Drilling into a Library folder only ever swapped #library-groups's
contents via fetch, never touching browser history - so back had
nothing of the app's own to step through once you were a few folders
deep, and fell straight through to exiting the app instead of going up
a level.
Push a history entry per drill-down and breadcrumb jump, and restore
libraryTrail/re-fetch that level on popstate, so back now un-drills
one folder at a time and only reaches the app's actual exit once
you're back at the library root.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
rmsitzandClaude Sonnet 5
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