fix: show Preview as icon in turn changes summary

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

@@ -414,7 +414,7 @@ class CollapsibleChangesSummaryListRenderer implements IListRenderer<IEditSessio
 
 		if (templateData.actionBar && this.options?.getRowActions) {
 			templateData.actionBar.clear();
-			templateData.actionBar.push(this.options.getRowActions(data), { icon: false, label: true });
+			templateData.actionBar.push(this.options.getRowActions(data), { icon: true, label: false });
 		}
 	}
 

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

@@ -5,7 +5,7 @@
 
 import * as dom from '../../../../../../base/browser/dom.js';
 import { $ } from '../../../../../../base/browser/dom.js';
-import { IAction, toAction } from '../../../../../../base/common/actions.js';
+import { IAction } from '../../../../../../base/common/actions.js';
 import { Codicon } from '../../../../../../base/common/codicons.js';
 import { combinedDisposable, Disposable, IDisposable } from '../../../../../../base/common/lifecycle.js';
 import { autorun, constObservable, derived, derivedOpts, IObservable } from '../../../../../../base/common/observable.js';
@@ -26,7 +26,7 @@ import { IEditSessionEntryDiff } from '../../../common/editing/chatEditingServic
 import { IChatRendererContent, IChatTurnPillsPart } from '../../../common/model/chatViewModel.js';
 import { ChatTreeItem } from '../../chat.js';
 import { IChatResponseFileChangesService, IChatResponseFileEdit } from '../../chatResponseFileChangesService.js';
-import { diffStatsEqual, EMPTY_DIFF_STATS, IDiffStats, IPreviewFile, observeTurnStatusPillsEnabled, openChatTurnFile, previewFilesEqual, previewKind } from '../chatTurnPills.js';
+import { diffStatsEqual, EMPTY_DIFF_STATS, IDiffStats, IPreviewFile, createTurnChangesPreviewActions, observeTurnStatusPillsEnabled, openChatTurnFile, previewFilesEqual, previewKind } from '../chatTurnPills.js';
 import { renderChangesSummaryFileList } from './chatChangesSummaryPart.js';
 import { ChatCollapsibleContentPart } from './chatCollapsibleContentPart.js';
 import { IChatContentPart, IChatContentPartRenderContext } from './chatContentParts.js';
@@ -254,20 +254,11 @@ export class ChatTurnPillsContentPart extends Disposable implements IChatContent
 	}
 
 	/**
-	 * Row actions for the changed-files list: previewable files get a labelless,
-	 * icon-free action that opens the file.
+	 * Row actions for the changed-files list: previewable files get an icon-only
+	 * Preview action that opens the file.
 	 */
 	private _getRowActions(diff: IEditSessionEntryDiff): IAction[] {
-		const kind = previewKind(diff.modifiedURI);
-		if (!kind) {
-			return [];
-		}
-		const file: IPreviewFile = { uri: diff.modifiedURI, kind, created: isEqual(diff.originalURI, diff.modifiedURI) };
-		return [toAction({
-			id: 'chat.turnChanges.previewFile',
-			label: localize('chat.turnChanges.preview', "Preview"),
-			run: () => openChatTurnFile(file, this._openerService, this._configurationService),
-		})];
+		return createTurnChangesPreviewActions(diff.modifiedURI, diff.originalURI, this._openerService, this._configurationService);
 	}
 
 	hasSameContent(other: IChatRendererContent, _followingContent: IChatRendererContent[], _element: ChatTreeItem): boolean {

src/vs/workbench/contrib/chat/browser/widget/chatTurnPills.ts

@@ -107,6 +107,29 @@ export async function openChatTurnFile(file: IPreviewFile, openerService: IOpene
 	});
 }
 
+/**
+ * Row actions for the expanded turn-changes file list.
+ * Previewable files get an icon-only Preview action (`Codicon.openPreview`).
+ */
+export function createTurnChangesPreviewActions(
+	modifiedURI: URI,
+	originalURI: URI,
+	openerService: IOpenerService,
+	configurationService: IConfigurationService,
+): IAction[] {
+	const kind = previewKind(modifiedURI);
+	if (!kind) {
+		return [];
+	}
+	const file: IPreviewFile = { uri: modifiedURI, kind, created: isEqual(originalURI, modifiedURI) };
+	return [toAction({
+		id: 'chat.turnChanges.previewFile',
+		label: localize('chat.turnChanges.preview', "Preview"),
+		class: ThemeIcon.asClassName(Codicon.openPreview),
+		run: () => openChatTurnFile(file, openerService, configurationService),
+	})];
+}
+
 /** The data and interactions a {@link ChatTurnPillsWidget} reflects. */
 export interface IChatTurnPillsModel {
 	readonly stats: IObservable<IDiffStats>;

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

@@ -3217,7 +3217,7 @@ have to be updated for changes to the rules above, or to support more deeply nes
 	width: 16px;
 }
 
-/* Per-row action bar in the changed-files list (e.g. the "Preview" action). The
+/* Per-row action bar in the changed-files list (e.g. the Preview icon). The
 	row becomes a flex row so the file label fills the remaining width, followed
 	by the actions and the right-aligned change counts. Scoped via the class the
 	renderer adds only when a row-action provider is supplied. */
@@ -3242,12 +3242,15 @@ have to be updated for changes to the rules above, or to support more deeply nes
 }
 
 .interactive-session .chat-summary-list-actions .action-label {
-	color: var(--vscode-textLink-foreground);
+	color: var(--vscode-icon-foreground);
 	cursor: pointer;
+	border-radius: 4px;
+	padding: 2px;
 }
 
 .interactive-session .chat-summary-list-actions .action-label:hover {
-	color: var(--vscode-textLink-activeForeground);
+	background-color: var(--vscode-toolbar-hoverBackground);
+	color: var(--vscode-icon-foreground);
 }
 
 .interactive-session .chat-used-context {

src/vs/workbench/contrib/chat/test/browser/widget/chatTurnPills.test.ts

@@ -10,7 +10,7 @@ import { ensureNoDisposablesAreLeakedInTestSuite } from '../../../../../../base/
 import { TestConfigurationService } from '../../../../../../platform/configuration/test/common/testConfigurationService.js';
 import { IOpenerService, OpenExternalOptions, OpenInternalOptions } from '../../../../../../platform/opener/common/opener.js';
 import { BrowserViewEditorId } from '../../../../browserView/common/browserView.js';
-import { openChatTurnFile, previewKind } from '../../../browser/widget/chatTurnPills.js';
+import { createTurnChangesPreviewActions, openChatTurnFile, previewKind } from '../../../browser/widget/chatTurnPills.js';
 import { ChatConfiguration } from '../../../common/constants.js';
 
 suite('ChatTurnPills', () => {
@@ -44,6 +44,60 @@ suite('ChatTurnPills', () => {
 		});
 	});
 
+	suite('createTurnChangesPreviewActions (#328520)', () => {
+		const openerService = new class extends mock<IOpenerService>() {
+			override async open(): Promise<boolean> {
+				return true;
+			}
+		};
+		const configurationService = new TestConfigurationService();
+
+		test('returns an icon-only Preview action for markdown files', () => {
+			const modified = URI.file('/workspace/docs/AI_CUSTOMIZATIONS.md');
+			const actions = createTurnChangesPreviewActions(modified, URI.file('/workspace/other.md'), openerService, configurationService);
+
+			assert.strictEqual(actions.length, 1);
+			assert.strictEqual(actions[0].id, 'chat.turnChanges.previewFile');
+			assert.strictEqual(actions[0].label, 'Preview');
+			assert.ok(actions[0].class?.includes('codicon-open-preview'), `expected open-preview icon class, got: ${actions[0].class}`);
+		});
+
+		test('returns no actions for non-previewable files', () => {
+			const modified = URI.file('/workspace/src/service.ts');
+			const actions = createTurnChangesPreviewActions(modified, modified, openerService, configurationService);
+			assert.deepStrictEqual(actions, []);
+		});
+
+		test('run opens the markdown file via chat editor associations', async () => {
+			const resource = URI.file('/workspace/README.md');
+			let opened: { resource: string; options: OpenInternalOptions | OpenExternalOptions | undefined } | undefined;
+			const trackingOpener = new class extends mock<IOpenerService>() {
+				override async open(resource: string | URI, options?: OpenInternalOptions | OpenExternalOptions): Promise<boolean> {
+					opened = { resource: resource.toString(), options };
+					return true;
+				}
+			};
+			const config = new TestConfigurationService({
+				[ChatConfiguration.EditorAssociations]: {
+					'*.md': 'vscode.markdown.editor',
+				},
+			});
+
+			const actions = createTurnChangesPreviewActions(resource, resource, trackingOpener, config);
+			await actions[0].run();
+
+			assert.deepStrictEqual(opened, {
+				resource: resource.toString(),
+				options: {
+					fromUserGesture: true,
+					editorOptions: {
+						override: 'vscode.markdown.editor',
+					},
+				},
+			});
+		});
+	});
+
 	test('classifies supported preview resources', () => {
 		assert.deepStrictEqual([
 			previewKind(URI.file('/workspace/README.md'), true),

src/vs/workbench/test/browser/componentFixtures/chat/chatTurnPills.fixture.ts

@@ -155,12 +155,14 @@ export default defineThemedFixtureGroup({ path: 'chat/' }, {
 			}),
 		}),
 
-		// The external README remains in the preview pill and out of the expanded
-		// workspace changes list.
+		// Expanded workspace changes list. External README stays in the preview
+		// pill (not this list). Workspace markdown rows get the per-row Preview
+		// icon; non-md rows have no row action.
 		ChangesAndExternalPreview_Expanded: defineComponentFixture({
 			render: (ctx) => renderTurnPills(ctx, {
 				expanded: true,
 				diffs: [
+					fileDiff('docs.md', 12, 2, true),
 					fileDiff('index.html', 30, 4, true),
 					fileDiff('app.ts', 8, 3, false),
 					fileDiff('styles.css', 4, 1, false),