fix: address PR review feedback

- Exit non-zero on startup failures in render test runner (P1)
- Wait for browser-side runAllTests() completion before reading canvases (P2)
- Use || instead of ?? for font metric fallbacks so 0 triggers fallback (P2)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: slang25

demo/bin/render-test.ts

@@ -133,18 +133,9 @@ async function main() {
       timeout: 30000,
     });
 
-    // Wait for fonts to load - match the logic in render-test.html
-    await page.evaluate(async () => {
-      const fontVariants = [
-        '14px "JetBrainsMono NF"',
-        'bold 14px "JetBrainsMono NF"',
-        'italic 14px "JetBrainsMono NF"',
-        'bold italic 14px "JetBrainsMono NF"',
-      ];
-      await Promise.all(fontVariants.map(font => document.fonts.load(font)));
-      await document.fonts.ready;
-    });
-    await new Promise((r) => setTimeout(r, 500)); // Extra time for font rendering
+    // Wait for the page's runAllTests() to complete.
+    // render-test.html sets window.__testsComplete = true when done.
+    await page.waitForFunction('window.__testsComplete === true', { timeout: 60000 });
 
     // Get test cases from the page
     const testCases = await page.evaluate(() => {
@@ -288,4 +279,7 @@ function calculateDiffPercent(buf1: Buffer, buf2: Buffer): number {
   return (diffBytes / maxSize) * 100;
 }
 
-main().catch(console.error);
+main().catch((e) => {
+  console.error(e);
+  process.exit(1);
+});

demo/render-test.html

@@ -779,6 +779,7 @@ <h1>Visual Render Tests</h1>
       }
 
       document.getElementById('run-btn').disabled = false;
+      window.__testsComplete = true;
     }
 
     // Initialize

lib/renderer.ts

@@ -226,12 +226,12 @@ export class CanvasRenderer {
     // characters (U+E0B0, U+E0B6, etc.) which are designed to fill the full cell height.
     // Fall back to actual metrics if font metrics aren't available.
     const ascent =
-      widthMetrics.fontBoundingBoxAscent ??
-      widthMetrics.actualBoundingBoxAscent ??
+      widthMetrics.fontBoundingBoxAscent ||
+      widthMetrics.actualBoundingBoxAscent ||
       this.fontSize * 0.8;
     const descent =
-      widthMetrics.fontBoundingBoxDescent ??
-      widthMetrics.actualBoundingBoxDescent ??
+      widthMetrics.fontBoundingBoxDescent ||
+      widthMetrics.actualBoundingBoxDescent ||
       this.fontSize * 0.2;
 
     const height = Math.ceil(ascent + descent);