Track nearby agents list to avoid alerts caused by teleporting in/out of a region

[niciphilly]

Environment

Alchemy Test 26.2.0.62420 (64bit)
Release Notes

CPU: Intel(R) Core(TM) Ultra 9 185H (4800 MHz)
Memory: 31445 MB
Concurrency: 22
OS Version: Linux 7.0.10-arch1-1 #1 SMP PREEMPT_DYNAMIC Sat, 23 May 2026 14:21:20 +0000 x86_64
Graphics Card Vendor: Intel
Graphics Card: Mesa Intel(R) Arc(tm) Graphics (MTL)

OpenGL Version: 4.6 (Compatibility Profile) Mesa 26.1.1-arch1.2

Window size: 2880x1602
Font Size Adjustment: 96pt
UI Scaling: 1
Draw distance: 128m
Bandwidth: 3000kbit/s
LOD factor: 1.25
Render quality: 2
Texture memory: 0MB
Disk cache: Max size 11468 MB (37.5% used)
HiDPI display mode: true

RestrainedLove API: (disabled)
J2C Decoder Version: OpenJPEG runtime: 2.5.4
Audio Driver Version: FAudio 3.249.148 — Default Device (2ch @ 44100Hz)
Dullahan: 1.23.0.202605311253
CEF: 148.0.9+g0d9d52a+chromium-148.0.7778.180
Chromium: 148.0.7778.180
LibVLC Version: 3.0.23
Voice Server Version: Not Connected
Compiler Version: GCC 160101
June 03 2026 09:28:35

Description

When you enable Radar Alerts and teleport to a new sim you get notifications that the avatars from the previous sim have left the sim you have just arrived. That's obviously wrong. Probably the expected behavior in that situation would be not no send a notification at all since you were the one leaving the sim.
The option "Log Alerts to Chat" makes no different, it only causes the wrong sim names being logged to chat.

I am seeing this for a very on the development version of Alchemy. But I am not sure when it started.

Reproduction steps

1. Activate Radar Alerts
2. Go to a sim with people
3. Teleport somewhere else
4. Get a message that the people have left the sim on which you have just arrived

[DarlCat]

Thanks for this, validated as current in 26.2.

This is a years-old behavior with Alchemy, and an enhancement is the best way for us to triage this request.