Chat extension 100% CPU and unresponsive for minutes while idling in large workspace

Type: Performance Issue

Always reproducible. Nothing else installed, also disabled all built-in extensions. This is definitely a Copilot Chat issue. Not doing anything with it or typing, it just appears out of nowehere. It's also shown as `unresponsive` in the "Running extensions" tab. I'm pretty sure this was not an issue a ~1-5 versions back.

This freeze continues for pretty much exactly 3 minutes every time. Depends on the workspace size. In that timeframe, other extensions are largely unresponsive too. For example, the command `Help: Report Performance Issue...` can be selected and run, but no report window appears until the 3 mins freeze is over. As another example, I'm writing something into an output pane from my own extension but it doesn't appear in there until the extension host freeze is over. No extension JS seems to actually run in that duration. The following profile is with no other extensions installed whatsoever:

[CPU-20260916T122139.781Z.cpuprofile.txt](https://github.com/user-attachments/files/32290239/CPU-20260916T122139.781Z.cpuprofile.txt)

About 30 seconds of recording, shortly after enabling the chat extension. The first ~20 seconds, everything was fine. Then the last 10 seconds of the profile the issue started appearing all by itself. Thus, the CPU/freeze problem appears only after 20 seconds or so.

Renderer profile via dev tools, 10s in the middle of the freeze window with nothing else happning:

[Trace-20260916T152548.json.gz](https://github.com/user-attachments/files/32291362/Trace-20260916T152548.json.gz)

VS Code version: Code 1.137.0 (645f29cc3176500b4b5762ba887cf2a7f0ffdf2c, 2026-09-08T13:43:59-07:00)
OS version: Linux arm64 6.8.0-139-generic
Modes: Unsupported

System Info

|Item|Value|
|---|---|
|CPUs|unknown (9 x 0)|
|GPU Status|2d_canvas: disabled_software
GPU0: VENDOR= 0x0000, DEVICE=0x0000
Machine model name:
Machine model version:
direct_rendering_display_compositor: disabled_off_ok
gpu_compositing: disabled_software
multiple_raster_threads: disabled_off
opengl: disabled_off
rasterization: disabled_software
raw_draw: disabled_off_ok
skia_graphite: disabled_off
trees_in_viz: disabled_off
video_decode: disabled_software
video_encode: disabled_software
vulkan: disabled_off
webgl: disabled_off
webgpu: disabled_off
webgpu_on_vk_via_gl_interop: disabled_off
webnn: disabled_off|
|Load (avg)|0, 0, 1|
|Memory (System)|25.15GB (15.12GB free)|
|Process Argv|/home/phi/code --disable-extensions --crash-reporter-id 1cb89cd2-0e7c-4190-b27b-39e38ed4d71c|
|Screen Reader|yes|
|VM|0%|
|DESKTOP_SESSION|xubuntu|
|XDG_CURRENT_DESKTOP|XFCE|
|XDG_SESSION_DESKTOP|xubuntu|
|XDG_SESSION_TYPE|x11|

Process Info

```
CPU % Mem MB PID Process
1 55635198278 173878 code
0 13908799569 173886 zygote
1 83452797416 173986 gpu-process
0 0 173990 broker
0 13908799569 173887 zygote
0 0 173893 zygote
1 132133595909 173961 window [1] (Running Extensions - code - Visual Studio Code)
0 20863199354 173929 utility-network-service
0 41726398708 174006 agent-host
0 55635198278 174100 electron-nodejs (index.js)
0 41726398708 174028 shared-process
0 0 184645 /bin/sh -c /usr/bin/ps -ax -o pid=,ppid=,pcpu=,pmem=,command=
0 111270396555 174029 file-watcher [1]
0 0 174137 gsettings monitor org.gnome.system.proxy
0 111270396555 175774 extension-host [1]
```

Workspace Info

```
| Window (Running Extensions - code - Visual Studio Code)
| Folder (code): more than 20000 files
| File types: class(2824) png(2649) js(2550) h(1993) java(1553) md(1399)
| m(1055) xml(628) json(596) html(414) other(4339)
| Conf files: package.json(203) csproj(18) sln(9) tasks.json(1)
| settings.json(1);
```

Extensions disabled
A/B Experiments

```
vsliv368cf:30146710
binariesv615:30325510
9b8hh234:30694863
nativeloc1:31344060
dwcopilot:31170013
dwoutputs:31242946
copilot_t_ci:31333650
e5gg6876:31282496
pythonrdcb7:31342333
6518g693:31463988
aj953862:31281341
envsactivate1:31551504
gh487529:31544284
cloudbuttont:31379625
3efgi100_wstrepl:31403338
ec5jj548:31422691
cp_cls_t_966_ss:31526232
4je02754:31466945
c3h7c220:31478652
ge8j1254_inline_auto_hint_haiku:31490510
cp_cls_t_1081:31454832
conptydll_true:31498968
e9c30283:31461165
46204921:31447328
ei9d7968:31496641
chat:31457767
8hig5102:31480529
89g7j272:31518289
i2gc6536:31499202
52612955:31516516
ddid_t:31478206
hmra_i5g22:31518061
m11_d0di3990:31580636
7df3h592:31512476
cp_cls_t_1082:31535311
logging_enabled_new:31498466
db5d2638:31499441
jb_cp_cls_t_632:31543129
56dj4588:31512888
32d76977:31512328
ha629193:31508444
a1ije391_t:31540920
jbcp_cls_pctr_t:31531130
cp_intellij_t_nes:31548657
jf4hg949:31526829
ahp-both-windows:31556933
ihg5j128:31534457
7g2b5551:31542111
sandbox-ui-on-2:31543161
enable_editor_pane_layout:31569726
allow-none:31555437
ac562147:31564510
c7c27ce7:31554789
1h923230:31564177
treatment-23-1:31555779
unuse_dynamic_mcp:31555281
0d8dfbc3:31570291
switchtoauto:31559321
0c1h4866:31566224
session-mark-done:31558131
5b8j3302:31564601
autotiers:31584978
mangle-name-control:31572633
signed-out-control:31584138
intellij_nes_preview_t:31580086
39a5d156:31574986
2bfb8b39:31576696
accent:31581110
aw-autom-on:31583758
revealsession_control_7ed7e840:31582193
4ab0b639:31584543
permission_prompt_treatment:1332566
ccr_pr_nudge_control:1319470
vsc_wsm_t:1340632
eh853263:1370294
h5e14506_copy:1348995
1g5a5742:1379227
3aced641:1389836

```

As a side note, the chat extension can't be "enabled". In the running extension tab, you can disable it, but to re-enable, you can't click "enable" in the context menu like with other extensions. You need to first select "Disable AI features", then "Enable AI features" which is pretty counter-intuitive.