fix(map): preserve empty facet selection

apps/catalog/src/mapPresentationProfile.ts

@@ -106,8 +106,9 @@ export function mapPresentationBindingIsAll(bindingId: string, filters: MapPrese
 
 /**
  * Apply one interactive facet-chip transition without collapsing the storage
- * contract. A missing field means unconstrained, while an explicitly persisted
- * empty array remains available to represent an intentional match-nothing view.
+ * contract. A missing field means that facet is not part of the current union,
+ * while one explicitly empty field represents the intentional match-nothing
+ * view after the final selected chip is switched off.
  */
 export function toggleMapPresentationFacetSelection(
   facets: Record<string, string[]>,
@@ -116,14 +117,30 @@ export function toggleMapPresentationFacetSelection(
 ) {
   const selected = facets[field];
   if (!selected?.includes(value)) {
-    return { ...facets, [field]: [...(selected ?? []), value] };
+    // A saved empty view can contain one or more empty facet arrays. They are
+    // a global zero-match sentinel, not active constraints, so selecting the
+    // first chip must replace them instead of leaving a hidden empty array that
+    // would continue to suppress every fact.
+    const activeFacets = Object.fromEntries(
+      Object.entries(facets).filter(([, values]) => values.length > 0),
+    );
+    return { ...activeFacets, [field]: [...(activeFacets[field] ?? []), value] };
   }
 
   const nextSelected = selected.filter((item) => item !== value);
   if (nextSelected.length > 0) return { ...facets, [field]: nextSelected };
 
-  const { [field]: _removed, ...unconstrained } = facets;
-  return unconstrained;
+  const { [field]: _removed, ...remaining } = facets;
+  const activeFacets = Object.fromEntries(
+    Object.entries(remaining).filter(([, values]) => values.length > 0),
+  );
+  if (Object.keys(activeFacets).length > 0) return activeFacets;
+
+  // Never collapse the last interactive deselection to `{}`: the renderer
+  // correctly interprets `{}` as unconstrained/all. Retain an explicit empty
+  // facet so the zero-selection state remains zero matches through any toggle
+  // cycle and through a later Application Save.
+  return { [field]: [] };
 }
 
 export function mapPresentationProfileForFact(
@@ -192,9 +209,8 @@ export function mapFactMatchesFilters(
     return [{ facet, selected }];
   });
 
-  // Persisted empty arrays are an explicit match-nothing state. Interactive
-  // deselection removes the field instead, so this branch is only reached for
-  // a deliberately saved empty view.
+  // Persisted empty arrays and the final interactive deselection are an
+  // explicit match-nothing state.
   if (selectedFacets.some(({ selected }) => selected.length === 0)) return false;
   if (selectedFacets.length === 0) return true;