Display model name in subagent session

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

@@ -143,7 +143,7 @@ export abstract class ChatCollapsibleContentPart extends Disposable implements I
 
 	abstract hasSameContent(other: IChatRendererContent, followingContent: IChatRendererContent[], element: ChatTreeItem): boolean;
 
-	private updateAriaLabel(element: HTMLElement, label: string, expanded?: boolean): void {
+	protected updateAriaLabel(element: HTMLElement, label: string, expanded?: boolean): void {
 		element.ariaLabel = label;
 		element.ariaExpanded = String(expanded);
 	}

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

@@ -133,6 +133,8 @@ export class ChatSubagentContentPart extends ChatCollapsibleContentPart implemen
 	// Persistent title elements for shimmer
 	private titleShimmerSpan: HTMLElement | undefined;
 	private titleDetailContainer: HTMLElement | undefined;
+	// Inline model name label shown in the collapsed title (e.g. "GPT-4o")
+	private modelLabelSpan: HTMLElement | undefined;
 	private readonly _titleDetailRendered = this._register(new MutableDisposable<IRenderedMarkdown>());
 
 	/**
@@ -232,6 +234,8 @@ export class ChatSubagentContentPart extends ChatCollapsibleContentPart implemen
 			this.titleShimmerSpan = $('span.chat-thinking-title-shimmer');
 			this.titleShimmerSpan.textContent = initialTitle;
 			labelElement.appendChild(this.titleShimmerSpan);
+			this.updateModelLabel(labelElement);
+			this.updateAriaLabel(this._collapseButton.element, initialTitle, this.isExpanded());
 		}
 
 		// Note: wrapper is created lazily in initContent(), so we can't set its style here
@@ -508,8 +512,8 @@ export class ChatSubagentContentPart extends ChatCollapsibleContentPart implemen
 			descSpan.textContent = ` ${this.description}`;
 			labelElement.appendChild(descSpan);
 
-			this._collapseButton.element.ariaLabel = shimmerText;
-			this._collapseButton.element.ariaExpanded = String(this.isExpanded());
+			this.updateModelLabel(labelElement);
+			this.updateAriaLabel(this._collapseButton.element, shimmerText, this.isExpanded());
 			return;
 		}
 
@@ -545,8 +549,69 @@ export class ChatSubagentContentPart extends ChatCollapsibleContentPart implemen
 		}
 
 		const fullLabel = `${shimmerText}${toolCallText}`;
-		this._collapseButton.element.ariaLabel = fullLabel;
-		this._collapseButton.element.ariaExpanded = String(this.isExpanded());
+		this.updateModelLabel(labelElement);
+		this.updateAriaLabel(this._collapseButton.element, fullLabel, this.isExpanded());
+	}
+
+	/**
+	 * Creates, updates, or removes the inline model name label in the collapsed
+	 * title. The label is appended last so it appears after the description and
+	 * any tool-call detail. It is updated in place to avoid duplication when the
+	 * title is re-rendered, and removed when no model name is available.
+	 */
+	private updateModelLabel(labelElement: HTMLElement): void {
+		if (this.modelName) {
+			if (!this.modelLabelSpan || this.modelLabelSpan.parentElement !== labelElement) {
+				this.modelLabelSpan = $('span.chat-subagent-model-label');
+				labelElement.appendChild(this.modelLabelSpan);
+			} else if (labelElement.lastChild !== this.modelLabelSpan) {
+				// Ensure it stays the last child so it renders after the title detail.
+				labelElement.appendChild(this.modelLabelSpan);
+			}
+			this.modelLabelSpan.textContent = this.modelName;
+		} else if (this.modelLabelSpan) {
+			this.modelLabelSpan.remove();
+			this.modelLabelSpan = undefined;
+		}
+	}
+
+	/**
+	 * Centralizes aria-label generation for the collapse button so that the
+	 * model name is announced to screen readers alongside the visible title.
+	 *
+	 * The base label is derived from what is actually rendered in the title
+	 * (excluding the inline model label) rather than the caller-provided
+	 * `label`. This keeps the accessible name in sync with the visible title
+	 * even when the base class re-applies its captured initial title from the
+	 * expand/collapse autorun after `updateTitle()` has changed it.
+	 */
+	protected override updateAriaLabel(element: HTMLElement, label: string, expanded?: boolean): void {
+		const baseLabel = this.getRenderedTitleText() || label;
+		const ariaLabel = this.modelName
+			? localize('chat.subagent.ariaWithModel', '{0}, model {1}', baseLabel, this.modelName)
+			: baseLabel;
+		super.updateAriaLabel(element, ariaLabel, expanded);
+	}
+
+	/**
+	 * Returns the text currently rendered in the collapse button's title,
+	 * excluding the inline model label span (which is announced separately via
+	 * the aria-label). Returns an empty string when the title has not been
+	 * rendered yet.
+	 */
+	private getRenderedTitleText(): string {
+		const labelElement = this._collapseButton?.labelElement;
+		if (!labelElement) {
+			return '';
+		}
+		let text = '';
+		for (const child of labelElement.childNodes) {
+			if (child === this.modelLabelSpan) {
+				continue;
+			}
+			text += child.textContent ?? '';
+		}
+		return text.trim();
 	}
 
 	private updateHover(): void {
@@ -605,6 +670,7 @@ export class ChatSubagentContentPart extends ChatCollapsibleContentPart implemen
 		if (modelName && modelName !== this.modelName) {
 			this.modelName = modelName;
 			this.updateHover();
+			this.updateTitle();
 		}
 	}
 

src/vs/workbench/contrib/chat/browser/widget/chatContentParts/media/chatSubagentContent.css

@@ -19,6 +19,13 @@
 		overflow: visible;
 	}
 
+	/* Inline model name shown in the collapsed title (e.g. "GPT-4o") */
+	.chat-subagent-model-label {
+		margin-left: 6px;
+		color: var(--vscode-descriptionForeground);
+		font-size: var(--vscode-chat-font-size-body-s);
+	}
+
 	/* Prompt and result section styling */
 	.chat-subagent-section {
 		padding: 4px 12px 4px 18px;

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

@@ -1725,4 +1725,219 @@ suite('ChatSubagentContentPart', () => {
 			assert.ok(modelHover, 'Should set up hover with model name after it arrives');
 		});
 	});
+
+	suite('Model name in title', () => {
+		function getModelLabels(part: ChatSubagentContentPart): HTMLElement[] {
+			const button = getCollapseButton(part);
+			const label = button ? getCollapseButtonLabel(button) : undefined;
+			if (!label) {
+				return [];
+			}
+			return Array.from(label.querySelectorAll('.chat-subagent-model-label')).filter(isHTMLElement);
+		}
+
+		test('should display the model name inline in the title when completed', () => {
+			const serializedInvocation = createMockSerializedToolInvocation({
+				toolSpecificData: {
+					kind: 'subagent',
+					description: 'Completed task',
+					agentName: 'TestAgent',
+					prompt: 'Do the thing',
+					result: 'Done',
+					modelName: 'GPT-4o'
+				}
+			});
+			const context = createMockRenderContext(true);
+
+			const part = createPart(serializedInvocation, context);
+
+			const labels = getModelLabels(part);
+			assert.strictEqual(labels.length, 1, 'Should render exactly one model label');
+			assert.strictEqual(labels[0].textContent, 'GPT-4o', 'Model label should show the model name');
+		});
+
+		test('should display the model name inline in the title while active', () => {
+			const toolInvocation = createMockToolInvocation({
+				toolSpecificData: {
+					kind: 'subagent',
+					description: 'Working on task',
+					agentName: 'TestAgent',
+					prompt: 'Do stuff',
+					modelName: 'Claude Sonnet 4'
+				},
+				stateType: IChatToolInvocation.StateKind.Executing,
+			});
+			const context = createMockRenderContext(false);
+
+			const part = createPart(toolInvocation, context);
+
+			const labels = getModelLabels(part);
+			assert.strictEqual(labels.length, 1, 'Should render exactly one model label while active');
+			assert.strictEqual(labels[0].textContent, 'Claude Sonnet 4', 'Model label should show the model name');
+		});
+
+		test('should not display a model label when no model name is available', () => {
+			const serializedInvocation = createMockSerializedToolInvocation({
+				toolSpecificData: {
+					kind: 'subagent',
+					description: 'Completed task',
+					agentName: 'TestAgent',
+					prompt: 'Do the thing',
+					result: 'Done',
+					// no modelName
+				}
+			});
+			const context = createMockRenderContext(true);
+
+			const part = createPart(serializedInvocation, context);
+
+			assert.strictEqual(getModelLabels(part).length, 0, 'Should not render a model label without a model name');
+		});
+
+		test('should include the model name in the aria-label', () => {
+			const serializedInvocation = createMockSerializedToolInvocation({
+				toolSpecificData: {
+					kind: 'subagent',
+					description: 'Completed task',
+					agentName: 'TestAgent',
+					prompt: 'Do the thing',
+					result: 'Done',
+					modelName: 'GPT-4o'
+				}
+			});
+			const context = createMockRenderContext(true);
+
+			const part = createPart(serializedInvocation, context);
+
+			const button = getCollapseButton(part);
+			const ariaLabel = button?.getAttribute('aria-label') ?? '';
+			assert.ok(ariaLabel.includes('GPT-4o'), `aria-label should include the model name, got: "${ariaLabel}"`);
+		});
+
+		test('should not include a model name in the aria-label when none is available', () => {
+			const serializedInvocation = createMockSerializedToolInvocation({
+				toolSpecificData: {
+					kind: 'subagent',
+					description: 'Completed task',
+					agentName: 'TestAgent',
+					prompt: 'Do the thing',
+					result: 'Done',
+					// no modelName
+				}
+			});
+			const context = createMockRenderContext(true);
+
+			const part = createPart(serializedInvocation, context);
+
+			const button = getCollapseButton(part);
+			const label = button ? getCollapseButtonLabel(button) : undefined;
+			const ariaLabel = button?.getAttribute('aria-label') ?? '';
+			const renderedTitle = (label?.textContent ?? '').trim();
+			assert.strictEqual(ariaLabel, renderedTitle,
+				`aria-label should match the rendered title when no model is available, got: "${ariaLabel}" vs "${renderedTitle}"`);
+			assert.strictEqual(getModelLabels(part).length, 0, 'Should not render a model label without a model name');
+		});
+
+		test('should add the model name to title and aria-label when it arrives after render', () => {
+			// Agent host subagents start without a model name; it is reported
+			// later via the child turns' usage events.
+			const toolSpecificData: IChatSubagentToolInvocationData = {
+				kind: 'subagent',
+				description: 'Working on task',
+				agentName: 'TestAgent',
+			};
+
+			const toolInvocation = createMockToolInvocation({
+				toolSpecificData,
+				stateType: IChatToolInvocation.StateKind.Executing,
+			});
+			const context = createMockRenderContext(false);
+
+			const part = createPart(toolInvocation, context);
+
+			assert.strictEqual(getModelLabels(part).length, 0, 'Should not render a model label before one is reported');
+
+			// Model name arrives while the subagent is still running
+			toolSpecificData.modelName = 'Claude Sonnet 4';
+			const state = toolInvocation.state as ReturnType<typeof observableValue<IChatToolInvocation.State>>;
+			state.set(createState(IChatToolInvocation.StateKind.Executing), undefined);
+
+			const labels = getModelLabels(part);
+			assert.strictEqual(labels.length, 1, 'Should render exactly one model label after it arrives (no duplication)');
+			assert.strictEqual(labels[0].textContent, 'Claude Sonnet 4', 'Model label should show the new model name');
+
+			const button = getCollapseButton(part);
+			const ariaLabel = button?.getAttribute('aria-label') ?? '';
+			assert.ok(ariaLabel.includes('Claude Sonnet 4'), `aria-label should include the model name after it arrives, got: "${ariaLabel}"`);
+		});
+
+		test('should not duplicate the model label after expand and collapse', () => {
+			const serializedInvocation = createMockSerializedToolInvocation({
+				toolSpecificData: {
+					kind: 'subagent',
+					description: 'Completed task',
+					agentName: 'TestAgent',
+					prompt: 'Do the thing',
+					result: 'Done',
+					modelName: 'GPT-4o'
+				}
+			});
+			const context = createMockRenderContext(true);
+
+			const part = createPart(serializedInvocation, context);
+
+			const button = getCollapseButton(part);
+			assert.ok(button, 'Should have collapse button');
+			button.click(); // expand
+			button.click(); // collapse
+			part.finalizeTitle();
+
+			const labels = getModelLabels(part);
+			assert.strictEqual(labels.length, 1, 'Should still render exactly one model label after expand/collapse');
+			assert.strictEqual(labels[0].textContent, 'GPT-4o', 'Model label should still show the model name');
+		});
+
+		test('should keep the aria-label in sync with the updated title after expand/collapse', () => {
+			const toolSpecificData: IChatSubagentToolInvocationData = {
+				kind: 'subagent',
+				description: 'Initial description',
+				agentName: 'TestAgent',
+				prompt: 'Do stuff',
+				modelName: 'GPT-4o',
+			};
+
+			const toolInvocation = createMockToolInvocation({
+				toolSpecificData,
+				stateType: IChatToolInvocation.StateKind.Executing,
+			});
+			const context = createMockRenderContext(false);
+
+			const part = createPart(toolInvocation, context);
+
+			// Update the title with a running tool message (this is the more
+			// accurate, current label).
+			part.trackToolState(createMockToolInvocation({
+				toolSpecificData,
+				stateType: IChatToolInvocation.StateKind.Executing,
+				invocationMessage: 'Reading config.ts',
+			}));
+
+			const button = getCollapseButton(part);
+			assert.ok(button, 'Should have collapse button');
+
+			// Toggling expansion triggers the base class autorun, which previously
+			// re-applied the stale initial title to the aria-label.
+			button.click(); // expand
+			button.click(); // collapse
+
+			const ariaLabel = button.getAttribute('aria-label') ?? '';
+			assert.ok(ariaLabel.includes('Reading config.ts'),
+				`aria-label should reflect the updated title after expand/collapse, got: "${ariaLabel}"`);
+			assert.ok(ariaLabel.includes('GPT-4o'),
+				`aria-label should still include the model name after expand/collapse, got: "${ariaLabel}"`);
+			// The model name must not be duplicated in the aria-label.
+			assert.strictEqual(ariaLabel.indexOf('GPT-4o'), ariaLabel.lastIndexOf('GPT-4o'),
+				`aria-label should not duplicate the model name, got: "${ariaLabel}"`);
+		});
+	});
 });