The regions poster wall was downloading a .webp. UPG-100 opens a print dialog
over the page, and the Driver asked for the same UX with no difference.
This is one prop, not a second implementation: PosterWall's posterAction
defaults to 'download', UPG-100 passes "print", and regions passed nothing.
deliverPoster() branches on it and routes both the shipped-.webp and the
browser-rasterised path through the shared openPrintFrame, so the two walls
now print through exactly the same code.
The probe that covered this had been asserting the wrong thing. Its own
header said the Driver asked for print, but the assertion accepted "delivers
a file or says why" and then checked the file was a .webp — which a download
satisfies. It now asserts nothing is downloaded and that the shared print
frame is created.
Catching that took two attempts, because the frame is transient by design:
print() returns immediately in headless, afterprint fires, and the frame
removes itself within milliseconds. Polling the DOM afterwards found nothing
and looked like a broken print path. Subscribing to frameattached before the
click observes it without racing the cleanup.
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