One home per fact: cut the copied rationale, and give the seam test room to mean something

src/ui/shell.test.ts

@@ -101,9 +101,8 @@ test("app shell can disable the menu: no sidebar, focused single-column layout",
 });
 
 test("app shell: fill is opt-in and composes with menu:false; what the class does is pinned in e2e", async () => {
-  // The opt-out from document scrolling is the shell's to give — a page cannot derive the height
-  // without knowing the topbar's own (AGENTS.md → UI). Its effect depends on the page's own flex
-  // chain, so full-flow holds that; this holds only that nothing opts a page in by accident.
+  // What the class does depends on the page's own flex chain (AGENTS.md → UI), so full-flow holds
+  // that; this holds only that nothing opts a page in by accident.
   const filled = await render({ fill: true, title: "Board", body: "<div>x</div>", nav: "" });
   assert.match(filled, /<div class="app app-fill">/);
   const bothOff = await render({ fill: true, menu: false, title: "Board", body: "<div>x</div>", nav: "" });