Fix #openPullRequest to consider diff editors and use consistent terminology

Co-authored-by: alexr00 <38270282+alexr00@users.noreply.github.com>

Author: Copilot

src/lm/tools/openPullRequestTool.ts

@@ -12,10 +12,39 @@ export class OpenPullRequestTool extends PullRequestTool {
 	public static readonly toolId = 'github-pull-request_openPullRequest';
 
 	protected _findActivePullRequest(): PullRequestModel | undefined {
-		return PullRequestOverviewPanel.currentPanel?.getCurrentItem();
+		// First check if there's a PR overview panel open
+		const panelPR = PullRequestOverviewPanel.currentPanel?.getCurrentItem();
+		if (panelPR) {
+			return panelPR;
+		}
+
+		// If no overview panel is open, check if there's an active PR (checked out locally)
+		// This covers the case where users are viewing PR diffs without the overview panel
+		const folderManager = this.folderManagers.folderManagers.find((manager) => manager.activePullRequest);
+		return folderManager?.activePullRequest;
 	}
 
 	protected _confirmationTitle(): string {
 		return vscode.l10n.t('Open Pull Request');
 	}
+
+	override async prepareInvocation(): Promise<vscode.PreparedToolInvocation> {
+		const pullRequest = this._findActivePullRequest();
+		return {
+			pastTenseMessage: pullRequest ? vscode.l10n.t('Read pull request "{0}"', pullRequest.title) : vscode.l10n.t('No open pull request'),
+			invocationMessage: pullRequest ? vscode.l10n.t('Reading pull request "{0}"', pullRequest.title) : vscode.l10n.t('Reading open pull request'),
+			confirmationMessages: { title: this._confirmationTitle(), message: pullRequest ? vscode.l10n.t('Allow reading the details of "{0}"?', pullRequest.title) : vscode.l10n.t('Allow reading the details of the open pull request?') },
+		};
+	}
+
+	override async invoke(options: vscode.LanguageModelToolInvocationOptions<any>, token: vscode.CancellationToken): Promise<vscode.ExtendedLanguageModelToolResult | undefined> {
+		let pullRequest = this._findActivePullRequest();
+
+		if (!pullRequest) {
+			return new vscode.LanguageModelToolResult([new vscode.LanguageModelTextPart('There is no open pull request')]);
+		}
+
+		// Delegate to the base class for the actual implementation
+		return super.invoke(options, token);
+	}
 }