feat: add collapsible reasoning blocks with auto-expand setting

- Added autoExpandReasoningBlocks configuration setting to control default expansion state
- Created CollapsibleReasoningBlock component that wraps ReasoningBlock with collapsible UI
- Updated ChatRow to use CollapsibleReasoningBlock instead of ReasoningBlock
- Added preview text display when reasoning block is collapsed
- Integrated with ExtensionStateContext for settings management

Fixes #7873

packages/types/src/global-settings.ts

@@ -67,6 +67,7 @@ export const globalSettingsSchema = z.object({
 	alwaysAllowFollowupQuestions: z.boolean().optional(),
 	followupAutoApproveTimeoutMs: z.number().optional(),
 	alwaysAllowUpdateTodoList: z.boolean().optional(),
+	autoExpandReasoningBlocks: z.boolean().optional(),
 	allowedCommands: z.array(z.string()).optional(),
 	deniedCommands: z.array(z.string()).optional(),
 	commandExecutionTimeout: z.number().optional(),

src/core/webview/webviewMessageHandler.ts

@@ -1553,6 +1553,10 @@ export const webviewMessageHandler = async (
 			await updateGlobalState("alwaysAllowFollowupQuestions", message.bool ?? false)
 			await provider.postStateToWebview()
 			break
+		case "autoExpandReasoningBlocks":
+			await updateGlobalState("autoExpandReasoningBlocks", message.bool ?? false)
+			await provider.postStateToWebview()
+			break
 		case "followupAutoApproveTimeoutMs":
 			await updateGlobalState("followupAutoApproveTimeoutMs", message.value)
 			await provider.postStateToWebview()

src/shared/ExtensionMessage.ts

@@ -229,6 +229,7 @@ export type ExtensionState = Pick<
 	| "alwaysAllowExecute"
 	| "alwaysAllowUpdateTodoList"
 	| "followupAutoApproveTimeoutMs"
+	| "autoExpandReasoningBlocks"
 	| "allowedCommands"
 	| "deniedCommands"
 	| "allowedMaxRequests"

src/shared/WebviewMessage.ts

@@ -49,6 +49,7 @@ export interface WebviewMessage {
 		| "alwaysAllowFollowupQuestions"
 		| "alwaysAllowUpdateTodoList"
 		| "followupAutoApproveTimeoutMs"
+		| "autoExpandReasoningBlocks"
 		| "webviewDidLaunch"
 		| "newTask"
 		| "askResponse"

webview-ui/src/components/chat/ChatRow.tsx

@@ -24,7 +24,7 @@ import UpdateTodoListToolBlock from "./UpdateTodoListToolBlock"
 import CodeAccordian from "../common/CodeAccordian"
 import CodeBlock from "../common/CodeBlock"
 import MarkdownBlock from "../common/MarkdownBlock"
-import { ReasoningBlock } from "./ReasoningBlock"
+import { CollapsibleReasoningBlock } from "./CollapsibleReasoningBlock"
 import Thumbnails from "../common/Thumbnails"
 import ImageBlock from "../common/ImageBlock"
 
@@ -1084,7 +1084,7 @@ export const ChatRowContent = ({
 					)
 				case "reasoning":
 					return (
-						<ReasoningBlock
+						<CollapsibleReasoningBlock
 							content={message.text || ""}
 							ts={message.ts}
 							isStreaming={isStreaming}

webview-ui/src/components/chat/CollapsibleReasoningBlock.tsx

@@ -0,0 +1,82 @@
+import React, { useState, useEffect, useContext } from "react"
+import { ChevronDown, ChevronRight } from "lucide-react"
+import { Collapsible, CollapsibleContent, CollapsibleTrigger } from "../ui/collapsible"
+import { ExtensionStateContext } from "../../context/ExtensionStateContext"
+import { ReasoningBlock } from "./ReasoningBlock"
+
+interface CollapsibleReasoningBlockProps {
+	content: string
+	ts: number
+	isStreaming: boolean
+	isLast: boolean
+	metadata?: any
+}
+
+export const CollapsibleReasoningBlock: React.FC<CollapsibleReasoningBlockProps> = ({
+	content,
+	ts,
+	isStreaming,
+	isLast,
+	metadata,
+}) => {
+	const extensionState = useContext(ExtensionStateContext)
+	const autoExpand = extensionState?.autoExpandReasoningBlocks ?? false
+
+	// Start with the configured default state
+	const [isOpen, setIsOpen] = useState(autoExpand)
+
+	// Update when the setting changes
+	useEffect(() => {
+		setIsOpen(autoExpand)
+	}, [autoExpand])
+
+	// Extract first line or preview of the reasoning content
+	const getPreviewText = () => {
+		if (!content) return "Thinking..."
+		const lines = content.split("\n").filter((line) => line.trim())
+		if (lines.length === 0) return "Thinking..."
+
+		// Get first meaningful line (skip empty lines)
+		const firstLine = lines[0]
+		const maxLength = 100
+
+		if (firstLine.length > maxLength) {
+			return firstLine.substring(0, maxLength) + "..."
+		}
+		return firstLine + (lines.length > 1 ? "..." : "")
+	}
+
+	return (
+		<Collapsible open={isOpen} onOpenChange={setIsOpen}>
+			<div className="bg-vscode-editorWidget-background border border-vscode-editorWidget-border rounded-md overflow-hidden">
+				<CollapsibleTrigger className="flex items-center justify-between w-full p-3 hover:bg-vscode-list-hoverBackground transition-colors">
+					<div className="flex items-center gap-2">
+						{isOpen ? (
+							<ChevronDown className="h-4 w-4 text-vscode-descriptionForeground" />
+						) : (
+							<ChevronRight className="h-4 w-4 text-vscode-descriptionForeground" />
+						)}
+						<span className="text-sm font-medium text-vscode-descriptionForeground">Reasoning</span>
+						{!isOpen && (
+							<span className="text-sm text-vscode-descriptionForeground ml-2 truncate max-w-[500px]">
+								{getPreviewText()}
+							</span>
+						)}
+					</div>
+				</CollapsibleTrigger>
+
+				<CollapsibleContent>
+					<div className="border-t border-vscode-editorWidget-border">
+						<ReasoningBlock
+							content={content}
+							ts={ts}
+							isStreaming={isStreaming}
+							isLast={isLast}
+							metadata={metadata}
+						/>
+					</div>
+				</CollapsibleContent>
+			</div>
+		</Collapsible>
+	)
+}