fix: stabilize cold 2.5D first frame

Issue: #654
User-Visible: yes

scripts/render-layout-read.mjs

@@ -0,0 +1,45 @@
+#!/usr/bin/env node
+// #654: render and 2.5D pure helpers must not force browser layout. This is an
+// AST contract, not a regex anchor: formatting and comments cannot satisfy it.
+import { readFileSync, readdirSync } from 'node:fs';
+import ts from 'typescript';
+
+const forbidden = new Set(['getComputedStyle', 'getBoundingClientRect']);
+const source = (path) => ts.createSourceFile(
+  path, readFileSync(new URL(`../${path}`, import.meta.url), 'utf8'),
+  ts.ScriptTarget.Latest, true,
+);
+const callName = (node) => !ts.isCallExpression(node) ? null
+  : ts.isIdentifier(node.expression) ? node.expression.text
+    : ts.isPropertyAccessExpression(node.expression) ? node.expression.name.text : null;
+const forbiddenCalls = (node) => {
+  const found = [];
+  const visit = (child) => {
+    const name = callName(child);
+    if (name && forbidden.has(name)) found.push(name);
+    ts.forEachChild(child, visit);
+  };
+  visit(node);
+  return found;
+};
+
+const card = source('src/houseplan-card.ts');
+const required = new Set(['render', '_renderBody', 'willUpdate']);
+const checked = new Set();
+const visit = (node) => {
+  if (ts.isMethodDeclaration(node) && node.name && ts.isIdentifier(node.name)
+      && required.has(node.name.text)) {
+    checked.add(node.name.text);
+    const calls = forbiddenCalls(node.body);
+    if (calls.length) throw new Error(`${node.name.text} forces layout: ${calls.join(', ')}`);
+  }
+  ts.forEachChild(node, visit);
+};
+visit(card);
+if ([...required].some((name) => !checked.has(name))) throw new Error('guarded lifecycle method is missing');
+
+for (const file of readdirSync(new URL('../src', import.meta.url)).filter((name) => /^iso-.*\.ts$/.test(name))) {
+  const calls = forbiddenCalls(source(`src/${file}`));
+  if (calls.length) throw new Error(`${file} forces layout: ${calls.join(', ')}`);
+}
+console.log('render/layout-read AST contract: OK');