`--resize WxH@Hz` changes the output once the app is up and screenshots
after, so "it lands where a cold start at that size does" is a command
rather than a procedure. That check caught both of #16's defects and nothing
in `cargo test` can see it; it now passes byte for byte on `tabs` and `text`
for this branch.
Run one at a time: the rig reuses a single compositor and a single output,
so two invocations at once resize each other's window and quietly screenshot
the wrong thing.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>