TUL/fix: address review - only default operator when value has none

Previously getCurrentFilters set operator='equals' on every non-range filter,
even when the URL value already embedded an operator (e.g. "foo,contains"),
which could confuse consumers reading filter.operator directly (e.g. CSV export).
Now default to 'equals' only when no value carries an operator suffix (contains a
comma), matching SearchOptions.toRestUrl. Added a spec fixture for an
operator-embedded value asserting the operator stays unset. Per Copilot review on #1368.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: milanmajchrak

src/app/core/shared/search/search-configuration.service.spec.ts

@@ -20,7 +20,8 @@ describe('SearchConfigurationService', () => {
   const prefixFilter = {
     'f.author': ['another value'],
     'f.date.min': ['2013'],
-    'f.date.max': ['2018']
+    'f.date.max': ['2018'],
+    'f.subject': ['some subject,contains']
   };
   const defaults = new PaginatedSearchOptions({
     pagination: Object.assign(new PaginationComponentOptions(), { id: 'page-id', currentPage: 1, pageSize: 20 }),
@@ -32,7 +33,9 @@ describe('SearchConfigurationService', () => {
 
   const backendFilters = [
     new SearchFilter('f.author', ['another value'], 'equals'),
-    new SearchFilter('f.date', ['[2013 TO 2018]'], 'equals')
+    new SearchFilter('f.date', ['[2013 TO 2018]'], 'equals'),
+    // value already carries an operator suffix -> operator must stay unset (not overridden to equals)
+    new SearchFilter('f.subject', ['some subject,contains'])
   ];
 
   const routeService = jasmine.createSpyObj('RouteService', {

src/app/core/shared/search/search-configuration.service.ts

@@ -196,11 +196,15 @@ export class SearchConfigurationService implements OnDestroy {
               filters.push(new SearchFilter(realKey, ['[' + min + ' TO ' + max + ']'], 'equals'));
             }
           } else {
-            // Default to the "equals" operator when a filter value carries none (e.g. a legacy or
-            // crawled URL like "f.subject=foo" instead of "f.subject=foo,equals"). Without this the
-            // backend rejects the operator-less filter with HTTP 422. Values that already embed an
-            // operator (contain a comma) keep it - see SearchOptions.toRestUrl. dspace-customers#781.
-            filters.push(new SearchFilter(key, filterParams[key], 'equals'));
+            // Default to the "equals" operator only when a filter value carries none (e.g. a legacy
+            // or crawled URL like "f.subject=foo" instead of "f.subject=foo,equals"), which the
+            // backend would otherwise reject with HTTP 422. Values that already embed an operator
+            // (contain a comma, e.g. "foo,contains") keep it and leave SearchFilter.operator unset,
+            // matching SearchOptions.toRestUrl and consumers that read filter.operator directly
+            // (e.g. CSV export). dspace-customers#781.
+            const values = filterParams[key];
+            const operator = values.every((value) => value.includes(',')) ? undefined : 'equals';
+            filters.push(new SearchFilter(key, values, operator));
           }
         });
         return filters;