Wait for collaborator to leave before they rejoin.

Author: peterwilsoncc

tests/e2e/specs/collaboration/collaboration-sync.test.js

@@ -171,7 +171,7 @@ test.describe( 'Collaboration - Sync', () => {
 	} );
 
 	// Skipped: User C returning to editor triggers too many collaborators, causing failures.
-	test.skip( 'User C joins late and sees existing content from A and B', async ( {
+	test( 'User C joins late and sees existing content from A and B', async ( {
 		collaborationUtils,
 		editor,
 	} ) => {
@@ -185,6 +185,16 @@ test.describe( 'Collaboration - Sync', () => {
 		// present while A and B make edits.
 		await page3.goto( '/wp-admin/' );
 
+		// Wait for User C's awareness entry to expire on the server (30s timeout)
+		// by watching the button label drop from 3 to 2 collaborators.
+		const presenceButton = page2.getByRole( 'button', {
+			name: /Collaborators list/,
+		} );
+		await expect( presenceButton ).toHaveAccessibleName(
+			/2 online/,
+			{ timeout: 45000 }
+		);
+
 		// User A and B each add a block while User C is away.
 		await editor.insertBlock( {
 			name: 'core/paragraph',