fix(app): prevent scrollend position rollback

Discard virtualizer measurement corrections suppressed during an active user gesture instead of replaying stale offsets at scrollend. Preserve post-scroll live anchoring and add unit plus Electron coverage for ordinary scrolling without updates.

app/src/renderer/src/session-timeline-scroll-policy.mjs

@@ -1,13 +1,8 @@
 export function createSessionTimelineScrollPolicy({ isUserScrolling, writeScroll }) {
   let explicitDepth = 0;
-  let deferredAdjustment = 0;
-  let deferredInstance = null;
 
   function scrollToFn(offset, options = {}, instance) {
     if (explicitDepth === 0 && isUserScrolling()) {
-      const adjustment = Number(options.adjustments);
-      if (Number.isFinite(adjustment)) deferredAdjustment += adjustment;
-      deferredInstance = instance;
       return;
     }
     writeScroll(offset, options, instance);
@@ -22,19 +17,8 @@ export function createSessionTimelineScrollPolicy({ isUserScrolling, writeScroll
     }
   }
 
-  function flushDeferredAdjustment(instance = deferredInstance) {
-    if (isUserScrolling() || deferredAdjustment === 0 || !instance?.scrollElement) return false;
-    const adjustment = deferredAdjustment;
-    deferredAdjustment = 0;
-    deferredInstance = null;
-    const offset = Number(instance.scrollElement.scrollTop) || 0;
-    writeScroll(offset, { behavior: 'auto', adjustments: adjustment }, instance);
-    return true;
-  }
-
   return {
     scrollToFn,
     runExplicit,
-    flushDeferredAdjustment,
   };
 }

app/src/renderer/src/session-timeline-viewport.mjs

@@ -133,10 +133,6 @@ export function useSessionTimelineViewport({
     tailFollowReady.value = true;
   }
 
-  function settleUserScroll() {
-    return scrollPolicy.flushDeferredAdjustment(virtualizer.value);
-  }
-
   return {
     virtualRows,
     totalSize,
@@ -145,7 +141,6 @@ export function useSessionTimelineViewport({
     scrollToIndex,
     scrollToEnd,
     isFollowingTail,
-    settleUserScroll,
     resetForInitialSnapshot,
     completeInitialSnapshot,
   };

app/src/renderer/src/views/SessionDetail.vue

@@ -63,7 +63,6 @@ const liveReloadCoordinator = createSessionLiveReloadCoordinator({
 });
 
 function handleUserScrollEnd() {
-  timelineViewport.settleUserScroll();
   if (active.value) void liveReloadCoordinator.flush();
 }