src/vs/workbench/services/extensionManagement/electron-sandbox/extensionManagementService.ts/ExtensionManagementService/installVSIX
class ExtensionManagementService:	protected override async installVSIX(vsix: URI, server: IExtensionManagementServer, options: InstallVSIXOptions | undefined): Promise<ILocalExtension> {
		if (vsix.scheme === Schemas.vscodeRemote && server === this.extensionManagementServerService.localExtensionManagementServer) {
			const downloadedLocation = joinPath(this.environmentService.tmpDir, generateUuid());
			await this.downloadService.download(vsix, downloadedLocation);
			vsix = downloadedLocation;
		}
		const manifest = await this.getManifest(vsix);
		if (manifest) {
			await this.checkForWorkspaceTrust(manifest);
			return server.extensionManagementService.install(vsix, options);
		}

		return Promise.reject('Unable to get the extension manifest.');
	}