fix(gen): prioritize tree generator over planar for acyclic graphs

When both planar and acyclic constraints specified, the tree generator
must take precedence. Tree constraint (m = n-1) is stricter than planar
(m ≤ 3n-6).

Changes:
- Skip planar generation when cycles.kind === 'acyclic'
- Trees are always planar, so fall through to Phase 1 tree generator

Author: Mearman

src/generation/generators/edge-generator.ts

@@ -351,11 +351,20 @@ const generateBaseStructure = (nodes: TestNode[], spec: GraphSpec, _config: Grap
 		return edges;
 	}
 
-	if (spec.planar?.kind === "planar") {
+	// Only use planar generator if not also constrained to be acyclic (tree)
+	// Tree constraint (m = n-1) is stricter than planar (m ≤ 3n-6)
+	if (spec.planar?.kind === "planar" && spec.cycles.kind !== "acyclic") {
 		generatePlanarEdges(nodes, edges, spec, rng);
 		return edges;
 	}
 
+	// Handle planar + acyclic combination by using tree generator
+	// Trees are always planar, so we defer to the tree generator from Phase 1
+	if (spec.planar?.kind === "planar" && spec.cycles.kind === "acyclic") {
+		// Skip planar generation - let Phase 1 tree generator handle it
+		// Fall through to default generation
+	}
+
 	if (spec.hamiltonian?.kind === "hamiltonian") {
 		generateHamiltonianEdges(nodes, edges, spec, rng);
 		return edges;