Fix renderMdToFragment infinite loop on unmatched ** / backtick (streaming-partial freeze)

index.html

@@ -1218,11 +1218,18 @@ function el(tag, opts){
   return e;
 }
 
-/* Safe markdown — escape implicit, only **bold** and `code` are recognized. */
+/* Safe markdown — escape implicit, only **bold** and `code` are recognized.
+   IMPORTANT: streaming partial yields can land mid-`**` or mid-`` ` `` pair
+   (e.g. cumulative text "... **The" before the closing `**` arrives). The
+   unmatched-opener cases below are critical: without them the plain-run
+   inner loop breaks immediately on the same `**`, the slice is empty, `i`
+   doesn't advance, and the outer while loops forever — freezing the tab
+   with "Page Unresponsive" once a streaming chunk happens to end mid-pair. */
 function renderMdToFragment(s){
   const frag = document.createDocumentFragment();
   let i = 0;
   while (i < s.length){
+    const startI = i;  // safety: guarantee forward progress every iteration
     // **bold**
     if (s[i] === '*' && s[i+1] === '*'){
       const end = s.indexOf('**', i + 2);
@@ -1231,6 +1238,10 @@ function renderMdToFragment(s){
         i = end + 2;
         continue;
       }
+      // Unmatched opening (mid-stream partial) — render as plain text and advance.
+      frag.appendChild(document.createTextNode('**'));
+      i += 2;
+      continue;
     }
     // `code`
     if (s[i] === '`'){
@@ -1240,6 +1251,10 @@ function renderMdToFragment(s){
         i = end + 1;
         continue;
       }
+      // Unmatched opening — render as plain text and advance.
+      frag.appendChild(document.createTextNode('`'));
+      i += 1;
+      continue;
     }
     // Plain run — find next special char
     let next = i;
@@ -1250,6 +1265,8 @@ function renderMdToFragment(s){
     }
     frag.appendChild(document.createTextNode(s.slice(i, next)));
     i = next;
+    // Defense in depth: never let the outer loop spin without progress.
+    if (i === startI) i++;
   }
   return frag;
 }