Skip extension host restart when adding the first folder to an empty window - #334812

Fixes #319944

Problem

When a window has no folder open and you Add Folder to Workspace, VS Code restarts the extension host. If Copilot Chat (or another session) is in progress, you get Please confirm restart of extensions — A session is in progress. Confirming kills the chat.

N→N+1 folders in an existing multi-root workspace does not restart the host. 0→1 should behave the same.

Two restarts fire on that transition:

1. NativeWorkspaceEditingService.enterWorkspace — reason Opening a multi-root workspace (empty window always creates an untitled workspace and enters it).
2. WorkspaceChangeExtHostRelauncher — reason Changing workspace folders (first folder goes from none → one, for the deprecated workspace.rootPath API).

Skipping only (1) is not enough. Local logs still showed the veto from (2):

Extension host was not stopped because of veto (stop reason: Changing workspace folders, veto reason: A session is in progress.)

Fix

Skip the extension host restart on the 0→1 path only. Storage switch, backup reinit, and onDidEnterWorkspace still run. Changing the first folder later (A → B) still restarts the host. Folder → multi-root and remote windows are unchanged.

workspaceEditingService.ts — do not stop/start the EH when coming from WorkbenchState.EMPTY:

const fromEmptyWorkspace = this.contextService.getWorkbenchState() === WorkbenchState.EMPTY;

if (!fromEmptyWorkspace) {
	const stopped = await this.extensionService.stopExtensionHosts(/* ... */);
	if (!stopped) {
		return;
	}
}

relauncher.contribution.ts — do not schedule a restart when there was no previous first folder:

const hadFirstFolder = !!this.firstFolderResource;
this.firstFolderResource = newFirstFolderResource;

// Skip 0→1 folders (#319944): same as adding a folder in an existing workspace
if (hadFirstFolder) {
	this.extensionHostRestarter.schedule();
}

Notes:

• Workspace folders still update live via $acceptWorkspaceData (MainThreadWorkspace), same as N→N+1.
• Chat session files still migrate through ChatSessionStore joining onDidEnterWorkspace.
• Caveat: extension-host workspace-scoped storage (ExtensionStoragePaths) stays bound to the empty-window workspace id until the next real EH restart. Workbench storage is switched with preserveData. Extensions that only read rootPath in activate() can stay stale until then (same class of issue as in-place folder add).

Tests

• nativeWorkspaceEditingService.test.ts
  • empty window → enterWorkspace does not call stopExtensionHosts / startExtensionHosts
  • folder window → enterWorkspace still restarts the host

How to test

1. ./scripts/code.sh with no folder (empty window).
2. Start Copilot Chat and send a message.
3. Command Palette → Add Folder to Workspace... → pick a folder.
4. No restart confirmation dialog; chat stays.

Regression: open a single folder, add a second folder via Add Folder to Workspace — EH restart for enterWorkspace still applies. In an existing multi-root workspace, adding another folder (not replacing the first) still does not restart.