this.terminalManager = new TerminalManager()
 		this.urlContentFetcher = new UrlContentFetcher(provider.context)
@@ -2553,7 +2556,7 @@ export class Cline {
 								const provider = this.providerRef.deref()
 								if (provider) {
 									await provider.handleModeSwitch(mode)
-									await provider.initClineWithTask(message)
+									await provider.initClineWithTask(message, undefined, this.taskId)
 									pushToolResult(
 										`Successfully created new task in ${targetMode.name} mode with message: ${message}`,
 									)
@@ -2667,10 +2670,22 @@ export class Cline {
 									await this.say("completion_result", result, undefined, false)
 								}
 
+								// If this is a child task, return result to parent
+								if (this.parentTaskId) {
+									const provider = this.providerRef.deref()
+									if (provider) {
+										try {
+											await provider.handleTaskResult(this.parentTaskId, result)
+										} catch (error) {
+											console.error("Failed to return result to parent task:", error)
+										}
+									}
+								}
+
 								// we already sent completion_result says, an empty string asks relinquishes control over button and field
 								const { response, text, images } = await this.ask("completion_result", "", false)
 								if (response === "yesButtonClicked") {
-									pushToolResult("") // signals to recursive loop to stop (for now this never happens since yesButtonClicked will trigger a new task)
+									pushToolResult("") // signals to recursive loop to stop
 									break
 								}
 								await this.say("user_feedback", text ?? "", images)

src/core/webview/ClineProvider.ts

@@ -18,7 +18,7 @@ import WorkspaceTracker from "../../integrations/workspace/WorkspaceTracker"
 import { McpHub } from "../../services/mcp/McpHub"
 import { ApiConfiguration, ApiProvider, ModelInfo } from "../../shared/api"
 import { findLast } from "../../shared/array"
-import { ApiConfigMeta, ExtensionMessage } from "../../shared/ExtensionMessage"
+import { ApiConfigMeta, ExtensionMessage, ClineMessage } from "../../shared/ExtensionMessage"
 import { HistoryItem } from "../../shared/HistoryItem"
 import { checkoutDiffPayloadSchema, checkoutRestorePayloadSchema, WebviewMessage } from "../../shared/WebviewMessage"
 import { Mode, CustomModePrompts, PromptComponent, defaultModeSlug } from "../../shared/modes"
@@ -277,7 +277,7 @@ export class ClineProvider implements vscode.WebviewViewProvider {
 			return
 		}
 
-		await visibleProvider.initClineWithTask(prompt)
+		await visibleProvider.initClineWithTask(prompt, undefined, undefined)
 	}
 
 	public static async handleTerminalAction(
@@ -397,7 +397,80 @@ export class ClineProvider implements vscode.WebviewViewProvider {
 		this.outputChannel.appendLine("Webview view resolved")
 	}
 
-	public async initClineWithTask(task?: string, images?: string[]) {
+	/**
+	 * Adds a child task's result as a text message to a parent task's messages and saves it
+	 */
+	private async addChildTaskResultToParent(taskId: string, result: string): Promise<void> {
+		const taskDir = path.join(this.context.globalStorageUri.fsPath, "tasks", taskId)
+		const messagesPath = path.join(taskDir, GlobalFileNames.uiMessages)
+
+		// Read existing messages
+		let messages: ClineMessage[] = []
+		if (await fileExistsAtPath(messagesPath)) {
+			messages = JSON.parse(await fs.readFile(messagesPath, "utf8"))
+		}
+
+		// Add result as text message from child task
+		messages.push({
+			ts: Date.now(),
+			type: "say",
+			say: "text",
+			text: result,
+		})
+
+		// Save updated messages
+		await fs.writeFile(messagesPath, JSON.stringify(messages))
+	}
+
+	/**
+	 * Handles returning a result to a parent task
+	 */
+	public async handleTaskResult(parentTaskId: string, result: string): Promise<void> {
+		try {
+			// Get parent task data
+			const { historyItem, apiConversationHistory } = await this.getTaskWithId(parentTaskId)
+
+			// Add text message to parent task's UI messages
+			await this.addChildTaskResultToParent(parentTaskId, result)
+
+			// Add message to parent task's API conversation history
+			const message: Anthropic.MessageParam & { ts?: number } = {
+				role: "assistant",
+				content: [
+					{
+						type: "text",
+						text: result,
+					},
+				],
+				ts: Date.now(),
+			}
+			apiConversationHistory.push(message)
+
+			// Save updated API conversation history
+			const taskDir = path.join(this.context.globalStorageUri.fsPath, "tasks", parentTaskId)
+			const apiHistoryPath = path.join(taskDir, GlobalFileNames.apiConversationHistory)
+			await fs.writeFile(apiHistoryPath, JSON.stringify(apiConversationHistory))
+
+			// Switch back to parent task
+			await this.initClineWithHistoryItem(historyItem)
+			await this.postMessageToWebview({
+				type: "action",
+				action: "chatButtonClicked",
+			})
+			// Wait for chat view to load before clicking the button
+			await delay(300)
+			// Hit the primary button to continue the parent task
+			await this.postMessageToWebview({
+				type: "invoke",
+				invoke: "primaryButtonClick",
+			})
+		} catch (error) {
+			this.outputChannel.appendLine(`Failed to handle task result: ${error}`)
+			throw error
+		}
+	}
+
+	public async initClineWithTask(task?: string, images?: string[], parentTaskId?: string) {
 		await this.clearTask()
 		const {
 			apiConfiguration,
@@ -424,6 +497,7 @@ export class ClineProvider implements vscode.WebviewViewProvider {
 			images,
 			undefined,
 			experiments,
+			parentTaskId,
 		)
 	}
 
@@ -774,7 +848,9 @@ export class ClineProvider implements vscode.WebviewViewProvider {
 						// Could also do this in extension .ts
 						//this.postMessageToWebview({ type: "text", text: `Extension: ${Date.now()}` })
 						// initializing new instance of Cline will make sure that any agentically running promises in old instance don't affect our new task. this essentially creates a fresh slate for the new task
-						await this.initClineWithTask(message.text, message.images)
+						// Pass the current task's ID as the parent ID if it exists
+						const parentTaskId = this.cline?.taskId
+						await this.initClineWithTask(message.text, message.images, parentTaskId)
 						break
 					case "apiConfiguration":
 						if (message.apiConfiguration) {

src/shared/HistoryItem.ts

@@ -8,4 +8,5 @@ export type HistoryItem = {
 	cacheReads?: number
 	totalCost: number
 	size?: number
+	parentTaskId?: string // ID of the parent task if this was created via new_task
 }