If you use Minecraft Code Connection (https://minecraft.gamepedia.com/Code_Connection, https://minecraft.makecode.com/) in Bedrock Edition (which requires cheats on / operator command permission), then an agent entity spawns as expected. The agent is unmovable (besides by code connection scripts) and invincible. The agent is present in the world whenever its creator is connected.

The problem is that while its creator is connected, the agent can't be removed. Even if the creator closes code connection and reconnects, the agent comes back. Even if operator commands are disabled for the creator, the agent still exists, except now the creator can't control it at all.

Even if the creator teleports their agent somewhere far out of the way, the agent back teleports to the player whenever they enter or leave the nether, regardless of whether the code connection is active and whether the player still has operator command permission.

For me, this is really annoying because whenever I play on a friend group's world on my xbox (where I'm not using code connection; it's been a long time since I've even used the code connection!), the agent is usually present at the nether portal near the spawn portal and I'm constantly explaining what it is to people and apologizing for leaving it at their base where they can't do anything about it. Moving it means I need to go find a far away nether portal or go to my windows pc and set up code connection again.

It looks like this same issue existed for the Education Edition, and was separately fixed for it, but the fix never made it into Bedrock Edition: https://minecrafteducation.zendesk.com/hc/en-us/community/posts/360028792492-Remove-Agent-from-world