Enforce tag specific drop validation (can't copy to the account level)

Frameworks/Account/Account.swift

@@ -167,6 +167,10 @@ public final class Account: DisplayNameProvider, UnreadCountProvider, Container,
         }
     }
     
+	public var usesTags: Bool {
+		return delegate.usesTags
+	}
+	
 	var refreshInProgress = false {
 		didSet {
 			if refreshInProgress != oldValue {

Frameworks/Account/AccountDelegate.swift

@@ -14,6 +14,7 @@ protocol AccountDelegate {
 
 	// Local account does not; some synced accounts might.
 	var supportsSubFolders: Bool { get }
+	var usesTags: Bool { get }
 	var opmlImportInProgress: Bool { get }
 	
 	var server: String? { get }

Frameworks/Account/Feedbin/FeedbinAccountDelegate.swift

@@ -31,6 +31,7 @@ final class FeedbinAccountDelegate: AccountDelegate {
 	private var log = OSLog(subsystem: Bundle.main.bundleIdentifier!, category: "Feedbin")
 
 	let supportsSubFolders = false
+	let usesTags = true
 	let server: String? = "api.feedbin.com"
 	var opmlImportInProgress = false
 	

Frameworks/Account/LocalAccount/LocalAccountDelegate.swift

@@ -19,6 +19,7 @@ public enum LocalAccountDelegateError: String, Error {
 final class LocalAccountDelegate: AccountDelegate {
 	
 	let supportsSubFolders = false
+	let usesTags = false
 	let opmlImportInProgress = false
 	
 	let server: String? = nil

Mac/MainWindow/Sidebar/SidebarOutlineDataSource.swift

@@ -176,6 +176,9 @@ private extension SidebarOutlineDataSource {
 		if nodeHasChildRepresentingDraggedFeed(dropTargetNode, draggedFeed) {
 			return SidebarOutlineDataSource.dragOperationNone
 		}
+		if violatesTagSpecificBehavior(dropTargetNode, draggedFeed) {
+			return SidebarOutlineDataSource.dragOperationNone
+		}
 		let dragOperation: NSDragOperation = localFeedsDropOperation(dropTargetNode, Set([draggedFeed]))
 		if parentNode == dropTargetNode && index == NSOutlineViewDropOnItemIndex {
 			return dragOperation
@@ -195,6 +198,9 @@ private extension SidebarOutlineDataSource {
 		if nodeHasChildRepresentingAnyDraggedFeed(dropTargetNode, draggedFeeds) {
 			return SidebarOutlineDataSource.dragOperationNone
 		}
+		if violatesTagSpecificBehavior(dropTargetNode, draggedFeeds) {
+			return SidebarOutlineDataSource.dragOperationNone
+		}
 		if parentNode !== dropTargetNode || index != NSOutlineViewDropOnItemIndex {
 			outlineView.setDropItem(dropTargetNode, dropChildIndex: NSOutlineViewDropOnItemIndex)
 		}
@@ -483,6 +489,29 @@ private extension SidebarOutlineDataSource {
 		return false
 	}
 
+	func violatesTagSpecificBehavior(_ parentNode: Node, _ draggedFeed: PasteboardFeed) -> Bool {
+		return violatesTagSpecificBehavior(parentNode, Set([draggedFeed]))
+	}
+	
+	func violatesTagSpecificBehavior(_ parentNode: Node, _ draggedFeeds: Set<PasteboardFeed>) -> Bool {
+		guard let parentAccount = nodeAccount(parentNode), parentAccount.usesTags else {
+			return false
+		}
+		
+		for draggedFeed in draggedFeeds {
+			if parentAccount.accountID != draggedFeed.accountID {
+				return false
+			}
+		}
+		
+		// Can't copy to the account when using tags
+		if parentNode.representedObject is Account && (NSApplication.shared.currentEvent?.modifierFlags.contains(.option) ?? false) {
+			return true
+		}
+		
+		return false
+	}
+	
 	func indexWhereDraggedFeedWouldAppear(_ parentNode: Node, _ draggedFeed: PasteboardFeed) -> Int {
 		let draggedFeedWrapper = PasteboardFeedObjectWrapper(pasteboardFeed: draggedFeed)
 		let draggedFeedNode = Node(representedObject: draggedFeedWrapper, parent: nil)