fix(reasoning): re-scroll PDF when re-clicking the active iteration

The watch-based plumbing from iteration click to PDF scroll relied on a
"flip via null" pattern (assign null then the value) to coerce Vue into
re-firing the watcher. Vue 3 collapses synchronous mutations of the same
ref and only delivers the final value, so the trick was a no-op: a second
click on the same iteration left the document view stuck on the previous
page. The bug only showed when the trace had a single iteration — with
several, the user naturally clicks different ones and the value really
changes.

Replace the watch chain with imperative dispatch. ReasoningPanel now just
emits iterationFocus; ReasoningWorkspace handles it by calling the graph
focus and the new StructureViewer.scrollToFocused method directly. Both
side effects fire on every click regardless of state.

frontend/src/features/analysis/ui/StructureViewer.vue

@@ -284,29 +284,33 @@ watch(
 // When the caller sets a focused self_ref (e.g. the user clicked a node in
 // the graph), find which page that element lives on and jump to it. The
 // overlay redraw will then show the dashed focus ring around its bbox.
-watch(
-  () => props.focusedSelfRef,
-  (ref) => {
-    if (!ref) {
-      nextTick(drawOverlay)
+function scrollToFocused(ref: string | null): void {
+  if (!ref) {
+    nextTick(drawOverlay)
+    return
+  }
+  for (const page of props.pages) {
+    if (page.elements.some((e) => e.self_ref === ref)) {
+      if (selectedPage.value !== page.page_number) {
+        selectedPage.value = page.page_number
+        // Let <img> reload before drawing — drawOverlay runs on @load.
+      } else {
+        nextTick(drawOverlay)
+      }
       return
     }
-    for (const page of props.pages) {
-      if (page.elements.some((e) => e.self_ref === ref)) {
-        if (selectedPage.value !== page.page_number) {
-          selectedPage.value = page.page_number
-          // Let <img> reload before drawing — drawOverlay runs on @load.
-        } else {
-          nextTick(drawOverlay)
-        }
-        return
-      }
-    }
-    // Ref not on any page (e.g. a #/body node) — just redraw to clear the
-    // previous focus ring.
-    nextTick(drawOverlay)
-  },
-)
+  }
+  // Ref not on any page (e.g. a #/body node) — just redraw to clear the
+  // previous focus ring.
+  nextTick(drawOverlay)
+}
+
+watch(() => props.focusedSelfRef, scrollToFocused)
+
+// Imperative entry point so callers can re-trigger a scroll on the same
+// self_ref (the watch above only fires on value change). Used by the
+// reasoning workspace when the user re-clicks the active iteration card.
+defineExpose({ scrollToFocused })
 </script>
 
 <style scoped>

frontend/src/features/reasoning/store.ts

@@ -96,11 +96,10 @@ export const useReasoningStore = defineStore('reasoning', () => {
   }
 
   function setActiveIteration(n: number | null): void {
-    // Flip via null first so a click on the *same* iteration still fires
-    // downstream watchers (PDF scroll, graph pan). Otherwise Vue sees
-    // "no change" and the second click is a silent no-op — painful UX when
-    // only one iteration exists.
-    activeIteration.value = null
+    // Pure state — drives the active-card highlight in the iteration list.
+    // Side effects (graph pan, PDF scroll) are dispatched imperatively from
+    // ReasoningWorkspace.onIterationFocus so re-clicking the same iteration
+    // still re-focuses both views (a watch here would no-op on same value).
     activeIteration.value = n
   }
 

frontend/src/features/reasoning/ui/DocumentView.vue

@@ -5,6 +5,7 @@
     </div>
     <StructureViewer
       v-else
+      ref="structureViewerRef"
       :pages="pages"
       :document-id="docId"
       :visited-by-self-ref="visitedBySelfRef"
@@ -28,7 +29,7 @@
  *   - clicking a bbox emits `elementFocus` so the graph can mirror the
  *     selection (bidirectional sync handled in ReasoningWorkspace).
  */
-import { computed } from 'vue'
+import { computed, ref } from 'vue'
 
 import StructureViewer from '../../analysis/ui/StructureViewer.vue'
 import { useAnalysisStore } from '../../analysis/store'
@@ -42,6 +43,17 @@ const props = defineProps<{
 }>()
 const emit = defineEmits<{ elementFocus: [selfRef: string] }>()
 
+const structureViewerRef = ref<InstanceType<typeof StructureViewer> | null>(null)
+
+// Imperative passthrough so the reasoning workspace can re-trigger a scroll
+// on the same self_ref (e.g. user re-clicks the active iteration card —
+// the prop hasn't changed so the watch wouldn't fire).
+function scrollToFocused(selfRef: string | null): void {
+  structureViewerRef.value?.scrollToFocused(selfRef)
+}
+
+defineExpose({ scrollToFocused })
+
 const analysisStore = useAnalysisStore()
 const reasoningStore = useReasoningStore()
 const { t } = useI18n()

frontend/src/features/reasoning/ui/ReasoningPanel.vue

@@ -79,7 +79,7 @@
           :key="it.iteration"
           :iteration="it"
           :active="store.activeIteration === it.iteration"
-          @focus="onFocus"
+          @focus="(n) => emit('iterationFocus', n)"
         />
       </div>
     </section>
@@ -99,8 +99,6 @@ import {
   applyReasoningOverlay,
   buildDegradedOverlay,
   clearReasoningOverlay,
-  focusIteration,
-  nodeIdForSectionRef,
 } from '../graphReasoningOverlay'
 import { useReasoningStore } from '../store'
 import IterationCard from './IterationCard.vue'
@@ -115,6 +113,11 @@ const props = defineProps<{
   cy: Core | null
 }>()
 
+// Iteration clicks bubble up to the workspace, which dispatches focus to
+// both the graph and the PDF directly — keeping the panel ignorant of its
+// siblings and avoiding watch-based plumbing that misfires on repeat clicks.
+const emit = defineEmits<{ iterationFocus: [iteration: number] }>()
+
 const store = useReasoningStore()
 const { t } = useI18n()
 
@@ -186,14 +189,6 @@ watch(
   { immediate: true },
 )
 
-function onFocus(iteration: number): void {
-  store.setActiveIteration(iteration)
-  if (!props.cy) return
-  const hit = store.iterations.find((i) => i.iteration === iteration)
-  if (!hit || !hit.present) return
-  focusIteration(props.cy, nodeIdForSectionRef(hit.sectionRef))
-}
-
 function onClear(): void {
   if (props.cy) clearReasoningOverlay(props.cy)
   store.reset()

frontend/src/features/reasoning/ui/ReasoningWorkspace.vue

@@ -69,11 +69,12 @@
            and the initial scroll never fires. -->
       <DocumentView
         v-show="mode === 'document'"
+        ref="documentViewRef"
         :doc-id="docId"
         :focused-self-ref="focusedSelfRef"
         @element-focus="onPdfElementFocus"
       />
-      <ReasoningPanel :cy="graphCy" />
+      <ReasoningPanel :cy="graphCy" @iteration-focus="onIterationFocus" />
     </div>
 
     <RunReasoningDialog :doc-id="docId" :doc-filename="docFilename" />
@@ -86,6 +87,7 @@ import { computed, onBeforeUnmount, ref, watch } from 'vue'
 import GraphView from '../../analysis/ui/GraphView.vue'
 import { useI18n } from '../../../shared/i18n'
 import { fetchReasoningGraph } from '../api'
+import { focusIteration, nodeIdForSectionRef } from '../graphReasoningOverlay'
 import { useReasoningStore } from '../store'
 import DocumentView from './DocumentView.vue'
 import ReasoningPanel from './ReasoningPanel.vue'
@@ -105,6 +107,7 @@ const reasoningStore = useReasoningStore()
 
 const graphViewRef = ref<InstanceType<typeof GraphView> | null>(null)
 const graphCy = computed(() => graphViewRef.value?.cy ?? null)
+const documentViewRef = ref<InstanceType<typeof DocumentView> | null>(null)
 
 const mode = ref<WorkspaceMode>('graph')
 
@@ -126,24 +129,21 @@ function onPdfElementFocus(selfRef: string): void {
   graphViewRef.value?.selectBySelfRef(selfRef)
 }
 
-// Click on an iteration card in the reasoning panel flows through
-// `reasoningStore.setActiveIteration(n)`. That path already focuses the
-// cytoscape node (in ReasoningPanel.onFocus); we mirror it into the PDF
-// viewer by resolving the active iteration's section_ref and piping it
-// into our shared focus. Done at the workspace level — not inside the
-// panel — because the panel doesn't know it has a PDF sibling.
-watch(
-  () => reasoningStore.activeIteration,
-  (n) => {
-    if (n === null) return
-    const hit = reasoningStore.iterations.find((i) => i.iteration === n)
-    if (!hit?.present || !hit.sectionRef) return
-    // Flip via null so StructureViewer's watch on `focusedSelfRef` re-fires
-    // even when clicking the same iteration twice (same sectionRef).
-    focusedSelfRef.value = null
-    focusedSelfRef.value = hit.sectionRef
-  },
-)
+// Click on an iteration card in the reasoning panel. We dispatch focus to
+// both the graph and the PDF imperatively (rather than via watches on
+// `activeIteration` / `focusedSelfRef`). Watches misfire when the user
+// re-clicks the same iteration: Vue collapses synchronous "flip via null"
+// mutations and only sees the final value, equal to the previous one — so
+// nothing scrolls. Calling `focusIteration` and `scrollToFocused` directly
+// works on every click regardless of state.
+function onIterationFocus(iteration: number): void {
+  reasoningStore.setActiveIteration(iteration)
+  const hit = reasoningStore.iterations.find((i) => i.iteration === iteration)
+  if (!hit?.present || !hit.sectionRef) return
+  if (graphCy.value) focusIteration(graphCy.value, nodeIdForSectionRef(hit.sectionRef))
+  focusedSelfRef.value = hit.sectionRef
+  documentViewRef.value?.scrollToFocused(hit.sectionRef)
+}
 
 // Reset the reasoning store when switching docs — a trace imported for one
 // document is meaningless on another. The main-pane mode resets too so a