Fix help response thread overwrites — fetch current note from DB before appending

Replies now read the existing response_note from Supabase before appending
the new reply, avoiding race conditions where the local reactive state
could be stale. The append logic moved from the UI to the store's respond()
function with an appendToExisting flag.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: amyleesterling

src/components/CellLibraryPanel.vue

@@ -436,16 +436,11 @@ function getAnnotationLayers(): string[] {
 
 async function submitResponse(req: HelpRequest, andResolve = false) {
   if (!responseNote.value.trim()) return;
-  // If there's an existing response, append as a thread entry
-  const userName = backend.userName || 'Unknown';
-  let note = responseNote.value.trim();
-  if (req.responseNote) {
-    note = `${req.responseNote}\n---\n${userName}: ${note}`;
-  }
   const payload = {
-    note,
+    note: responseNote.value.trim(),
     url: responseUrl.value.trim() || undefined,
     annotationLayer: responseAnnotationLayer.value.trim() || undefined,
+    appendToExisting: !!req.responseNote,  // signal to append, not replace
   };
   if (andResolve) {
     await helpStore.resolve(req.id, payload);

src/store.ts

@@ -1061,13 +1061,28 @@ export const useHelpRequestStore = defineStore('helpRequests', () => {
   }
 
   /** Add a response to a help request WITHOUT resolving it. */
-  async function respond(id: string, response: { note?: string; url?: string; annotationLayer?: string }) {
+  async function respond(id: string, response: { note?: string; url?: string; annotationLayer?: string; appendToExisting?: boolean }) {
     const backend = useProofreadingBackendStore();
     const responderName = backend.userName || backend.userEmail?.split('@')[0] || 'Anonymous';
+
+    // If appending to an existing thread, fetch current note from DB to avoid overwrites
+    let finalNote = response.note || '';
+    if (response.appendToExisting && response.note) {
+      const { data } = await supabase
+        .from('help_requests')
+        .select('response_note')
+        .eq('id', id)
+        .single();
+      const existing = data?.response_note || '';
+      if (existing) {
+        finalNote = `${existing}\n---\n${responderName}: ${response.note}`;
+      }
+    }
+
     const updateData: Record<string, any> = {
       resolved_by_name: responderName,
     };
-    if (response.note) updateData.response_note = response.note;
+    if (finalNote) updateData.response_note = finalNote;
     if (response.url) updateData.response_url = response.url;
     if (response.annotationLayer) updateData.response_annotation_layer = response.annotationLayer;
 
@@ -1083,7 +1098,7 @@ export const useHelpRequestStore = defineStore('helpRequests', () => {
     const r = requests.value.find(x => x.id === id);
     if (r) {
       r.resolvedByName = responderName;
-      if (response.note) r.responseNote = response.note;
+      if (finalNote) r.responseNote = finalNote;
       if (response.url) r.responseUrl = response.url;
       if (response.annotationLayer) r.responseAnnotationLayer = response.annotationLayer;
     }