fix: column layouts would not stick — five separate faults

1. A language change rebuilt the column defs, which sets the anti-clobber
   guard, but the effect that clears it listened to only two of the rebuild's
   causes. Guard stuck on → every column change was silently discarded for the
   rest of the session. Now keyed on the rebuilt defs themselves, so any future
   cause is covered.
2. The cluster grid had no guard at all: the same rebuild wrote its defaults
   over the saved layout, in the cache AND the database. Unrecoverable.
3. Worked-before and cluster read their state before the active profile was
   known, so they looked up the unscoped cache key (always a miss) and then
   saved under the scoped one. They now wait for the scope and remount on a
   profile switch, like the main log.
4. GetUIPref returns an ERROR, not "", while the settings store is not yet
   scoped — deliberately distinct from "unset". The frontend read it as "no
   preference", rendered defaults, and the first column event overwrote the
   good copy. It now retries instead of giving up.
5. The QSL manager had no storageKey, so it shared the main log's layout and
   each rewrote the other.

Also: the DB write is debounced (a resize drag fired dozens of writes) with a
flush on close, and a rejected write is retried rather than dropped.

frontend/src/components/ClusterGrid.tsx

@@ -12,7 +12,7 @@ import {
 import { Button } from '@/components/ui/button';
 import { Checkbox } from '@/components/ui/checkbox';
 import { cleanSpotter, inferSpotMode, spotStatusKey } from '@/lib/spot';
-import { loadLocal, loadRemote, saveState, seedLocal } from '@/lib/gridPrefs';
+import { loadLocal, loadRemote, saveState, seedLocal, whenGridPrefsReady } from '@/lib/gridPrefs';
 import { useI18n } from '@/lib/i18n';
 
 type TFn = (key: string, vars?: Record<string, string | number>) => string;
@@ -371,10 +371,28 @@ export function ClusterGrid({ rows, spotStatus, onSpotClick }: Props) {
   // Localized column catalog — rebuilt when the language changes.
   const COL_CATALOG = useMemo(() => makeColCatalog(t), [t]);
 
-  const columnDefs = useMemo<ColDef<ClusterSpot>[]>(() => COL_CATALOG.map((c) => {
-    const { group: _g, label: _l, defaultVisible, ...rest } = c;
-    return { ...rest, hide: !defaultVisible };
-  }), [COL_CATALOG]);
+  // A rebuild makes AG Grid re-apply every colDef hide/width DEFAULT and fire the
+  // matching column events. Without this guard those events were persisted, so a
+  // single language change overwrote the saved cluster layout — in the cache AND
+  // in the database, with nothing to restore from.
+  const restoringRef = useRef(true);
+
+  const columnDefs = useMemo<ColDef<ClusterSpot>[]>(() => {
+    restoringRef.current = true;
+    return COL_CATALOG.map((c) => {
+      const { group: _g, label: _l, defaultVisible, ...rest } = c;
+      return { ...rest, hide: !defaultVisible };
+    });
+  }, [COL_CATALOG]);
+
+  // Re-apply the saved state after every rebuild, then re-enable saving.
+  useEffect(() => {
+    const api = gridRef.current?.api;
+    const local = loadLocal(COL_STATE_KEY);
+    if (api && local) api.applyColumnState({ state: local as ColumnState[], applyOrder: true });
+    const tm = window.setTimeout(() => { restoringRef.current = false; }, 0);
+    return () => window.clearTimeout(tm);
+  }, [columnDefs]);
 
   const defaultColDef = useMemo<ColDef>(() => ({
     sortable: true, resizable: true, filter: true, suppressMovable: false,
@@ -394,17 +412,20 @@ export function ClusterGrid({ rows, spotStatus, onSpotClick }: Props) {
     gridRef.current?.api?.refreshCells({ force: true });
   }, [spotStatus]);
 
-  function onGridReady(e: GridReadyEvent) {
+  // Restore AFTER the profile scope is known — this grid has no key= remount to
+  // save it from reading the wrong (unscoped) cache key at first paint.
+  async function onGridReady(e: GridReadyEvent) {
+    await whenGridPrefsReady();
     const local = loadLocal(COL_STATE_KEY);
     if (local) e.api.applyColumnState({ state: local as ColumnState[], applyOrder: true });
-    loadRemote(COL_STATE_KEY).then((remote) => {
-      if (remote && !local) {
-        e.api.applyColumnState({ state: remote as ColumnState[], applyOrder: true });
-        seedLocal(COL_STATE_KEY, remote);
-      }
-    });
+    const remote = await loadRemote(COL_STATE_KEY);
+    if (remote && !local) {
+      e.api.applyColumnState({ state: remote as ColumnState[], applyOrder: true });
+      seedLocal(COL_STATE_KEY, remote);
+    }
   }
   const saveColumnState = useCallback(() => {
+    if (restoringRef.current) return; // ignore the events fired by a column rebuild
     const state = gridRef.current?.api?.getColumnState();
     if (state) saveState(COL_STATE_KEY, state);
   }, []);