feat(chat): add Reasoning heading and persistent timer; persist timing in message.metadata; render timer in UI

src/core/webview/webviewMessageHandler.ts

@@ -2865,6 +2865,35 @@ export const webviewMessageHandler = async (
 			}
 			break
 		}
+		case "updateMessageReasoningMeta": {
+			// Persist reasoning timer metadata on a specific message (by ts)
+			try {
+				const currentCline = provider.getCurrentTask()
+				if (!currentCline || !message.messageTs) {
+					break
+				}
+				const { messageIndex } = findMessageIndices(message.messageTs, currentCline)
+				if (messageIndex === -1) {
+					break
+				}
+				const msg = currentCline.clineMessages[messageIndex] as any
+				const existingMeta = (msg.metadata as any) || {}
+				const existingReasoning = existingMeta.reasoning || {}
+				msg.metadata = {
+					...existingMeta,
+					reasoning: { ...existingReasoning, ...(message.reasoningMeta || {}) },
+				}
+
+				await saveTaskMessages({
+					messages: currentCline.clineMessages,
+					taskId: currentCline.taskId,
+					globalStoragePath: provider.contextProxy.globalStorageUri.fsPath,
+				})
+			} catch (error) {
+				console.error("[updateMessageReasoningMeta] Failed to persist reasoning metadata:", error)
+			}
+			break
+		}
 		case "showMdmAuthRequiredNotification": {
 			// Show notification that organization requires authentication
 			vscode.window.showWarningMessage(t("common:mdm.info.organization_requires_auth"))

src/shared/WebviewMessage.ts

@@ -221,6 +221,7 @@ export interface WebviewMessage {
 		| "queueMessage"
 		| "removeQueuedMessage"
 		| "editQueuedMessage"
+		| "updateMessageReasoningMeta"
 	text?: string
 	editedMessageContent?: string
 	tab?: "settings" | "history" | "mcp" | "modes" | "chat" | "marketplace" | "cloud"
@@ -256,6 +257,10 @@ export interface WebviewMessage {
 	terminalOperation?: "continue" | "abort"
 	messageTs?: number
 	restoreCheckpoint?: boolean
+	reasoningMeta?: {
+		startedAt?: number
+		elapsedMs?: number
+	}
 	historyPreviewCollapsed?: boolean
 	filters?: { type?: string; search?: string; tags?: string[] }
 	settings?: any

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

@@ -1083,7 +1083,15 @@ export const ChatRowContent = ({
 						</div>
 					)
 				case "reasoning":
-					return <ReasoningBlock content={message.text || ""} />
+					return (
+						<ReasoningBlock
+							content={message.text || ""}
+							ts={message.ts}
+							isStreaming={isStreaming}
+							isLast={isLast}
+							metadata={message.metadata as any}
+						/>
+					)
 				case "api_req_started":
 					return (
 						<>

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

@@ -1,16 +1,89 @@
+import React, { useEffect, useMemo, useRef, useState } from "react"
+import { useTranslation } from "react-i18next"
+
 import MarkdownBlock from "../common/MarkdownBlock"
+import { vscode } from "@src/utils/vscode"
 
 interface ReasoningBlockProps {
 	content: string
+	ts: number
+	isStreaming: boolean
+	isLast: boolean
+	metadata?: Record<string, any>
+}
+
+function formatDuration(ms: number): string {
+	const totalSeconds = Math.max(0, Math.floor(ms / 1000))
+	const minutes = Math.floor(totalSeconds / 60)
+	const seconds = totalSeconds % 60
+	return `${minutes}:${seconds.toString().padStart(2, "0")}`
 }
 
 /**
- * Render reasoning as simple italic text, matching how <thinking> content is shown.
- * No borders, boxes, headers, timers, or collapsible behavior.
+ * Render reasoning with a heading and a persistent timer.
+ * - Heading uses i18n key chat:reasoning.thinking
+ * - Timer persists via message.metadata.reasoning { startedAt, elapsedMs }
  */
-export const ReasoningBlock = ({ content }: ReasoningBlockProps) => {
+export const ReasoningBlock = ({ content, ts, isStreaming, isLast, metadata }: ReasoningBlockProps) => {
+	const { t } = useTranslation()
+
+	const persisted = (metadata?.reasoning as { startedAt?: number; elapsedMs?: number } | undefined) || {}
+	const startedAtRef = useRef<number>(persisted.startedAt ?? Date.now())
+	const [elapsed, setElapsed] = useState<number>(persisted.elapsedMs ?? 0)
+
+	// Initialize startedAt on first mount if missing (persist to task)
+	useEffect(() => {
+		if (!persisted.startedAt && isLast) {
+			vscode.postMessage({
+				type: "updateMessageReasoningMeta",
+				messageTs: ts,
+				reasoningMeta: { startedAt: startedAtRef.current },
+			} as any)
+		}
+		// eslint-disable-next-line react-hooks/exhaustive-deps
+	}, [ts])
+
+	// Tick while active (last row and streaming)
+	useEffect(() => {
+		const active = isLast && isStreaming
+		if (!active) return
+
+		const tick = () => setElapsed(Date.now() - startedAtRef.current)
+		tick()
+		const id = setInterval(tick, 1000)
+		return () => clearInterval(id)
+	}, [isLast, isStreaming])
+
+	// Persist final elapsed when streaming stops
+	const wasActiveRef = useRef<boolean>(false)
+	useEffect(() => {
+		const active = isLast && isStreaming
+		if (wasActiveRef.current && !active) {
+			const finalMs = Date.now() - startedAtRef.current
+			setElapsed(finalMs)
+			vscode.postMessage({
+				type: "updateMessageReasoningMeta",
+				messageTs: ts,
+				reasoningMeta: { startedAt: startedAtRef.current, elapsedMs: finalMs },
+			} as any)
+		}
+		wasActiveRef.current = active
+	}, [isLast, isStreaming, ts])
+
+	const displayMs = useMemo(() => {
+		if (isLast && isStreaming) return elapsed
+		return persisted.elapsedMs ?? elapsed
+	}, [elapsed, isLast, isStreaming, persisted.elapsedMs])
+
 	return (
 		<div className="px-3 py-1">
+			<div className="flex items-center justify-between mb-1">
+				<div className="flex items-center gap-2">
+					<span className="codicon codicon-light-bulb text-muted-foreground" />
+					<span className="font-medium text-vscode-foreground">{t("chat:reasoning.thinking")}</span>
+				</div>
+				<span className="text-xs text-muted-foreground tabular-nums">{formatDuration(displayMs)}</span>
+			</div>
 			<div className="italic text-muted-foreground">
 				<MarkdownBlock markdown={content} />
 			</div>