feat(api): wire M6a routes; alpha artist list uses covers query

Replace handleListArtists alpha branch with ListArtistsAlphaWithCovers
(drops N+1 per-artist album lookup). Register /api/home and
/api/library/albums in api.go.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/api/api.go

@@ -46,11 +46,13 @@ func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playev
 			authed.Get("/artists/{id}/tracks", h.handleGetArtistTracks)
 			authed.Get("/albums/{id}", h.handleGetAlbum)
 			authed.Get("/albums/{id}/cover", h.handleGetCover)
+			authed.Get("/library/albums", h.handleListLibraryAlbums)
 			authed.Get("/tracks/{id}", h.handleGetTrack)
 			authed.Get("/tracks/{id}/stream", h.handleGetStream)
 			authed.Get("/search", h.handleSearch)
 			authed.Get("/radio", h.handleRadio)
 			authed.Get("/discover/suggestions", h.handleListSuggestions)
+			authed.Get("/home", h.handleGetHome)
 			authed.Post("/events", h.handleEvents)
 			authed.Post("/likes/tracks/{id}", h.handleLikeTrack)
 			authed.Delete("/likes/tracks/{id}", h.handleUnlikeTrack)

internal/api/library.go

@@ -184,8 +184,10 @@ func (h *handlers) handleGetArtistTracks(w http.ResponseWriter, r *http.Request)
 }
 
 // handleListArtists implements GET /api/artists with two sort modes
-// (alpha|newest) and enveloped pagination. album_count per artist is
-// computed via an N+1 — acceptable at limit=200.
+// (alpha|newest) and enveloped pagination. The alpha branch uses
+// ListArtistsAlphaWithCovers to ship cover_url + album_count in a
+// single query. The newest branch keeps its N+1 album_count lookup
+// (less hot path, no covers exposed).
 func (h *handlers) handleListArtists(w http.ResponseWriter, r *http.Request) {
 	sort := r.URL.Query().Get("sort")
 	if sort == "" {
@@ -200,45 +202,61 @@ func (h *handlers) handleListArtists(w http.ResponseWriter, r *http.Request) {
 		writeErr(w, http.StatusBadRequest, "bad_request", err.Error())
 		return
 	}
-
 	q := dbq.New(h.pool)
-	var artists []dbq.Artist
+
 	switch sort {
 	case "newest":
-		artists, err = q.ListArtistsNewest(r.Context(), dbq.ListArtistsNewestParams{
+		artists, err := q.ListArtistsNewest(r.Context(), dbq.ListArtistsNewestParams{
 			Limit: int32(limit), Offset: int32(offset),
 		})
-	default: // alpha
-		artists, err = q.ListArtistsAlpha(r.Context(), dbq.ListArtistsAlphaParams{
-			Limit: int32(limit), Offset: int32(offset),
-		})
-	}
-	if err != nil {
-		h.logger.Error("api: list artists failed", "err", err)
-		writeErr(w, http.StatusInternalServerError, "server_error", "lookup failed")
-		return
-	}
-	total, err := q.CountArtists(r.Context())
-	if err != nil {
-		h.logger.Error("api: count artists failed", "err", err)
-		writeErr(w, http.StatusInternalServerError, "server_error", "count failed")
-		return
-	}
-
-	items := make([]ArtistRef, 0, len(artists))
-	for _, a := range artists {
-		albums, aerr := q.ListAlbumsByArtist(r.Context(), a.ID)
-		if aerr != nil {
-			h.logger.Error("api: list albums for artist failed", "err", aerr)
+		if err != nil {
+			h.logger.Error("api: list artists newest", "err", err)
 			writeErr(w, http.StatusInternalServerError, "server_error", "lookup failed")
 			return
 		}
-		items = append(items, artistRefFrom(a, len(albums)))
+		total, terr := q.CountArtists(r.Context())
+		if terr != nil {
+			h.logger.Error("api: count artists", "err", terr)
+			writeErr(w, http.StatusInternalServerError, "server_error", "count failed")
+			return
+		}
+		items := make([]ArtistRef, 0, len(artists))
+		for _, a := range artists {
+			albums, aerr := q.ListAlbumsByArtist(r.Context(), a.ID)
+			if aerr != nil {
+				h.logger.Error("api: list albums for artist", "err", aerr)
+				writeErr(w, http.StatusInternalServerError, "server_error", "lookup failed")
+				return
+			}
+			items = append(items, artistRefFrom(a, len(albums)))
+		}
+		writeJSON(w, http.StatusOK, Page[ArtistRef]{
+			Items: items, Total: int(total), Limit: limit, Offset: offset,
+		})
+		return
+
+	default: // alpha
+		rows, err := q.ListArtistsAlphaWithCovers(r.Context(), dbq.ListArtistsAlphaWithCoversParams{
+			Limit: int32(limit), Offset: int32(offset),
+		})
+		if err != nil {
+			h.logger.Error("api: list artists alpha", "err", err)
+			writeErr(w, http.StatusInternalServerError, "server_error", "lookup failed")
+			return
+		}
+		total, terr := q.CountArtists(r.Context())
+		if terr != nil {
+			h.logger.Error("api: count artists", "err", terr)
+			writeErr(w, http.StatusInternalServerError, "server_error", "count failed")
+			return
+		}
+		items := make([]ArtistRef, 0, len(rows))
+		for _, row := range rows {
+			items = append(items, artistRefFromCovered(row.Artist, int(row.AlbumCount), row.CoverAlbumID))
+		}
+		writeJSON(w, http.StatusOK, Page[ArtistRef]{
+			Items: items, Total: int(total), Limit: limit, Offset: offset,
+		})
+		return
 	}
-	writeJSON(w, http.StatusOK, Page[ArtistRef]{
-		Items:  items,
-		Total:  int(total),
-		Limit:  limit,
-		Offset: offset,
-	})
 }