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dirs::data_dir() returns None on Android, which silently disabled every persistence path (settings, stats, achievements, replays, game-state, time-attack sessions, user themes). New solitaire_data::platform::data_dir() shim falls through to dirs::data_dir() on desktop and returns the per-app sandbox at /data/data/com.solitairequest.app/files on Android — no JNI needed, since the package id is pinned in [package.metadata.android]. CLAUDE.md §10 already flagged this as a known pitfall; the shim pays it down at the one chokepoint instead of per feature. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>