fix: restore chat attachments when cycling through chat input history (microsoft#223782)

* fix: save chat attachments for chat history before clearing them

* fix: avoid firing change event if no attachments were removed

* fix: don't clear existing attachments when appending new ones

Author: joyceerhl

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

@@ -348,18 +348,20 @@ export class ChatInputPart extends Disposable implements IHistoryNavigationWidge
 	}
 
 	attachContext(overwrite: boolean, ...contentReferences: IChatRequestVariableEntry[]): void {
-		const removed = Array.from(this._attachedContext);
+		const removed = [];
 		if (overwrite) {
+			removed.push(...Array.from(this._attachedContext));
 			this._attachedContext.clear();
 		}
 
 		if (contentReferences.length > 0) {
 			for (const reference of contentReferences) {
 				this._attachedContext.add(reference);
 			}
-			this.initAttachedContext(this.attachedContextContainer);
 		}
+
 		if (removed.length > 0 || contentReferences.length > 0) {
+			this.initAttachedContext(this.attachedContextContainer);
 			this._onDidChangeContext.fire({ removed, added: contentReferences });
 		}
 	}

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

@@ -786,10 +786,10 @@ export class ChatWidget extends Disposable implements IChatWidget {
 			});
 
 			if (result) {
-				this.inputPart.clearContext();
 				this.inputPart.acceptInput(isUserQuery);
 				this._onDidSubmitAgent.fire({ agent: result.agent, slashCommand: result.slashCommand });
 				this.inputPart.updateState(this.collectInputState());
+				this.inputPart.clearContext();
 				result.responseCompletePromise.then(() => {
 					const responses = this.viewModel?.getItems().filter(isResponseVM);
 					const lastResponse = responses?.[responses.length - 1];

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

@@ -70,8 +70,10 @@ export class ChatContextAttachments extends Disposable implements IChatWidgetCon
 	}
 
 	private _removeContext(attachments: IChatRequestVariableEntry[]) {
-		attachments.forEach(this._attachedContext.delete, this._attachedContext);
-		this._onDidChangeInputState.fire();
+		if (attachments.length) {
+			attachments.forEach(this._attachedContext.delete, this._attachedContext);
+			this._onDidChangeInputState.fire();
+		}
 	}
 
 	private _clearAttachedContext() {