Why can one AI assistant appear in Discord, Feishu, and on your phone at the same time?

Answer: The apps are doorways into one assistant running in one place, which holds the memory and the tasks

Each app has its own separate copy of the assistant, and the copies just happen to answer alike — Separate copies would each start from a blank slate: a reminder set in Discord would be unknown in Feishu, and a task half done on the phone would not continue elsewhere. Many simple bots are deployed exactly that way, one install per platform, and then they are not one assistant but several that merely share a name.

The apps are doorways into one assistant running in one place, which holds the memory and the tasks ✓ — Correct! The assistant itself runs as a single service in one place, with its memory, tools and scheduled tasks. Discord, Feishu and the phone app are just different front doors: each one passes your messages to that service and shows you its replies. Because there is one assistant behind all the doors, it remembers what you said in one app when you continue in another, and it can keep working on a task even when none of the apps is open.

Your phone forwards every message to the other apps, so they all stay in step — The phone is just another client, no more central than Discord or Feishu. Switch it off and the assistant still answers in the other apps, because the work and the memory live in the shared service, not on any one device.