Build a local-first desktop utility that inventories ebook files, detects duplicates, repairs metadata, preserves folder and series organization, and creates a portable library archive with a human-readable manifest. Device-specific adapters would import and export supported reading positions, bookmarks, highlights, and settings where technically possible, while verification reports confirm that every source file reached the destination intact. Start with a guided migration between Android storage, Calibre libraries, and selected cloud folders rather than building another reading app.

Repeated Android storage-policy changes and reader-app regressions are breaking long-lived personal libraries, while readers increasingly use several phones, tablets, computers, and dedicated e-ink devices. The signals also show willingness to pay for reliable backup and synchronization, especially through one-time purchases rather than subscriptions.