Windows: Copilot CLI plugin operations fail with “Access is denied” while VS Code is running

### Description

On Windows, Copilot CLI cannot install/uninstall a plugin while VS Code is running. The same command succeeds immediately after all VS Code windows are closed.

Steps to Reproduce
1. Open VS Code, New Chat and New Copilot CLI Session
2. In Github Copilot Cli, run ```/plugin install fabric-skills@fabric-collection```. It fails with such error message: `Failed to install plugin: Failed to install plugin: Access is denied. (os error 5)`
3. Close VS Code, open Copilot Cli in terminal, run same command, it succeeds.

Our extension depends on that plugin and needs to ensure that this dependency is installed and up to date. Requiring users to close VS Code and run commands from a separate terminal significantly disrupts the installation experience.

### Issue Details

Item|Value
---|---
Issue Category|Bug
Target|Visual Studio Code
VS Code Version|Code 1.133.0 (a5b500951314efd502d07465bd138dfbd714a960, 2026-08-11T22:14:08Z)
OS Version|Windows_NT x64 10.0.26200

System Info

Item|Value
---|---
VS Code Version|Code 1.133.0 (a5b500951314efd502d07465bd138dfbd714a960, 2026-08-11T22:14:08Z)
OS Version|Windows_NT x64 10.0.26200
CPUs|12th Gen Intel(R) Core(TM) i9-12900 (24 x 2419)
GPU Status|2d_canvas: enabled
GPU0: VENDOR= 0x10de, DEVICE=0x1ff2 [NVIDIA T400 4GB], DRIVER_VENDOR=NVIDIA, DRIVER_VERSION=32.0.15.9595 *ACTIVE*
GPU1: VENDOR= 0x8086, DEVICE=0x4680 [Intel(R) UHD Graphics 770], DRIVER_VERSION=32.0.101.7085
GPU2: VENDOR= 0x1414, DEVICE=0x008c [Microsoft Basic Render Driver], DRIVER_VERSION=10.0.26100.8875
Machine model name:
Machine model version:
direct_rendering_display_compositor: disabled_off_ok
gpu_compositing: enabled
multiple_raster_threads: enabled_on
opengl: enabled_on
rasterization: enabled
raw_draw: disabled_off_ok
skia_graphite: disabled_off
trees_in_viz: disabled_off
video_decode: enabled
video_encode: enabled
webgl: enabled
webgpu: enabled
webnn: disabled_off
Load (avg)|
Memory (System)|63.70GB (33.17GB free)
Process Argv|--crash-reporter-id 8a9a1e67-5acc-4001-b3e1-6714aa74b0d6
Screen Reader|no
VM|0%
User Agent|Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Code/1.133.0 Chrome/148.0.7778.280 Electron/42.8.0 Safari/537.36
Installation pure|true

A/B Experiments

```
vsliv368:30146709
pythonvspyt551cf:31249601
binariesv615:30325510
nativeloc1:31344060
dwcopilot:31170013
471b6256:31240254
dwoutputs:31242946
copilot_t_ci:31333650
e5gg6876:31282496
pythonrdcb7:31342333
6518g693:31463988
aj953862:31281341
envsactivate1:31551504
cloudbuttont:31379625
3efgi100_wstrepl:31403338
839jf696:31457053
ec5jj548:31422691
metis_rerank_treatment1:31422731
cp_cls_t_966_ss:31526232
4je02754:31466945
c3h7c220:31478652
ge8j1254_inline_auto_hint_haiku:31490510
cp_cls_c_1081:31454833
conptydll_true:31498968
e9c30283:31461165
test_treatment2:31471001
c9b86496:31447327
control_6dc23131:31555649
ei9d7968:31496641
nes-extended-on:31455476
chat:31457767
8hig5102:31480529
89g7j272:31518289
i2gc6536:31499202
52612955:31516516
ghj88844:31499326
ec1eg703:31520046
ddid_t:31478206
hmra_i5g22:-9
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
cdk-lw-on:31524445
a1ije391_t:31540920
hgf2d445:31529595
jbcp_cls_pctr_t:31531130
61138546:31518536
3f904173:31522231
cp_intellij_t_nes:31548657
jf4hg949:31526829
ahp-both-windows:31556933
sessions_5:31532894
ihg5j128:31534457
f412h606:31551416
7g2b5551:31542111
max-result-200:31551155
90g4a790:31556955
5fe6f778:31554331
allow-none:31555437
6i51c363:31551401
ac562147:31564510
c7c27ce7:31554789
a81hg326:31551415
1h923230:31564177
1532g621_copy:31554320
gpt56sol_default:31557530
treatment-23-1:31555779
unuse_dynamic_mcp:31555281
a1hcc538:31559322
ig31j696:31564790
vrbsty_fls:31561059
session-mark-done:31558131
ai4g2856_c:31563074
5b8j3302:31564601
```