drop redo entries when writing new snapshots into history (microsoft#251299)

* drop redo entries when writing new snapshots into history

* undo unwanted changes

Author: amunger

src/vs/workbench/contrib/chat/browser/chatEditing/chatEditingSession.ts

@@ -420,7 +420,10 @@ export class ChatEditingSession extends Disposable implements IChatEditingSessio
 		const linearHistoryPtr = this._linearHistoryIndex.get();
 		const newLinearHistory: IChatEditingSessionSnapshot[] = [];
 		for (const entry of this._linearHistory.get()) {
-			if (linearHistoryPtr - entry.startIndex < entry.stops.length) {
+			if (entry.startIndex >= linearHistoryPtr) {
+				// all further entries are being dropped
+				break;
+			} else if (linearHistoryPtr - entry.startIndex < entry.stops.length) {
 				newLinearHistory.push({ requestId: entry.requestId, stops: entry.stops.slice(0, linearHistoryPtr - entry.startIndex), startIndex: entry.startIndex, postEdit: undefined });
 			} else {
 				newLinearHistory.push(entry);