cache llm generated thinking headers (#304619)

* cache llm generated titles as fallback for rerendering

* store llm generated headers so cli will not re-generate

* address some comments, scope to non-local sessions

src/vs/workbench/contrib/chat/browser/widget/chatContentParts/chatSubagentContentPart.ts

@@ -116,7 +116,7 @@ export class ChatSubagentContentPart extends ChatCollapsibleContentPart implemen
 	 * Extracts subagent info (description, agentName, prompt) from a tool invocation.
 	 */
 	private static extractSubagentInfo(toolInvocation: IChatToolInvocation | IChatToolInvocationSerialized): { description: string; agentName: string | undefined; prompt: string | undefined; modelName: string | undefined } {
-		const defaultDescription = localize('chat.subagent.defaultDescription', 'Running subagent...');
+		const defaultDescription = localize('chat.subagent.defaultDescription', 'Running subagent');
 
 		// Only parent subagent tools contain the full subagent info
 		if (!ChatSubagentContentPart.isParentSubagentTool(toolInvocation)) {

src/vs/workbench/contrib/chat/browser/widget/chatContentParts/chatThinkingContentPart.ts

@@ -34,9 +34,11 @@ import { IChatMarkdownAnchorService } from './chatMarkdownAnchorService.js';
 import { ChatMessageRole, ILanguageModelsService } from '../../../common/languageModels.js';
 import './media/chatThinkingContent.css';
 import { IHoverService } from '../../../../../../platform/hover/browser/hover.js';
+import { IStorageService, StorageScope, StorageTarget } from '../../../../../../platform/storage/common/storage.js';
 import { extractImagesFromToolInvocationOutputDetails } from '../../../common/chatImageExtraction.js';
 import { IChatCollapsibleIODataPart } from './chatToolInputOutputContentPart.js';
 import { ChatThinkingExternalResourceWidget } from './chatThinkingExternalResourcesWidget.js';
+import { LocalChatSessionUri, chatSessionResourceToId } from '../../../common/model/chatUri.js';
 import { IEditSessionDiffStats } from '../../../common/editing/chatEditingService.js';
 
 
@@ -140,6 +142,10 @@ interface ILazyThinkingItem {
 type ILazyItem = ILazyToolItem | ILazyThinkingItem;
 const THINKING_SCROLL_MAX_HEIGHT = 200;
 
+const TITLE_CACHE_STORAGE_KEY = 'chat.thinkingTitleCache';
+const TITLE_CACHE_TTL_MS = 7 * 24 * 60 * 60 * 1000; // 7 days
+const TITLE_CACHE_MAX_ENTRIES = 1000;
+
 const enum WorkingMessageCategory {
 	Thinking = 'thinking',
 	Terminal = 'terminal',
@@ -284,6 +290,7 @@ export class ChatThinkingContentPart extends ChatCollapsibleContentPart implemen
 		@IChatMarkdownAnchorService private readonly chatMarkdownAnchorService: IChatMarkdownAnchorService,
 		@ILanguageModelsService private readonly languageModelsService: ILanguageModelsService,
 		@IHoverService hoverService: IHoverService,
+		@IStorageService private readonly storageService: IStorageService,
 	) {
 		const initialText = extractTextFromPart(content);
 		const extractedTitle = extractTitleFromThinkingContent(initialText)
@@ -897,6 +904,7 @@ export class ChatThinkingContentPart extends ChatCollapsibleContentPart implemen
 			return;
 		}
 
+		// Reuse any existing generated title from tool invocations or thinking parts.
 		const existingTitle = this.toolInvocations.find(t => t.generatedTitle)?.generatedTitle
 			?? this.allThinkingParts.find(t => t.generatedTitle)?.generatedTitle;
 		if (existingTitle) {
@@ -907,6 +915,27 @@ export class ChatThinkingContentPart extends ChatCollapsibleContentPart implemen
 			return;
 		}
 
+		// Only check the persisted cache when re-rendering
+		// (all tool invocations are serialized), not during live streaming.
+		const allSerialized = this.toolInvocations.length > 0
+			&& this.toolInvocations.every(t => t.kind === 'toolInvocationSerialized');
+		if (allSerialized) {
+			// Fallback: check the persisted title cache using the last tool call (non-local sessions only)
+			if (!LocalChatSessionUri.isLocalSession(this.element.sessionResource)) {
+				const lastToolInvocation = this.toolInvocations[this.toolInvocations.length - 1];
+				if (lastToolInvocation) {
+					const cachedTitle = this.getCachedTitle(lastToolInvocation.toolCallId);
+					if (cachedTitle) {
+						this.currentTitle = cachedTitle;
+						this.content.generatedTitle = cachedTitle;
+						this.setGeneratedTitleOnAllParts(cachedTitle);
+						this.setFinalizedTitle(cachedTitle);
+						return;
+					}
+				}
+			}
+		}
+
 		// case where we only have one item (tool or edit) in the thinking container and no thinking parts, we want to move it back to its original position
 		if (this.toolInvocationCount === 1 && this.hookCount === 0 && this.currentThinkingValue.trim() === '') {
 			// If singleItemInfo wasn't set (item was lazy/deferred), materialize it now
@@ -966,6 +995,55 @@ export class ChatThinkingContentPart extends ChatCollapsibleContentPart implemen
 		}
 	}
 
+	private loadTitleCache(): Record<string, { title: string; storedAt: number }> {
+		return this.storageService.getObject<Record<string, { title: string; storedAt: number }>>(TITLE_CACHE_STORAGE_KEY, StorageScope.PROFILE) ?? {};
+	}
+
+	private saveTitleCache(cache: Record<string, { title: string; storedAt: number }>): void {
+		if (Object.keys(cache).length === 0) {
+			this.storageService.remove(TITLE_CACHE_STORAGE_KEY, StorageScope.PROFILE);
+		} else {
+			this.storageService.store(TITLE_CACHE_STORAGE_KEY, JSON.stringify(cache), StorageScope.PROFILE, StorageTarget.MACHINE);
+		}
+	}
+
+	private getTitleCacheKey(toolCallId: string): string {
+		return `${chatSessionResourceToId(this.element.sessionResource)}:${toolCallId}`;
+	}
+
+	private getCachedTitle(toolCallId: string): string | undefined {
+		const entry = this.loadTitleCache()[this.getTitleCacheKey(toolCallId)];
+		if (!entry || (Date.now() - entry.storedAt) > TITLE_CACHE_TTL_MS) {
+			return undefined;
+		}
+		return entry.title;
+	}
+
+	private setCachedTitle(toolCallId: string, title: string): void {
+		const cache = this.loadTitleCache();
+		const now = Date.now();
+
+		// Evict expired entries on write
+		for (const key of Object.keys(cache)) {
+			if ((now - cache[key].storedAt) > TITLE_CACHE_TTL_MS) {
+				delete cache[key];
+			}
+		}
+
+		cache[this.getTitleCacheKey(toolCallId)] = { title, storedAt: now };
+
+		// Cap size by dropping oldest entries
+		const keys = Object.keys(cache);
+		if (keys.length > TITLE_CACHE_MAX_ENTRIES) {
+			const sorted = keys.sort((a, b) => cache[a].storedAt - cache[b].storedAt);
+			for (let i = 0; i < sorted.length - TITLE_CACHE_MAX_ENTRIES; i++) {
+				delete cache[sorted[i]];
+			}
+		}
+
+		this.saveTitleCache(cache);
+	}
+
 	private async generateTitleViaLLM(): Promise<void> {
 		const cts = new CancellationTokenSource();
 		const timeout = setTimeout(() => cts.cancel(), 5000);
@@ -1123,6 +1201,15 @@ ${this.hookCount > 0 ? `EXAMPLES WITH BLOCKED CONTENT (from hooks):
 				this.setFinalizedTitle(generatedTitle);
 				this.content.generatedTitle = generatedTitle;
 				this.setGeneratedTitleOnAllParts(generatedTitle);
+
+				// Persist to storage for non-local sessions only
+				if (!LocalChatSessionUri.isLocalSession(this.element.sessionResource)) {
+					const lastTool = this.toolInvocations[this.toolInvocations.length - 1];
+					if (lastTool) {
+						this.setCachedTitle(lastTool.toolCallId, generatedTitle);
+					}
+				}
+
 				return;
 			}
 		} catch (error) {

src/vs/workbench/contrib/chat/test/browser/widget/chatContentParts/chatSubagentContentPart.test.ts

@@ -144,7 +144,7 @@ suite('ChatSubagentContentPart', () => {
 				prompt: 'Test prompt'
 			},
 			originMessage: undefined,
-			invocationMessage: options.invocationMessage ?? 'Running subagent...',
+			invocationMessage: options.invocationMessage ?? 'Running subagent',
 			pastTenseMessage: undefined,
 			source: ToolDataSource.Internal,
 			toolId: options.toolId ?? RunSubagentTool.Id,
@@ -180,7 +180,7 @@ suite('ChatSubagentContentPart', () => {
 				result: 'Test result text'
 			},
 			originMessage: undefined,
-			invocationMessage: 'Running subagent...',
+			invocationMessage: 'Running subagent',
 			pastTenseMessage: undefined,
 			resultDetails: undefined,
 			isConfirmed: { type: ToolConfirmKind.ConfirmationNotNeeded },