A fetch method that uses a parameter pack to fetch one or more PersistentModel types then runs a closure to return a Sendable result.

ModelContext+extension.swift

import SwiftData

extension ModelContext {
    /// FetchDescriptor is Sendable but inside a parameter pack there are sometimes issues with this working in Swift 6.0
    func fetch<each T: PersistentModel, Result: Sendable>(
        _ descriptor: repeat FetchDescriptor<each T>,
        with closure: @escaping @Sendable (repeat [each T]) throws -> Result
    ) throws -> Result {
        try closure(repeat try fetch(each descriptor))
    }
    
    /// An option with a pack of closures that return FetchDescriptors
    func fetch<each T: PersistentModel, Result: Sendable>(
        _ descriptor: repeat @escaping @Sendable() -> FetchDescriptor<each T>,
        with closure: @escaping @Sendable (repeat [each T]) throws -> Result
    ) throws -> Result {
        try closure(repeat try fetch((each descriptor)()))
    }
    
    /// An option with a single closure that returns a Tuple parameter pack of FetchDescriptor
    func fetch<each T: PersistentModel, Result: Sendable>(
        _ descriptor: @escaping @Sendable () -> (repeat FetchDescriptor<each T>),
        with closure: @escaping @Sendable (repeat [each T]) throws -> Result
    ) throws -> Result {
        return try closure(repeat try fetch(each descriptor()))
    }
}