Since updating to macOS 26.4 I haven't been able to build my small project using Xcode 26.3, as all of my macros are broken with a "malformed response" error similar to this:
External macro implementation type 'ComposableArchitectureMacros.ReducerMacro' could not be found for macro 'Reducer()'; ComposableArchitectureMacros' produced malformed response
This is similar to issue reported in Swift Macro linker failures on Linux, and when building with xcodebuild but in that case it was using xcodebuild, which commonly produces this error when passing -sdk iOS (how you're supposed to disambiguate SDKs and use macros, I don't know), but seeing it through Xcode directly is apparently pretty rare, as I haven't found any other work arounds. This feels like it might be something with the prebuilts, but they actually didn't install after I cleared the cache, so I don't think that's the issue.
Any ideas?