Note: I rebuilt the pkg file using the .app bundle under /tmp because that's where the output of xar went. Additionally, the com.apple.security.app-sandbox key is set to true in the entitlement and plutil returns OK for that file. Thank you for your suggestions.

Additionally, I noticed the error refers to the com.apple.quarantine extended file attribute, not com.apple.macl that xattr returns, so I'm not sure where it is coming from.

security find-identity -v B9C100CC75910543E3FCD9AE63357AE4E2736723 "Apple Development: Harroll Dean Castle (76CZ7DC9QM)" D67F1D2EE9FC682B0BDAFDA1924936335C6E7595 "Apple Distribution: Chip Castle Dot Com, Inc. (BXN9N7MNU3)" D99EF2166A4F18DC4DA375C39F20F3DF2656E841 "3rd Party Mac Developer Installer: Chip Castle Dot Com, Inc. (BXN9N7MNU3)" 3 valid identities found

As suggested, I created a sample project in Xcode, which contains: macos-template.xcodeproj project.pbxproj project.xcworkspace contents.xcworkspacedata xcshareddata swiftpm configuration xcuserdata chip.xcuserdatad UserInterfaceState.xcuserstate xcuserdata chip.xcuserdatad xcschemes xcschememanagement.plist Apologies for formatting. This doesn't match "Placing content in a bundle". Is there a way to Export the structure? I tried to Archive, but that just prompts to Distribute/Validate. Thanks.

A lot of great info here - very much appreciated! I've read most of it over the last few weeks and kept running into issues, but I'll revisit it with the new macOS/Xcode combo I installed to see what progress I make. There are a lot of Ruby programmers that would like to build apps for macOS, and while I realize it's not a priority for Apple, I'm hoping to share my progress with them so they can focus on building cool things. I'll follow up here as I run into issues. Thanks again.

No worries, and thanks for the update. I upgraded to Sequoia and Xcode 16.2, so hopefully I can make progress with that combo.