Two holes left by the last change. A frame is opened with `window.location.href`
rather than a link, so the studio was still handed a fresh page and the scan with
it — every route out of the catalogue now goes through `go()`, which pushes the
address instead of reloading while a scan is in flight. And a row counted what was
filed away rather than what had been read, so it sat at zero for the whole of a
first scan: the catalogue's frames only reach IndexedDB in one batch at the end.
`ScanProgress.counts` carries the frames the scan has reached, per row, off the
scan's own bookkeeping, and the column reads it while the scan runs — the row
under the reader's eye moves as the roll is read, and the toolbar's line stays the
whole picture. A re-read counts from the start, which is what it is doing.
The regression check grows the two: a frame opened mid-scan from the catalogue
(of a roll it already holds) has to stay in the page, and the row has to count.
The catalogue hands the visitor to the studio with a plain `<a href>`, and the
app has no router: following it threw the page away, so a scan that was halfway
through a roll died with it. A scan belongs to the tab, not to the screen that
started it.
The scan now lives outside the component (`scanSession`/`startScan`/`stopScan`,
watched by whoever is up), so the catalogue can unmount and come back to a
reading that never stopped; a screen that returns joins it and sees the toolbar
line, the stop button and the rows filling in. The internal links are taken over
for a history push *only while a scan is in flight* — everywhere else the
browser navigates exactly as before, so the landing-to-studio flow is untouched.
`scripts/scan-nav-check.mjs` is the regression: a roll read one frame at a time
off a slow server, handed to the studio mid-scan, back to the catalogue, and the
whole roll read to the end with the studio up, counting documents along the way.
3dtours