feat(home): land on Home, and make it worth landing on

The app opened on Tracks — an alphabetical list of everything, which is
the one entry point that is identical every time and therefore gives the
user nothing to start from. Home is listed first in the nav and is the
page built to answer 'what should I play' (H-8).

Two things had to be true before that was an improvement.

An album with no cover rendered as a small dim icon on a surface the
same colour as the page, so a shelf read as having holes in it, while
the Albums and Artists grids both drew a letter tile (H-9). It draws the
same tile now.

And a shelf that repeats the one above it is suppressed, the way an
empty one already is — 'On repeat' was 'Pick up where you left off'
reordered. The rule fires only when the shelf is not showing the whole
library: a repeat is a fault only if a different row was possible, and
measured against a fixed shelf size instead this let an 11-album library
keep three identical shelves while a 13-album one lost them.

The first two versions of that rule were wrong and the *existing* Go
tests caught both — it collapsed a four-album library to a single shelf.

Nine e2e specs assumed the app starts on Tracks and now navigate there,
and one new spec freezes the landing itself. Home's page-header action
is 'Shuffle suggestions': 'Shuffle' alone was two different controls
with one accessible name, which only became reachable together once a
cached Home was always in the tree.

backend/home/home.go

@@ -149,9 +149,24 @@ func (s *Service) GetShelves() ([]Shelf, error) {
 	shelves := make([]Shelf, 0, 8) //nolint:mnd // rough capacity hint
 
 	add := func(shelf Shelf, ok bool) {
-		if ok && len(shelf.Albums) > 0 {
-			shelves = append(shelves, shelf)
+		if !ok || len(shelf.Albums) == 0 {
+			return
 		}
+
+		// A repeat is only a fault if a different row was possible. A
+		// shelf showing the *entire* library answers every question with
+		// the same albums because there are no others, and suppressing
+		// those rows punishes a small library for being small — measured
+		// against a fixed shelf size instead, this let the fixture
+		// library keep three identical shelves while a library one album
+		// larger lost them.
+		if len(shelf.Albums) < len(albums) &&
+			len(shelves) > 0 &&
+			duplicates(shelf, shelves[len(shelves)-1]) {
+			return
+		}
+
+		shelves = append(shelves, shelf)
 	}
 
 	add(s.recentlyPlayed(ctx, byID))
@@ -169,6 +184,56 @@ func (s *Service) GetShelves() ([]Shelf, error) {
 	return shelves, nil
 }
 
+// duplicateThreshold is the share of a shelf that has to be in the
+// shelf above before the second one is not worth showing.  Two thirds:
+// one album in common between two rows of four is a coincidence, three
+// is the same row with a different heading.
+const duplicateThreshold = 2.0 / 3.0
+
+// duplicateMinimum is the shortest shelf this rule judges at all.
+//
+// Below it the ratio says nothing: two rows of one album overlap by
+// 100% whenever they agree at all.  The first version of this had no
+// floor and no library-size guard, and collapsed a four-album library
+// to a single shelf — caught by the existing tests, not by the one
+// written for the change.
+const duplicateMinimum = 3
+
+// duplicates reports whether a shelf is substantially the shelf above
+// it wearing a different reason.
+//
+// A small library has one signal, not six: everything recently played
+// is also everything most played is also everything recently added, so
+// "Pick up where you left off" and "On repeat" render the same four
+// covers in a different order and the page reads as repeating itself
+// (H-9).  This is the same rule as omitting an empty shelf, one step
+// further: a shelf has to be worth its own row.
+//
+// Only the shelf immediately above is compared, deliberately.  Two rows
+// that share content are only jarring when they are adjacent, and
+// comparing against everything already shown would delete the genre and
+// random shelves on any library small enough to reach this at all.
+func duplicates(shelf, previous Shelf) bool {
+	if len(shelf.Albums) < duplicateMinimum {
+		return false
+	}
+
+	above := make(map[int64]struct{}, len(previous.Albums))
+	for _, album := range previous.Albums {
+		above[album.ID] = struct{}{}
+	}
+
+	shared := 0
+
+	for _, album := range shelf.Albums {
+		if _, ok := above[album.ID]; ok {
+			shared++
+		}
+	}
+
+	return float64(shared)/float64(len(shelf.Albums)) >= duplicateThreshold
+}
+
 // resolve turns album ids into albums, dropping any the library no
 // longer has (a scan can remove an album between the two queries).
 func resolve(ids []int64, byID map[int64]library.Album) []library.Album {

backend/home/home_test.go

@@ -257,3 +257,82 @@ func TestGetShelvesSkipsAlbumsTheLibraryNoLongerHas(t *testing.T) {
 		}
 	}
 }
+
+// A shelf has to be worth its own row.
+//
+// A library with one signal answers several questions with the same
+// albums, so shelves render the same covers in different orders under
+// different reasons and the page reads as repeating itself (H-9).
+// Confirmed in the running app on the fixture library before this
+// existed: "On repeat" was "Pick up where you left off" reordered.
+//
+// The library has to be bigger than one shelf for the rule to apply at
+// all, which is the point: a repeat is only a fault if a different row
+// was possible.
+func TestGetShelvesOmitsAShelfThatRepeatsTheOneAboveIt(t *testing.T) {
+	db := database.NewTestDB(t)
+
+	albums := make([]library.Album, 0, 16)
+
+	// Four albums carry the whole play history, so "what you played
+	// last" and "what you play most" can only answer with those four.
+	for i := range 4 {
+		name := "Played " + string(rune('A'+i))
+		id := seed(t, db, name, "Solo", "", 50+i, "2026-08-1"+string(rune('0'+i))+" 00:00:00")
+
+		albums = append(albums, library.Album{ID: id, Name: name, ArtistName: "Solo"})
+	}
+
+	// …and ten more the user has never touched, so the library is
+	// larger than a single shelf and a different row was possible.
+	for i := range 10 {
+		name := "Quiet " + string(rune('A'+i))
+		id := seed(t, db, name, "Nobody", "", 0, "")
+
+		albums = append(albums, library.Album{ID: id, Name: name, ArtistName: "Nobody"})
+	}
+
+	svc := home.NewService(slog.Default(), db, fakeLibrary{albums: albums})
+
+	shelves, err := svc.GetShelves()
+	if err != nil {
+		t.Fatalf("GetShelves: %v", err)
+	}
+
+	// The first of a duplicate pair survives: the reason the user sees
+	// is the one that came first, not the one built last.
+	if !hasKind(shelves, home.KindRecentlyPlayed) {
+		t.Fatalf("expected a recently-played shelf, got %v", shelfKinds(shelves))
+	}
+
+	// And the page still has somewhere to start.
+	if len(shelves) < 2 {
+		t.Fatalf("suppression left %d shelves: %v", len(shelves), shelfKinds(shelves))
+	}
+
+	for i := 1; i < len(shelves); i++ {
+		above := shelves[i-1]
+		shared := 0
+
+		for _, a := range shelves[i].Albums {
+			for _, b := range above.Albums {
+				if a.ID == b.ID {
+					shared++
+
+					break
+				}
+			}
+		}
+
+		if len(shelves[i].Albums) < 3 {
+			continue
+		}
+
+		if ratio := float64(shared) / float64(len(shelves[i].Albums)); ratio >= 2.0/3.0 {
+			t.Errorf(
+				"shelf %q repeats %q (%d of %d albums)",
+				shelves[i].Kind, above.Kind, shared, len(shelves[i].Albums),
+			)
+		}
+	}
+}