Branching zones G8c: Sunken Temple sequential forks (no mid-path merge)

T2 zone, third authored graph. Shape: two-tier sequential forks where
each path is unique up to the boss room. Four committed leaves
(kuo_toa_pen / glyph_chamber / aboleth_thralls / coral_reliquary) all
terminate at the boss; no mid-path node has >1 incoming edge.

Differentiates from Crypt's diamond and Forest's asymmetric-diamond by
producing two parallel "Y" subtrees on the !zone map instead of a
converging branch. Exercises Perception + StatCheck (STR) + LockNone
in a single zone (covered by TestSunkenTempleGraph_LockKindCoverage).

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

internal/plugin/zone_graph_sunken_temple_test.go

@@ -0,0 +1,80 @@
+package plugin
+
+import "testing"
+
+func TestSunkenTempleGraph_Registered(t *testing.T) {
+	g, ok := zoneGraphRegistry[ZoneSunkenTemple]
+	if !ok {
+		t.Fatal("zoneSunkenTempleGraph not registered")
+	}
+	if g.Entry != "sunken_temple.entry" {
+		t.Errorf("entry node = %q", g.Entry)
+	}
+	if g.Boss != "sunken_temple.boss" {
+		t.Errorf("boss node = %q", g.Boss)
+	}
+	if len(g.Nodes) != 10 {
+		t.Errorf("nodes = %d, want 10", len(g.Nodes))
+	}
+}
+
+// TestSunkenTempleGraph_FourDistinctPaths verifies the four leaves
+// (kuo_toa_pen, glyph_chamber, aboleth_thralls, coral_reliquary) all
+// reach the boss. Together with the no-merge invariant below, this
+// confirms the design intent: four committed paths, not a diamond.
+func TestSunkenTempleGraph_FourDistinctPaths(t *testing.T) {
+	g := zoneSunkenTempleGraph()
+	for _, leaf := range []string{
+		"sunken_temple.kuo_toa_pen",
+		"sunken_temple.glyph_chamber",
+		"sunken_temple.aboleth_thralls",
+		"sunken_temple.coral_reliquary",
+	} {
+		if !reachable(g, leaf, "sunken_temple.boss") {
+			t.Errorf("%s unreachable to boss", leaf)
+		}
+	}
+}
+
+// TestSunkenTempleGraph_NoMidPathMerge ensures no node other than the
+// boss has more than one incoming edge. If a future edit collapses the
+// two subtrees into a converging diamond, this test fails — that's the
+// signal to either rename the zone's shape comment or re-author.
+func TestSunkenTempleGraph_NoMidPathMerge(t *testing.T) {
+	g := zoneSunkenTempleGraph()
+	incoming := map[string]int{}
+	for _, outs := range g.Edges {
+		for _, e := range outs {
+			incoming[e.To]++
+		}
+	}
+	for id, n := range g.Nodes {
+		if n.IsBoss {
+			continue
+		}
+		if incoming[id] > 1 {
+			t.Errorf("node %q has %d incoming edges, want ≤1 (no mid-path merge)", id, incoming[id])
+		}
+	}
+	// Boss intentionally has 4 incoming edges (one per leaf).
+	if incoming["sunken_temple.boss"] != 4 {
+		t.Errorf("boss incoming = %d, want 4", incoming["sunken_temple.boss"])
+	}
+}
+
+func TestSunkenTempleGraph_LockKindCoverage(t *testing.T) {
+	g := zoneSunkenTempleGraph()
+	kinds := map[ZoneEdgeLockKind]bool{}
+	for _, outs := range g.Edges {
+		for _, e := range outs {
+			kinds[e.Lock] = true
+		}
+	}
+	// Sunken Temple deliberately exercises Perception + StatCheck +
+	// LockNone in one zone.
+	for _, k := range []ZoneEdgeLockKind{LockNone, LockPerception, LockStatCheck} {
+		if !kinds[k] {
+			t.Errorf("missing lock kind %s — variety check", k)
+		}
+	}
+}