src/vs/workbench/api/browser/mainThreadEditorTabs.ts/MainThreadEditorTabs/_onDidTabOpen
class MainThreadEditorTabs:	private _onDidTabOpen(groupId: number, editorInput: EditorInput, editorIndex: number) {
		const group = this._editorGroupsService.getGroup(groupId);
		// Even if the editor service knows about the group the group might not exist yet in our model
		const groupInModel = this._groupLookup.get(groupId) !== undefined;
		// Means a new group was likely created so we rebuild the model
		if (!group || !groupInModel) {
			this._createTabsModel();
			return;
		}
		const tabs = this._groupLookup.get(groupId)?.tabs;
		if (!tabs) {
			return;
		}
		// Splice tab into group at index editorIndex
		const tabObject = this._buildTabObject(group, editorInput, editorIndex);
		tabs.splice(editorIndex, 0, tabObject);
		// Update lookup
		this._tabInfoLookup.set(this._generateTabId(editorInput, groupId), { group, editorInput, tab: tabObject });

		this._proxy.$acceptTabOperation({
			groupId,
			index: editorIndex,
			tabDto: tabObject,
			kind: TabModelOperationKind.TAB_OPEN
		});
	}