Mechanical cleanups, no behavior change:
- 15 copies of the same id-extraction loop collapse to slice.Map (5 repo
mocks, the scanner's track sweep, 4 wantIDs assertions) and slice.ToMap
(6 index-by-id loops in the hydration specs).
- disc.go built a map[string]bool purely to dedup folder ids and then
walked it back into a slice; slice.Unique says that directly.
- folders_artist.go's image filter is slice.Filter over model.IsImageFile.
- mock_artwork_repo deleted from a map while ranging it; maps.DeleteFunc
states the intent.
- sort.Slice -> slices.SortFunc + cmp.Or; math.Min/Max -> builtin min/max;
make+copy -> bytes.Clone; strings.Split -> SplitSeq on a per-request
path; three-clause pixel loops -> for range.
- Reuse utils.BaseName where a stem was recomputed by hand. Not at
playlist_cover.go:27: that path is a full OS path and utils.BaseName
uses path.Base, which does not split backslashes.
- Drop a dead nil-guard in agents.go: getAgent returns a bare nil
interface, and a type assertion on nil already yields ok == false.
cmp.Or was rejected for the gate fallback (func types are not comparable,
does not compile) and for ItemArtwork.AttemptedAt (cmp.Or compares
time.Time with ==, which includes loc; IsZero does not).
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