Reuse chat editor count in name (microsoft#186799)

Fix microsoft/vscode-copilot#149

Author: roblourens

src/vs/workbench/contrib/chat/browser/chatEditorInput.ts

@@ -5,7 +5,7 @@
 
 import { CancellationToken } from 'vs/base/common/cancellation';
 import { Emitter } from 'vs/base/common/event';
-import { Disposable } from 'vs/base/common/lifecycle';
+import { Disposable, toDisposable } from 'vs/base/common/lifecycle';
 import { Schemas } from 'vs/base/common/network';
 import { URI } from 'vs/base/common/uri';
 import * as nls from 'vs/nls';
@@ -18,9 +18,10 @@ import { IChatModel } from 'vs/workbench/contrib/chat/common/chatModel';
 import { IChatService } from 'vs/workbench/contrib/chat/common/chatService';
 
 export class ChatEditorInput extends EditorInput {
+	static readonly countsInUse = new Set<number>();
+
 	static readonly TypeID: string = 'workbench.input.chatSession';
 	static readonly EditorID: string = 'workbench.editor.chatSession';
-	static count = 0;
 
 	private readonly inputCount: number;
 	public sessionId: string | undefined;
@@ -33,6 +34,15 @@ export class ChatEditorInput extends EditorInput {
 		return ChatUri.generate(handle);
 	}
 
+	static getNextCount(): number {
+		let count = 0;
+		while (ChatEditorInput.countsInUse.has(count)) {
+			count++;
+		}
+
+		return count;
+	}
+
 	constructor(
 		readonly resource: URI,
 		readonly options: IChatEditorOptions,
@@ -47,7 +57,9 @@ export class ChatEditorInput extends EditorInput {
 
 		this.sessionId = 'sessionId' in options.target ? options.target.sessionId : undefined;
 		this.providerId = 'providerId' in options.target ? options.target.providerId : undefined;
-		this.inputCount = ChatEditorInput.count++;
+		this.inputCount = ChatEditorInput.getNextCount();
+		ChatEditorInput.countsInUse.add(this.inputCount);
+		this._register(toDisposable(() => ChatEditorInput.countsInUse.delete(this.inputCount)));
 	}
 
 	override get editorId(): string | undefined {