electron-builder (app-builder-lib 27.0.0-alpha.6) compiles a `.icon` given as
`mac.icon` into Contents/Resources/Assets.car and sets CFBundleIconName, but
only with actool >= 26 (Xcode 26); on any other host it throws and the build
fails. scripts/mac-icon.cjs picks the Icon Composer package when that actool
is present and the legacy .icns otherwise, so a dev Mac on Xcode 16 keeps
building the app it always built.
The release runners keep Xcode 16.4 selected although 26.x is installed, so
the darwin job now selects the newest Xcode 26 via DEVELOPER_DIR and asserts
the actool version before packaging; a silent fallback cannot ship from CI.
electron-builder's `.icon` path also replaces the bundled icon.icns with
actool's 256px fallback. macOS <= 15 shows that file, so after-pack restores
our 16..1024 assets/icon.icns.
26960b1afb