diff --git a/frontend/textbooks/algebra_8.html b/frontend/textbooks/algebra_8.html
index dc91c79..25a553f 100644
--- a/frontend/textbooks/algebra_8.html
+++ b/frontend/textbooks/algebra_8.html
@@ -504,8 +504,16 @@ function buildParaSelector(){
   });
 }
 
+const BUILT = new Set();
+const BUILDERS = { p1:()=>buildP1(), p2:()=>buildP2(), p3:()=>buildP3(), p4:()=>buildP4(), p5:()=>buildP5(), p6:()=>buildP6(), final:()=>buildFinal() };
+function ensureBuilt(id){
+  if(BUILT.has(id)) return;
+  const fn = BUILDERS[id];
+  if(fn){ fn(); BUILT.add(id); }
+}
 function goTo(id){
   STATE.current = id;
+  ensureBuilt(id);
   document.querySelectorAll('.sec').forEach(s=>s.classList.remove('active'));
   const el = document.getElementById('sec-' + id);
   if(el) el.classList.add('active');
@@ -734,16 +742,8 @@ function init(){
   initTheme();
   initSearch();
   buildParaSelector();
-  // Build all paragraph bodies
-  if(typeof buildP1 === 'function') buildP1();
-  if(typeof buildP2 === 'function') buildP2();
-  if(typeof buildP3 === 'function') buildP3();
-  if(typeof buildP4 === 'function') buildP4();
-  if(typeof buildP5 === 'function') buildP5();
-  if(typeof buildP6 === 'function') buildP6();
-  if(typeof buildFinal === 'function') buildFinal();
   refreshProgressUI();
-  goTo('p1');
+  goTo('p1');                            // строит только §1, остальные — лениво при переходе
   setTimeout(()=>achievement('start','Начало пути по корням!'), 800);
 }