Fix: Channels header disappears in Find Channels dialog during search (#35202)

The "Channels" header was flashing and then disappearing when typing in
the Find Channels dialog (Ctrl/Cmd+K). This was caused by the
fetchUsersAndChannels method returning results without the groups
structure that was introduced in MM-62990.

webapp/channels/src/components/suggestion/switch_channel_provider.test.tsx

@@ -587,7 +587,12 @@ describe('components/SwitchChannelProvider', () => {
         ];
 
         expect(resultsCallback).toHaveBeenCalledWith(expect.objectContaining({
-            terms: expectedOrder,
+            groups: expect.arrayContaining([
+                expect.objectContaining({
+                    key: 'channels',
+                    terms: expectedOrder,
+                }),
+            ]),
         }));
     });
 
@@ -670,7 +675,12 @@ describe('components/SwitchChannelProvider', () => {
         ];
 
         expect(resultsCallback).toHaveBeenCalledWith(expect.objectContaining({
-            terms: expectedOrder,
+            groups: expect.arrayContaining([
+                expect.objectContaining({
+                    key: 'channels',
+                    terms: expectedOrder,
+                }),
+            ]),
         }));
     });
 
@@ -757,7 +767,12 @@ describe('components/SwitchChannelProvider', () => {
             'channel_other_user1',
         ];
         expect(resultsCallback).toHaveBeenCalledWith(expect.objectContaining({
-            terms: expectedOrder,
+            groups: expect.arrayContaining([
+                expect.objectContaining({
+                    key: 'channels',
+                    terms: expectedOrder,
+                }),
+            ]),
         }));
     });
 
@@ -906,7 +921,12 @@ describe('components/SwitchChannelProvider', () => {
         ];
 
         expect(resultsCallback).toHaveBeenCalledWith(expect.objectContaining({
-            terms: channelsFromActiveTeams,
+            groups: expect.arrayContaining([
+                expect.objectContaining({
+                    key: 'channels',
+                    terms: channelsFromActiveTeams,
+                }),
+            ]),
         }));
     });
 
@@ -992,7 +1012,12 @@ describe('components/SwitchChannelProvider', () => {
         ];
 
         expect(resultsCallback).toHaveBeenCalledWith(expect.objectContaining({
-            terms: expectedOrder,
+            groups: expect.arrayContaining([
+                expect.objectContaining({
+                    key: 'channels',
+                    terms: expectedOrder,
+                }),
+            ]),
         }));
     });
 

webapp/channels/src/components/suggestion/switch_channel_provider.tsx

@@ -655,9 +655,13 @@ export default class SwitchChannelProvider extends Provider {
 
         resultsCallback({
             matchedPretext: channelPrefix,
-            items: combinedItems,
-            terms: combinedTerms,
-            component: ConnectedSwitchChannelSuggestion,
+            groups: [{
+                key: 'channels',
+                label: defineMessage({id: 'suggestion.channels', defaultMessage: 'Channels'}),
+                items: combinedItems,
+                terms: combinedTerms,
+                component: ConnectedSwitchChannelSuggestion,
+            }],
         });
     }