fix(chatui): respect reasoning panel scroll intent (#10243)

* fix(chatui): respect reasoning panel scroll intent

* Delete dashboard/tests/reasoningSidebarScroll.test.mjs

dashboard/src/components/chat/ReasoningSidebar.vue

@@ -6,7 +6,17 @@
         <v-btn icon="mdi-close" size="small" variant="text" @click="close" />
       </div>
 
-      <div ref="sidebarBody" class="reasoning-sidebar-body">
+      <div
+        ref="sidebarBody"
+        class="reasoning-sidebar-body"
+        tabindex="0"
+        @scroll="handleSidebarScroll"
+        @wheel.passive="handleSidebarInteraction"
+        @touchstart.passive="handleSidebarInteraction"
+        @touchmove.passive="handleSidebarInteraction"
+        @pointerdown="handleSidebarInteraction"
+        @keydown="handleSidebarInteraction"
+      >
         <ReasoningTimeline
           v-if="parts.length || reasoning"
           :parts="parts"
@@ -40,6 +50,10 @@ const props = defineProps<{
 }>();
 
 const sidebarBody = ref<HTMLElement | null>(null);
+const shouldStickToBottom = ref(true);
+let lastSidebarScrollTop = 0;
+let touchScrollY = 0;
+let scrollIntent = 0;
 
 const emit = defineEmits<{
   "update:modelValue": [value: boolean];
@@ -60,19 +74,90 @@ function close() {
 }
 
 function scrollToLatestActivity() {
-  if (!props.modelValue) return;
+  if (!props.modelValue || !shouldStickToBottom.value) return;
   void nextTick(() => {
     const body = sidebarBody.value;
-    if (!body) return;
+    if (!body || !shouldStickToBottom.value) return;
     body.scrollTop = body.scrollHeight;
+    lastSidebarScrollTop = Math.max(0, body.scrollTop);
   });
 }
 
+function handleSidebarInteraction(
+  event: WheelEvent | TouchEvent | PointerEvent | KeyboardEvent,
+) {
+  if (event instanceof WheelEvent) {
+    if (event.ctrlKey || event.deltaY === 0) return;
+    scrollIntent = Math.sign(event.deltaY);
+  } else if (event.type === "touchstart" || event.type === "touchmove") {
+    const touch = (event as TouchEvent).touches[0];
+    if (!touch) return;
+    if (event.type === "touchstart") {
+      touchScrollY = touch.clientY;
+      return;
+    }
+    scrollIntent = Math.sign(touchScrollY - touch.clientY);
+    touchScrollY = touch.clientY;
+  } else if (event instanceof KeyboardEvent) {
+    const target = event.target as HTMLElement;
+    if (
+      target.closest("input, textarea, select, [contenteditable], button, a")
+    ) {
+      return;
+    }
+    if (
+      ["ArrowUp", "PageUp", "Home"].includes(event.key) ||
+      (event.key === " " && event.shiftKey)
+    ) {
+      scrollIntent = -1;
+    } else if (["ArrowDown", "PageDown", "End", " "].includes(event.key)) {
+      scrollIntent = 1;
+    } else {
+      return;
+    }
+  } else {
+    if (event.target !== sidebarBody.value) return;
+    scrollIntent = 0;
+    shouldStickToBottom.value = false;
+  }
+  if (scrollIntent < 0) shouldStickToBottom.value = false;
+}
+
+function handleSidebarScroll() {
+  const body = sidebarBody.value;
+  if (!body) return;
+  const maxScrollTop = Math.max(0, body.scrollHeight - body.clientHeight);
+  const scrollTop = Math.max(0, body.scrollTop);
+  const previousTop = Math.min(lastSidebarScrollTop, maxScrollTop);
+  const isAwayFromBottom = maxScrollTop - scrollTop > 2;
+  if (scrollTop < previousTop) {
+    shouldStickToBottom.value = false;
+  } else if (
+    scrollTop > previousTop &&
+    !isAwayFromBottom &&
+    scrollIntent >= 0
+  ) {
+    shouldStickToBottom.value = true;
+  }
+  lastSidebarScrollTop = scrollTop;
+}
+
 watch(
-  () => [props.modelValue, props.reasoning, props.parts],
-  scrollToLatestActivity,
-  { deep: true, flush: "post", immediate: true },
+  () => props.modelValue,
+  (open) => {
+    if (!open) return;
+    shouldStickToBottom.value = true;
+    scrollIntent = 0;
+    lastSidebarScrollTop = 0;
+    scrollToLatestActivity();
+  },
+  { flush: "post", immediate: true },
 );
+
+watch(() => [props.reasoning, props.parts], scrollToLatestActivity, {
+  deep: true,
+  flush: "post",
+});
 </script>
 
 <style scoped>