Client: back up data/sounds in portable mode and mention it in the
warning; reuse a recent session only when complete and covering the
current sources (source manifest), estimate size only for fresh copies,
normalize dedup via isInsideDir.
Helper: source manifest per session with sessionCoversSources(), clear
out-params on all failure paths.
NSIS: document defensive portable branch, merge backup over surviving
data/ to repair partial deletes, copy (not move) wording in relocate,
note .txt exclusion in deck notice.
NSIS: clear stale %TEMP% backup and only arm restore when something was copied, directory-existence checks, back up loose .dec decks, drop downloaded pics but keep pics\CUSTOM.
Helper: single session dir per run (ms timestamps), same-basename disambiguation, partial copies still report their location.
