Long expeditions D1-c: T3 zones to new 22-26 room band

Both T3 zones follow the D1-a/b pattern: extend the graph so the longest
entry→boss walk lands in band, keep the zone's authored topology intact.

  manor_blackspire (T3): 11 → 35 nodes, longest 23 (band 22-26)
  underforge       (T3): 10 → 31 nodes, longest 23 (band 22-26)

Topology preserved per zone:
- Manor: two-stacked-3-way forks identity + full lock-kind coverage
  (LockNone, LockPerception, LockStatCheck, LockLevelMin). Adds the
  missing Trap anchor (Cursed Threshold). All six spokes are 3 mid-nodes
  so route choice is loot/encounter character, not shortcut economics.
- Underforge: one-way-descent gauntlet identity preserved — 17-node
  linear preamble through the existing Cooling River (TRAP) and Magma
  Chamber (ELITE), single 3-way antechamber fork before boss. All three
  antechamber spokes are 4 mid-nodes.

MinRooms/MaxRooms re-pitched 7-9 → 22-26 so the dice fallback also lands
in band for any future graphless variant.

internal/plugin/zone_graph_manor_blackspire_test.go

@@ -10,8 +10,10 @@ func TestManorBlackspireGraph_Registered(t *testing.T) {
 	if g.Entry != "manor_blackspire.entry" {
 		t.Errorf("entry node = %q", g.Entry)
 	}
-	if len(g.Nodes) != 11 {
-		t.Errorf("nodes = %d, want 11", len(g.Nodes))
+	// Long-expedition D1-c widened this zone from 11 → 35 nodes so the
+	// longest entry→boss walk lands in the T3 [22,26] traversal band.
+	if len(g.Nodes) != 35 {
+		t.Errorf("nodes = %d, want 35", len(g.Nodes))
 	}
 }
 
@@ -33,12 +35,14 @@ func TestManorBlackspireGraph_TwoStackedThreeWayForks(t *testing.T) {
 func TestManorBlackspireGraph_AllSpokesReachBoss(t *testing.T) {
 	g := zoneManorBlackspireGraph()
 	for _, leaf := range []string{
-		"manor_blackspire.master_bedroom",
-		"manor_blackspire.tower_observatory",
-		"manor_blackspire.hidden_oratory",
+		// great_hall spokes (entry of each 3-node branch).
 		"manor_blackspire.portrait_gallery",
-		"manor_blackspire.study",
-		"manor_blackspire.library",
+		"manor_blackspire.locked_study",
+		"manor_blackspire.forbidden_library",
+		// upper_hall spokes.
+		"manor_blackspire.master_bedroom",
+		"manor_blackspire.hidden_oratory",
+		"manor_blackspire.tower_observatory",
 	} {
 		if !reachable(g, leaf, "manor_blackspire.boss") {
 			t.Errorf("%s unreachable to boss", leaf)
@@ -46,9 +50,9 @@ func TestManorBlackspireGraph_AllSpokesReachBoss(t *testing.T) {
 	}
 }
 
-// TestManorBlackspireGraph_LockLevelMinFirstUse verifies this zone is
-// the first to author LockLevelMin, completing lock-kind coverage
-// (Perception, StatCheck, LevelMin, LockNone) by G8d.
+// TestManorBlackspireGraph_LockLevelMinFirstUse verifies the tower spoke
+// still carries the LockLevelMin gate so all four lock kinds (None,
+// Perception, StatCheck, LevelMin) remain authored within this zone.
 func TestManorBlackspireGraph_LockLevelMinFirstUse(t *testing.T) {
 	g := zoneManorBlackspireGraph()
 	var levelMinEdge *ZoneEdge
@@ -69,3 +73,29 @@ func TestManorBlackspireGraph_LockLevelMinFirstUse(t *testing.T) {
 		t.Error("level-gated edge missing hint")
 	}
 }
+
+// TestManorBlackspireGraph_SymmetricBranches locks in the D1-c design
+// intent: all six fork spokes are 3 mid-nodes long so any route walks
+// the same 23-room length — the choice is loot/encounter, not shortcut.
+func TestManorBlackspireGraph_SymmetricBranches(t *testing.T) {
+	g := zoneManorBlackspireGraph()
+	checks := []struct {
+		from, to, via string
+		want          int
+	}{
+		// great_hall → second_floor_landing, hops via each spoke.
+		{"manor_blackspire.great_hall", "manor_blackspire.second_floor_landing", "manor_blackspire.portrait_gallery", 4},
+		{"manor_blackspire.great_hall", "manor_blackspire.second_floor_landing", "manor_blackspire.locked_study", 4},
+		{"manor_blackspire.great_hall", "manor_blackspire.second_floor_landing", "manor_blackspire.forbidden_library", 4},
+		// upper_hall → spire_corridor, hops via each spoke.
+		{"manor_blackspire.upper_hall", "manor_blackspire.spire_corridor", "manor_blackspire.master_bedroom", 4},
+		{"manor_blackspire.upper_hall", "manor_blackspire.spire_corridor", "manor_blackspire.hidden_oratory", 4},
+		{"manor_blackspire.upper_hall", "manor_blackspire.spire_corridor", "manor_blackspire.tower_observatory", 4},
+	}
+	for _, c := range checks {
+		got := bfsHops(g, c.from, c.to, c.via)
+		if got != c.want {
+			t.Errorf("hops %s → %s via %s = %d, want %d", c.from, c.to, c.via, got, c.want)
+		}
+	}
+}