PR #4887 directly implements MONO_VMSB (as MVMSB/MONO_VMSB) in extmod/modframebuf.c — exactly the feature requested in issue #6303. The PR modifies the same file, adds the missing constant, and reverses the bit offset calculation to support MSB vertical ordering. The match is precise. Classification is LIKELY_DUPLICATE rather than DUPLICATE because merge status cannot be confirmed from the provided data.
Suggested action
If PR #4887 has been merged, close issue #6303 as resolved by it. If the PR is still open, link it to the issue as the implementing PR and track together.