swift scripts run in the background with swift launched via swiftly will make the current shell exit

## Steps to Reproduce - Create a file `yolo.swift` that contains the following content: ```swift #!/usr/bin/env swift print("hello") ``` - Make it executable - Run it like so with `swiftly` properly installed and in the `PATH`: ```bash ./yolo.swift & ``` ## Expected Behavior The script should run in the background, output `hello` and then exit, and the shell should stay alive. ## Actual Behavior The script launches in the background, but zsh errors out reading the TTY and exits: ```text prompt) ./toto.swift & [1] 64386 prompt) zsh: error on TTY read: Input/output error zsh: warning: 1 jobs SIGHUPed [1] + hangup ./toto.swift prompt) Saving session... ...copying shared history... ...saving history...truncating history files... ...completed. [Process completed] ``` ## Environment - macOS 26.2 (25C56) - Terminal 2.15 (466) - zsh 5.9 (arm64-apple-darwin25.0) - swiftly 1.1.1 - swift from Xcode: ```text swift-driver version: 1.127.14.1 Apple Swift version 6.2 (swiftlang-6.2.3.3.20 clang-1700.6.3.2) Target: arm64-apple-macosx26.0 ``` ## My Analysis I’m not 100% sure that’s the problem, but I’m pretty sure the issue actually comes from [swift-subprocess](<https://github.com/swiftlang/swift-subprocess>). I actually had this exact same issue with [my own “subprocess” implementation](<https://github.com/xcode-actions/swift-process-invocation>) (I really should write a Readme…). The [fix](<https://github.com/xcode-actions/swift-process-invocation/commit/382dc979de2b080920d8fdcc19705265ccf8eeb5#diff-b73f49f2c203aea220b84ffcec7bcc4e542a50838ad38524dc10a483b4957405R467-R471>) consisted in _not_ setting the current process group ID of the input file descriptor if the process was in the background (which I determined by checking whether the current process group ID of the file descriptor is my own process group ID).