Tests: Add collaboration server tests and remove legacy sync tests

Adds 67 PHPUnit tests for WP_HTTP_Polling_Collaboration_Server covering
document sync, awareness, undo/redo, compaction, permissions, cursor
mechanics, race conditions, cron cleanup, and the backward-compatible
wp-sync/v1 route. Adds E2E tests for 3-user presence, sync, and
undo/redo. Removes the old sync server tests. Updates REST schema
setup and fixtures for the new collaboration endpoints.

Author: josephfusco

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

@@ -0,0 +1,109 @@
+/**
+ * Tests for collaborative editing presence (awareness).
+ *
+ * Verifies that collaborator avatars, names, and leave events
+ * propagate correctly between three concurrent users.
+ *
+ * @package WordPress
+ * @since 7.0.0
+ */
+
+/**
+ * Internal dependencies
+ */
+import { test, expect, SYNC_TIMEOUT } from './fixtures';
+
+test.describe( 'Collaboration - Presence', () => {
+	test( 'All 3 collaborator avatars are visible', async ( {
+		collaborationUtils,
+		page,
+	} ) => {
+		await collaborationUtils.createCollaborativePost( {
+			title: 'Presence Test - 3 Users',
+		} );
+
+		const { page2, page3 } = collaborationUtils;
+
+		// Each user sees the collaborators list button (indicates others are present).
+		await expect(
+			page.getByRole( 'button', { name: /Collaborators list/ } )
+		).toBeVisible( { timeout: SYNC_TIMEOUT } );
+
+		await expect(
+			page2.getByRole( 'button', { name: /Collaborators list/ } )
+		).toBeVisible( { timeout: SYNC_TIMEOUT } );
+
+		await expect(
+			page3.getByRole( 'button', { name: /Collaborators list/ } )
+		).toBeVisible( { timeout: SYNC_TIMEOUT } );
+	} );
+
+	test( 'Collaborator names appear in popover', async ( {
+		collaborationUtils,
+		page,
+	} ) => {
+		await collaborationUtils.createCollaborativePost( {
+			title: 'Presence Test - Names',
+		} );
+
+		// User A opens the collaborators popover.
+		const presenceButton = page.getByRole( 'button', {
+			name: /Collaborators list/,
+		} );
+		await expect( presenceButton ).toBeVisible( {
+			timeout: SYNC_TIMEOUT,
+		} );
+		await presenceButton.click();
+
+		// The popover should list both collaborators by name.
+		// Use the presence list item class to avoid matching snackbar toasts.
+		await expect(
+			page.locator( '.editor-collaborators-presence__list-item-name', { hasText: 'Test Collaborator' } )
+		).toBeVisible();
+
+		await expect(
+			page.locator( '.editor-collaborators-presence__list-item-name', { hasText: 'Another Collaborator' } )
+		).toBeVisible();
+	} );
+
+	test( 'User C leaves, A and B see updated presence', async ( {
+		collaborationUtils,
+		page,
+	} ) => {
+		await collaborationUtils.createCollaborativePost( {
+			title: 'Presence Test - Leave',
+		} );
+
+		// Verify all 3 users see the collaborators button initially.
+		await expect(
+			page.getByRole( 'button', { name: /Collaborators list/ } )
+		).toBeVisible( { timeout: SYNC_TIMEOUT } );
+
+		// Navigate User C away from the editor to stop their polling.
+		// Avoids closing the context directly which corrupts Playwright state.
+		await collaborationUtils.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 = page.getByRole( 'button', {
+			name: /Collaborators list/,
+		} );
+		await expect( presenceButton ).toHaveAccessibleName(
+			/2 online/,
+			{ timeout: 45000 }
+		);
+
+		// Open the popover once, then verify the list contents.
+		await presenceButton.click();
+
+		// "Another Collaborator" (User C) should no longer appear in the presence list.
+		await expect(
+			page.locator( '.editor-collaborators-presence__list-item-name', { hasText: 'Another Collaborator' } )
+		).not.toBeVisible();
+
+		// "Test Collaborator" (User B) should still be listed.
+		await expect(
+			page.locator( '.editor-collaborators-presence__list-item-name', { hasText: 'Test Collaborator' } )
+		).toBeVisible();
+	} );
+} );