Verify a Redis or Memcached object cache is actually working

A hosting provider's dashboard shows "Object Caching: Redis Enabled" for a site, and
the Redis Object Cache plugin is installed and activated. But database query counts in
Query Monitor still look the same as before Redis was supposedly turned on, and page
load times haven't improved.

SETUP: [Cloudways-hosted site, Redis add-on enabled through Cloudways' panel,
WP_REDIS_HOST and WP_REDIS_PORT both defined in wp-config.php, Redis Object Cache
plugin shows "Not enabled" in its own status widget on the Plugins page]

Diagnose this like someone who's seen a hosting dashboard lie about cache status
before, not by assuming Redis is working because a toggle says so:
1. Explain why "Not enabled" on the plugin's own status page overrides whatever the
   hosting dashboard claims, and what that specific message usually means: the
   object-cache.php drop-in file isn't present in wp-content, even though the plugin
   is active.
2. Walk through the actual verification steps: confirming object-cache.php exists in
   wp-content (not just the plugin folder), checking that WP_REDIS_HOST and
   WP_REDIS_PORT match what Cloudways actually provisioned rather than a placeholder
   value left from a config example, and testing a raw connection with a WP-CLI
   command like wp redis status or wp cache type.
3. Once the drop-in is confirmed working, explain how to verify it's actually reducing
   database load: comparing Query Monitor's query count and object cache hit ratio
   before and after a page reload, not just trusting that "enabled" means "helping."
4. Note the fix is almost entirely wp-admin plus file-manager or SFTP work here
   (activating the drop-in via the plugin's own "Enable Object Cache" button, or
   manually copying it if that button fails), it doesn't require a Cloudways support
   ticket unless the Redis service itself isn't actually provisioned on their end.
5. Flag the edge case: on a shared or multi-tenant Redis instance, cache keys need a
   unique prefix per site (via WP_CACHE_KEY_SALT), otherwise two sites on the same
   Redis instance can collide and one site's cached data can bleed into another's.