fix(catalog): cap each facet query at 1000 distinct values

/api/v1/catalog/filters returned an 11.7 MB payload on this server's
audiobook library — 88k authors, 92k narrators, 161k series — and that
landed in every client filter-sheet open. Above ~1000 entries a
dropdown is unusable anyway, so cap each facet helper at
catalogFacetMaxValues (1000) with a SQL LIMIT.

Applied uniformly to listDistinctArrayColumnWithSource (genres,
studios, networks, countries), listDistinctScalarColumnWithSource
(content_rating, original_language), listDistinctPeopleByKindWithSource
(authors, narrators), listDistinctAudiobookSeriesWithSource, and
listDistinctJSONBLanguageWithSource (audio + subtitle languages, both
array and JSONB paths). Genres, studios, etc. have fewer than 1000
distinct values today, so the cap is a no-op for the small facets and
the visible effect lands on authors / narrators / series.

Stopgap, not the final answer. A real fix is server-side typeahead
where the request includes a search prefix and the response is the top
N matches for that prefix; tracked in a follow-up plan rather than
shipped here so existing audiobookshelf clients and the silo UI keep
working unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/catalog/browse.go

@@ -523,7 +523,8 @@ func listDistinctArrayColumnWithSource(
 		) vals
 		WHERE val <> ''
 		ORDER BY val ASC
-	`, column, fromClause, whereClause)
+		LIMIT %d
+	`, column, fromClause, whereClause, catalogFacetMaxValues)
 
 	rows, err := pool.Query(ctx, query, args...)
 	if err != nil {
@@ -576,7 +577,8 @@ func listDistinctScalarColumnWithSource(
 		%s
 		  AND mi.%s <> ''
 		ORDER BY mi.%s ASC
-	`, column, fromClause, whereClause, column, column)
+		LIMIT %d
+	`, column, fromClause, whereClause, column, column, catalogFacetMaxValues)
 
 	// When there are no WHERE conditions, the extra AND is invalid — prepend WHERE instead.
 	if whereClause == "" {
@@ -585,7 +587,8 @@ func listDistinctScalarColumnWithSource(
 			FROM %s
 			WHERE mi.%s <> ''
 			ORDER BY mi.%s ASC
-		`, column, fromClause, column, column)
+			LIMIT %d
+		`, column, fromClause, column, column, catalogFacetMaxValues)
 	}
 
 	rows, err := pool.Query(ctx, query, args...)
@@ -756,7 +759,8 @@ func listDistinctPeopleByKindWithSource(
 		  AND p.name IS NOT NULL
 		  AND BTRIM(p.name) <> ''
 		ORDER BY p.name ASC
-	`, fromClause, kindIdx, browseFilterPrefix(whereClause))
+		LIMIT %d
+	`, fromClause, kindIdx, browseFilterPrefix(whereClause), catalogFacetMaxValues)
 	return queryDistinctStrings(ctx, pool, query, args)
 }
 
@@ -791,7 +795,8 @@ func listDistinctAudiobookSeriesWithSource(
 			  AND BTRIM(s.series_name) <> ''
 		) names
 		ORDER BY LOWER(name) ASC
-	`, fromClause, browseFilterPrefix(whereClause))
+		LIMIT %d
+	`, fromClause, browseFilterPrefix(whereClause), catalogFacetMaxValues)
 	return queryDistinctStrings(ctx, pool, query, args)
 }
 
@@ -825,7 +830,8 @@ func listDistinctJSONBLanguageWithSource(
 			  AND lang IS NOT NULL
 			  AND lang <> ''
 			ORDER BY value ASC
-		`, fromClause, mediaFileJoin, arrayColumn, browseFilterPrefix(whereClause))
+			LIMIT %d
+		`, fromClause, mediaFileJoin, arrayColumn, browseFilterPrefix(whereClause), catalogFacetMaxValues)
 		return queryDistinctStrings(ctx, pool, query, args)
 	}
 
@@ -838,7 +844,8 @@ func listDistinctJSONBLanguageWithSource(
 		  AND mf.missing_since IS NULL
 		  AND COALESCE(track->>'language', '') <> ''
 		ORDER BY value ASC
-	`, fromClause, mediaFileJoin, column, browseFilterPrefix(whereClause))
+		LIMIT %d
+	`, fromClause, mediaFileJoin, column, browseFilterPrefix(whereClause), catalogFacetMaxValues)
 	return queryDistinctStrings(ctx, pool, query, args)
 }
 

internal/catalog/catalog_resolver.go

@@ -690,6 +690,16 @@ func (r *CatalogResolver) ListFiltersWithOptions(ctx context.Context, req Catalo
 // headroom for other concurrent work and avoids saturating the pool.
 const catalogFacetConcurrency = 6
 
+// catalogFacetMaxValues caps how many distinct values each facet query
+// returns. Above ~1000 entries a typeahead UI is the only sensible way to
+// present a dropdown — and the audiobook library on this server has
+// >88k distinct authors / >92k narrators / >161k series, which produced
+// an 11.7 MB /api/v1/catalog/filters response before this cap landed.
+// The SearchableSelect dropdown stays responsive at 1000 client-side
+// entries; beyond that, the filter response should switch to a server-
+// side typeahead surface (out of scope for the cap-only fix).
+const catalogFacetMaxValues = 1000
+
 func (r *CatalogResolver) listFiltersForSource(
 	ctx context.Context,
 	filters BrowseFilters,