Scroll restoration is a browser feature and it behaves like one — it survives a back button and almost nothing else. Close the tab, come back on Thursday from your phone, and a half-read book starts at chapter one.
The idea: treat position as content. Store chapter and percentage per entry, put "Continue reading" where a reader will actually meet it, and let the shelf show which spines have a ribbon in them.
Open questions:
- Does this belong to the device or to a person? Without accounts it can only be the device, and a device-scoped promise has to be phrased carefully or it reads as a broken one.
- What counts as finished? Ninety per cent scrolled, or the last chapter opened?
- Is a progress ring on a card encouraging, or does it turn reading into a metric?