The Xcode/App Store target (project.yml) was missing the CGMSynth C core (gm_synth.c, symlinked from fedac/native/src) that Package.swift declares and MenuBandGMSynth.swift imports — so 'xcodegen generate && xcodebuild' failed with 'unable to resolve module dependency: CGMSynth'. Compile gm_synth.c into the app target and expose its module map via SWIFT_INCLUDE_PATHS/HEADER_SEARCH_PATHS. Verified: xcodebuild Release (unsigned) now BUILD SUCCEEDED, default.metallib emitted. Also needed Metal toolchain (xcodebuild -downloadComponent MetalToolchain). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>