Tail-follow scroll in source

src/lib/TraceViewer.svelte

@@ -93,17 +93,20 @@
       msg._visible = true;
       focusedIdx = mi;
       await tick();
-      scrollToFocused('smooth');
+      followTail();
       await wait(40);
 
       for (let bi = 0; bi < msg.blocks.length; bi++) {
         if (skipFlag) break;
         msg._visibleBlocks = bi + 1;
+        await tick();
+        followTail();
         const block = msg.blocks[bi];
         if (block.kind === 'text' || block.kind === 'thinking') {
           await typeBlock(block);
         } else {
           await wait(90);
+          followTail();
         }
       }
       if (skipFlag) break;
@@ -128,9 +131,22 @@
       if (skipFlag) break;
       block._typedText = full.slice(0, c);
       await wait(tickMs);
+      followTail();
     }
     block._typedText = full;
     block._typing = false;
+    followTail();
+  }
+
+  // Terminal-style tail: while content is streaming, keep the bottom of the
+  // scroll container pinned — but only if the user hasn't scrolled away.
+  function followTail() {
+    if (!listEl) return;
+    const distanceFromBottom =
+      listEl.scrollHeight - listEl.scrollTop - listEl.clientHeight;
+    if (distanceFromBottom < 240) {
+      listEl.scrollTop = listEl.scrollHeight;
+    }
   }
 
   function revealAll() {