Cover byte reclamation: one guarded helper, file first, covers row last (#154)

backend/internal/latest/poller.go

@@ -158,8 +158,8 @@ func (p *Poller) storeCover(ctx context.Context, sr store.Series, sourceURL stri
 	// The forced write replaces whether or not a Cover exists, and the row
 	// then tells the three outcomes apart: a blank filled, identical artwork
 	// re-served — an honest no-op — or a replacement whose previous address
-	// is stranded: its bytes stay served under the covers table (ADR-0014),
-	// the row just no longer points at them.
+	// is stranded and reclaimed below. A failed reclaim is logged and the
+	// stranded bytes stay served until a later call reclaims them.
 	previous, current, err := p.Store.ReplaceSeriesCover(sr.Site, sr.SeriesID, sourceURL, bytes, contentType)
 	if err != nil {
 		log.Printf("latest poll %q: persist cover: %v", sr.Key(), err)
@@ -171,6 +171,9 @@ func (p *Poller) storeCover(ctx context.Context, sr store.Series, sourceURL stri
 	case previous == current:
 		log.Printf("latest poll %q: cover unchanged, the site re-serves the same bytes", sr.Key())
 	default:
+		if err := p.Store.ReclaimCover(previous); err != nil {
+			log.Printf("latest poll %q: reclaim cover %s: %v", sr.Key(), previous, err)
+		}
 		log.Printf("latest poll %q: cover replaced %s -> %s", sr.Key(), previous, current)
 	}
 }