The FlutterMacOS.framework artifact is packaged as a zip that contains another zip.

FlutterMacOS.framework.zip

See example at https://storage.googleapis.com/flutter_infra_release/flutter/d1b9a6938ad77326ac3a94d92bbc77933ed829ed/darwin-x64-release/FlutterMacOS.framework.zip

Stop zipping FlutterMacOS.framework within the artifact zip. When complete, the zip should contain:

FlutterMacOS.framework

This requires an incremental step of shipping with both the FlutterMacOS.framework.zip and unzipped FlutterMacOS.framework in the same directory, which will double the size of the artifact from 11M to 22M. Having both will allow the tool and g3 roll to adopt the unzipped variant. Then, once adopted everywhere, delete the zip.

Tool changes (there may be more spots):

Roller changes:
https://source.corp.google.com/piper///depot/google3/mobile/flutter/tools/frob/roll_job/lib/src/cache_fetcher.dart;l=271-276?q=fluttermacos.framework&ss=piper%2FGoogle%2FPiper:google3%2Fmobile%2Fflutter%2Ftools%2F

https://source.corp.google.com/piper///depot/google3/mobile/flutter/tools/frob/roll_job/lib/src/cache_fetcher.dart;l=74-77?q=fluttermacos.framework&ss=piper%2FGoogle%2FPiper:google3%2Fmobile%2Fflutter%2Ftools%2F

This needs to be completed as part of #81855 per flutter/engine#35563.

See also where this was done for the Flutter.framework.zip to unzipped Flutter.xcframework:
Tool changes: #71495
Added unzip https://flutter-review.googlesource.com/c/recipes/+/9020
Related bug for roll script: b/issues/172736803#comment7
Removed zip https://flutter-review.googlesource.com/c/recipes/+/9560