fix: customization provider API rendering bugs and sessions window isolation (#307745)

* fix: add sequence counter to loadItems to prevent race conditions

Multiple concurrent loadItems() calls can overlap when autoruns fire
simultaneously. Without serialization, a slow earlier call can resolve
after the correct one and overwrite allItems with stale/empty results.
The sequence counter ensures only the latest call's result is applied.

* fix: add missing onDidChangeInstructions subscription

The list widget subscribed to onDidChangeCustomAgents,
onDidChangeSlashCommands, and onDidChangeSkills but not
onDidChangeInstructions. This meant instruction file discovery
completing after the initial load never triggered a widget refresh.

* fix: re-establish provider onDidChange when harness registers

The autorun that subscribes to itemProvider.onDidChange only read
activeHarness. If the harness ID was persisted from a previous session,
activeHarness never changed when the CLI harness registered, so the
subscription was never set up. Now also reads availableHarnesses to
re-fire when harnesses are added/removed.

* fix: add instruction groups to filterItemsForProvider

filterItemsForProvider only had storage-based groups (local, user,
extension, builtin). Provider-supplied instruction items have semantic
groupKey values like 'context-instructions' and 'on-demand-instructions'
which didn't match any group, causing all instruction items to be
silently dropped (allItems: 0). Add instruction-semantic groups when
the current section is Instructions, matching filterItemsForCore.

* fix: ignore customization provider API in sessions window

The sessions window manages its own harnesses via
SessionsCustomizationHarnessService and the remoteAgentHost
contribution. Extension-contributed harnesses via the provider API
should not be registered in the sessions window.

Author: joshspicer

src/vs/workbench/api/browser/mainThreadChatAgents2.ts

@@ -50,6 +50,7 @@ import { ICustomizationHarnessService, IExternalCustomizationItem, IExternalCust
 import { AICustomizationManagementSection, BUILTIN_STORAGE } from '../../contrib/chat/common/aiCustomizationWorkspaceService.js';
 import { IConfigurationService } from '../../../platform/configuration/common/configuration.js';
 import { IAgentPluginService } from '../../contrib/chat/common/plugins/agentPluginService.js';
+import { IWorkbenchEnvironmentService } from '../../services/environment/common/environmentService.js';
 
 interface AgentData {
 	dispose: () => void;
@@ -136,6 +137,7 @@ export class MainThreadChatAgents2 extends Disposable implements MainThreadChatA
 		@IConfigurationService private readonly _configurationService: IConfigurationService,
 		@ITelemetryService private readonly _telemetryService: ITelemetryService,
 		@IAgentPluginService private readonly _agentPluginService: IAgentPluginService,
+		@IWorkbenchEnvironmentService private readonly _environmentService: IWorkbenchEnvironmentService,
 	) {
 		super();
 		this._proxy = extHostContext.getProxy(ExtHostContext.ExtHostChatAgents2);
@@ -655,6 +657,11 @@ export class MainThreadChatAgents2 extends Disposable implements MainThreadChatA
 	}
 
 	async $registerChatSessionCustomizationProvider(handle: number, chatSessionType: string, metadata: IChatSessionCustomizationProviderMetadataDto, extensionId: ExtensionIdentifier): Promise<void> {
+		if (this._environmentService.isSessionsWindow) {
+			this._logService.trace(`[MainThreadChatAgents2] Sessions window does not use the customization provider API, ignoring registration from ${extensionId.value}`);
+			return;
+		}
+
 		if (!this._configurationService.getValue<boolean>('chat.customizations.providerApi.enabled')) {
 			this._logService.trace(`[MainThreadChatAgents2] Customization provider API is disabled, ignoring registration from ${extensionId.value}`);
 			return;

src/vs/workbench/contrib/chat/browser/aiCustomization/aiCustomizationListWidget.ts

@@ -586,6 +586,7 @@ export class AICustomizationListWidget extends Disposable {
 	private searchQuery: string = '';
 	private readonly collapsedGroups = new Set<string>();
 	private readonly dropdownActionDisposables = this._register(new DisposableStore());
+	private _loadItemsSeq = 0;
 
 	private readonly delayedFilter = new Delayer<void>(200);
 
@@ -646,11 +647,16 @@ export class AICustomizationListWidget extends Disposable {
 			this.refresh();
 		}));
 
-		// Subscribe to the active provider's onDidChange event
+		// Subscribe to the active provider's onDidChange event.
+		// Read both activeHarness and availableHarnesses so that the
+		// subscription is re-established when a new provider harness
+		// registers (availableHarnesses changes) even if activeHarness
+		// was already set to the harness id from persisted state.
 		const providerChangeDisposable = this._register(new MutableDisposable());
 		const syncChangeDisposable = this._register(new MutableDisposable());
 		this._register(autorun(reader => {
 			this.harnessService.activeHarness.read(reader);
+			this.harnessService.availableHarnesses.read(reader);
 			const activeDescriptor = this.harnessService.getActiveDescriptor();
 			if (activeDescriptor.itemProvider) {
 				providerChangeDisposable.value = activeDescriptor.itemProvider.onDidChange(() => this.refresh());
@@ -778,6 +784,7 @@ export class AICustomizationListWidget extends Disposable {
 		this._register(this.promptsService.onDidChangeCustomAgents(() => this.refresh()));
 		this._register(this.promptsService.onDidChangeSlashCommands(() => this.refresh()));
 		this._register(this.promptsService.onDidChangeSkills(() => this.refresh()));
+		this._register(this.promptsService.onDidChangeInstructions(() => this.refresh()));
 
 		// Refresh on file deletions so the list updates after inline delete actions
 		this._register(this.fileService.onDidFilesChange(e => {
@@ -1159,9 +1166,12 @@ export class AICustomizationListWidget extends Disposable {
 
 	/**
 	 * Loads items for the current section.
+	 * Uses a sequence counter so that stale results from concurrent
+	 * calls (e.g. overlapping autorun refreshes) are discarded.
 	 */
 	private async loadItems(): Promise<void> {
 		const section = this.currentSection;
+		const seq = ++this._loadItemsSeq;
 		let items: IAICustomizationListItem[];
 		try {
 			items = await this.fetchItemsForSection(section);
@@ -1170,8 +1180,8 @@ export class AICustomizationListWidget extends Disposable {
 			items = [];
 		}
 
-		if (this.currentSection !== section) {
-			return; // section changed while loading
+		if (this.currentSection !== section || this._loadItemsSeq !== seq) {
+			return; // section changed or a newer load started while loading
 		}
 
 		this.allItems = items;
@@ -1936,13 +1946,26 @@ export class AICustomizationListWidget extends Disposable {
 
 			this.displayEntries = entries;
 		} else {
-			// Standard provider layout: group by inferred storage/groupKey
-			const groups: { groupKey: string; label: string; icon: ThemeIcon; description: string; items: IAICustomizationListItem[] }[] = [
-				{ groupKey: PromptsStorage.local, label: localize('workspaceGroup', "Workspace"), icon: workspaceIcon, description: localize('workspaceGroupDescription', "Customizations stored as files in your project folder and shared with your team via version control."), items: [] },
-				{ groupKey: PromptsStorage.user, label: localize('userGroup', "User"), icon: userIcon, description: localize('userGroupDescription', "Customizations stored locally on your machine in a central location. Private to you and available across all projects."), items: [] },
-				{ groupKey: PromptsStorage.extension, label: localize('extensionGroup', "Extensions"), icon: extensionIcon, description: localize('extensionGroupDescription', "Read-only customizations provided by installed extensions."), items: [] },
-				{ groupKey: BUILTIN_STORAGE, label: localize('builtinGroup', "Built-in"), icon: builtinIcon, description: localize('builtinGroupDescription', "Built-in customizations shipped with the application."), items: [] },
-			];
+			// Standard provider layout: group by inferred storage/groupKey.
+			// Instructions use semantic categories (matching core path) so
+			// that provider-supplied groupKeys like 'context-instructions'
+			// are routed to the correct collapsible header.
+			const groups: { groupKey: string; label: string; icon: ThemeIcon; description: string; items: IAICustomizationListItem[] }[] =
+				this.currentSection === AICustomizationManagementSection.Instructions
+					? [
+						{ groupKey: 'agent-instructions', label: localize('agentInstructionsGroup', "Agent Instructions"), icon: instructionsIcon, description: localize('agentInstructionsGroupDescription', "Instruction files automatically loaded for all agent interactions (e.g. AGENTS.md, CLAUDE.md, copilot-instructions.md)."), items: [] },
+						{ groupKey: 'context-instructions', label: localize('contextInstructionsGroup', "Included Based on Context"), icon: instructionsIcon, description: localize('contextInstructionsGroupDescription', "Instructions automatically loaded when matching files are part of the context."), items: [] },
+						{ groupKey: 'on-demand-instructions', label: localize('onDemandInstructionsGroup', "Loaded on Demand"), icon: instructionsIcon, description: localize('onDemandInstructionsGroupDescription', "Instructions loaded only when explicitly referenced."), items: [] },
+						{ groupKey: PromptsStorage.local, label: localize('workspaceGroup', "Workspace"), icon: workspaceIcon, description: localize('workspaceGroupDescription', "Customizations stored as files in your project folder and shared with your team via version control."), items: [] },
+						{ groupKey: PromptsStorage.user, label: localize('userGroup', "User"), icon: userIcon, description: localize('userGroupDescription', "Customizations stored locally on your machine in a central location. Private to you and available across all projects."), items: [] },
+						{ groupKey: BUILTIN_STORAGE, label: localize('builtinGroup', "Built-in"), icon: builtinIcon, description: localize('builtinGroupDescription', "Built-in customizations shipped with the application."), items: [] },
+					]
+					: [
+						{ groupKey: PromptsStorage.local, label: localize('workspaceGroup', "Workspace"), icon: workspaceIcon, description: localize('workspaceGroupDescription', "Customizations stored as files in your project folder and shared with your team via version control."), items: [] },
+						{ groupKey: PromptsStorage.user, label: localize('userGroup', "User"), icon: userIcon, description: localize('userGroupDescription', "Customizations stored locally on your machine in a central location. Private to you and available across all projects."), items: [] },
+						{ groupKey: PromptsStorage.extension, label: localize('extensionGroup', "Extensions"), icon: extensionIcon, description: localize('extensionGroupDescription', "Read-only customizations provided by installed extensions."), items: [] },
+						{ groupKey: BUILTIN_STORAGE, label: localize('builtinGroup', "Built-in"), icon: builtinIcon, description: localize('builtinGroupDescription', "Built-in customizations shipped with the application."), items: [] },
+					];
 
 			for (const item of matchedItems) {
 				const key = item.groupKey ?? item.storage ?? PromptsStorage.local;