Preserve geometric float clearance endpoints

render-repros/checks.json

@@ -222,6 +222,11 @@
     {"name": "same-side floats remain adjacent", "color": "#1971c2", "x": 80, "y": 0, "width": 80, "height": 30},
     {"name": "trailing right float shares the band", "color": "#e8590c", "x": 340, "y": 0, "width": 60, "height": 30}
   ],
+  "nested-float-clearance": [
+    {"name": "earlier tall float keeps its full shared-BFC endpoint", "color": "#087f5b", "x": 0, "y": 0, "width": 120, "height": 100},
+    {"name": "later shorter descendant float shares the remaining band", "color": "#1971c2", "x": 120, "y": 20, "width": 200, "height": 50},
+    {"name": "clearfix advances following flow below the tallest float", "color": "#862e9c", "x": 0, "y": 100, "width": 600, "height": 20}
+  ],
   "modern-hydration-contracts": [
     {"name": "modern hydration contracts", "color": "#16803c", "width": 360, "height": 90}
   ],

render-repros/nested-float-clearance.html

@@ -0,0 +1,41 @@
+<!doctype html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>nested float clearance keeps the tallest shared-BFC endpoint</title>
+  <style>
+    html, body { margin: 0; }
+    .container { width: 600px; }
+    .header-float {
+      float: left;
+      width: 120px;
+      height: 100px;
+      background: #087f5b;
+    }
+    .collapse::after {
+      display: table;
+      clear: both;
+      content: "";
+    }
+    .nested-float {
+      float: left;
+      width: 200px;
+      height: 50px;
+      margin-top: 20px;
+      background: #1971c2;
+    }
+    .following {
+      width: 600px;
+      height: 20px;
+      background: #862e9c;
+    }
+  </style>
+</head>
+<body>
+  <div class="container">
+    <div class="header-float"></div>
+    <div class="collapse"><div class="nested-float"></div></div>
+    <div class="following"></div>
+  </div>
+</body>
+</html>