fix(#1249): break sticky-bottom lock when user scrolls up during snap animation

docs/web-ui/shape.md

@@ -121,7 +121,15 @@ the smooth animation eases through positions that are technically
 `smoothScrollingUntil` timestamp gates the scroll handler — set to
 the animation end + ~80ms headroom, re-armed on each fresh snap.
 Programmatic `scrollTop` writes (the animation's per-frame update)
-fire scroll events that the gate swallows.
+fire scroll events that the gate swallows. One caveat: if live events
+arrive faster than the animation window (< 220ms apart), the
+MutationObserver keeps re-firing `snapToBottom()` which perpetually
+re-arms the gate — trapping the operator at the bottom with no way
+to scroll up or trigger `loadMore()`. Safety valve: even inside the
+guard the handler checks `isNearBottom()`; if the operator has
+scrolled away from the bottom, `stickToBottom` is immediately forced
+false. The MO's `if (stickToBottom)` check then stops re-arming
+snaps, and the gate expires within ≤220ms.
 
 **Post-append `MutationObserver`.** Renderers commonly call
 `api.row(cls, text)` to create the row shell then append more

frontend/packages/shared/src/terminal.js

@@ -158,12 +158,29 @@ export function create(opts) {
     pill.classList.add('visible');
   }
   log.addEventListener('scroll', () => {
-    // Swallow scroll events during smooth-snap animations — see
-    // docs/web-ui.md::Shared terminal pane (Mid-animation scroll-event
-    // guard).
-    if (Date.now() < smoothScrollingUntil) return;
-    stickToBottom = isNearBottom();
+    // Sticky-bottom intent tracking. Outside an animation this is
+    // straightforward — stickToBottom = isNearBottom(). During a
+    // smooth-snap animation we swallow most of the event to avoid a
+    // feedback loop (programmatic scrollTop changes → scroll events →
+    // new snap → cancels current rAF), but we MUST still let the user
+    // break out of sticky mode: if the user scrolls away from the
+    // bottom while a snap animation is in flight, honour that intent
+    // immediately so the MutationObserver stops re-firing snapToBottom()
+    // and the animation-guard window can expire naturally. Without this,
+    // live events arriving < 220ms apart permanently block scroll-to-top
+    // and loadMore() never fires. See docs/web-ui.md::Shared terminal
+    // pane (Mid-animation scroll-event guard).
+    const inAnim = Date.now() < smoothScrollingUntil;
+    const nearBottom = isNearBottom();
+    if (!inAnim) {
+      stickToBottom = nearBottom;
+    } else if (!nearBottom) {
+      // User scrolled up during an animation — break sticky mode so the
+      // MO stops calling snapToBottom() and the gate expires.
+      stickToBottom = false;
+    }
     if (stickToBottom) { unseen = 0; updatePill(); }
+    if (inAnim) return;
     // Auto-fetch older history when the user scrolls near the top — no
     // click required; the load-more pill stays as a visual indicator.
     if (rootLog.scrollTop <= LOAD_MORE_SCROLL_PX && histHasMore && !histLoading) {