Agents window: PR changes not updated

### Description

The PR changes show an outdated list of files:

Some files are no longer in the changed files. E.g., the first one doesn't have any changes anymore and the combined diff editor seems to fall back to show the entire file.

The PR extension shows the updated file list in the Editor window:

### Issue Details

Item|Value
---|---
Issue Category|Bug
Target|Agents Window
VS Code Version|Code - Insiders 1.137.0-insider (94b021b519e8e3e99777a1ff72c77e32e0d4b1d3, 2026-09-07T01:46:17Z)
OS Version|Darwin arm64 25.6.0

System Info

Item|Value
---|---
VS Code Version|Code - Insiders 1.137.0-insider (94b021b519e8e3e99777a1ff72c77e32e0d4b1d3, 2026-09-07T01:46:17Z)
OS Version|Darwin arm64 25.6.0
CPUs|Apple M1 Max (10 x 2400)
GPU Status|2d_canvas: enabled
GPU0: VENDOR= 0x106b [Google Inc. (Apple)], DEVICE=0x0000 [ANGLE (Apple, ANGLE Metal Renderer: Apple M1 Max, Version 26.6.2 (Build 25G83))], DRIVER_VENDOR=Apple, DRIVER_VERSION=26.6.2 *ACTIVE*
Machine model name: MacBookPro
Machine model version: 18.2
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: enabled_on
trees_in_viz: disabled_off
video_decode: enabled
video_encode: enabled
webgl: enabled
webgpu: enabled
webnn: disabled_off
Load (avg)|12, 22, 26
Memory (System)|64.00GB (0.07GB free)
Process Argv|--log trace --log github.copilot-chat=debug --crash-reporter-id 7aad610c-0e6b-48aa-ba87-b704b1b543cf
Screen Reader|no
VM|0%
User Agent|Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Code-Insiders/1.137.0-insider Chrome/148.0.7778.280 Electron/42.10.0 Safari/537.36
Installation pure|true

Extensions (10)

Name|Identifier|Author|Version
---|---|---|---
ESLint|dbaeumer.vscode-eslint|dbaeumer|3.0.34
Prettier - Code formatter|esbenp.prettier-vscode|esbenp|12.4.0
GitHub Pull Requests|github.vscode-pull-request-github|GitHub|0.165.2026090413
German Language Pack for Visual Studio Code|ms-ceintl.vscode-language-pack-de|MS-CEINTL|1.131.2026090407
Pseudo Language Language Pack|ms-ceintl.vscode-language-pack-qps-ploc|MS-CEINTL|1.131.2026090407
Jupyter Keymap|ms-toolsai.jupyter-keymap|ms-toolsai|1.1.2
Remote Development|ms-vscode-remote.vscode-remote-extensionpack|ms-vscode-remote|0.26.0
VS Code Team Tools|ms-vscode.vscode-team-tools|ms-vscode|0.1.2026090401
XML|redhat.vscode-xml|redhat|0.29.2026090408
Code Spell Checker|streetsidesoftware.code-spell-checker|streetsidesoftware|4.7.3

Theme extensions: 9

A/B Experiments

```
vsliv368:30146709
pythonvspyt551cf:31249598
nativeloc1:31118317
dwcopilot:31158714
471b6256:31240254
dwoutputs:31242946
copilot_t_ci:31333650
g012b348:31231168
pythonrdcb7:31268811
pythonpcpt1cf:31399617
6518g693:31302842
envsactivate1:31349248
editstats-enabled:31346256
cloudbuttont:31366566
3efgi100_wstrepl:31403338
cp_cls_t_966_ss:31526232
4je02754:31565972
8hhj4413:31478653
ge8j1254_inline_auto_hint_haiku:31490507
cp_cls_c_1081:31454833
conptydll_true:31485575
e9c30283:31453065
c9b86496:31447327
ei9d7968:31462942
89g7j272:31506658
hhf17803:31462392
i2gc6536:31472020
52612955:31508042
h08i8180:31475367
23c7c724:31520045
ddid_t:31478204
hmra_i5g22:-9
7df3h592:31491241
cp_cls_t_1082:31535311
logging_enabled_new:31490725
jb_cp_cls_t_632:31543129
32d76977:31503652
ha629193:31508444
nes-vscode-team-custom-3:31566788
a1ije391_t:31533808
jbcp_cls_pctr_t:31531130
3f904173:31522231
cp_intellij_t_nes:31548657
gf14b233:31526830
hide-eh-duplicates:31533831
ihg5j128:31534457
b1c25fc8:31539904
sandbox-ui-on-2:31543161
e6afd895:31554864
90g4a790:31550158
enable_editor_pane_layout:31551200
52258b4d:31547953
36h42362:31560305
c7c27ce7:31551212
voicemodeon:31569056
a81hg326:31566732
1h923230:31564177
1532g621_copy:31554310
sol_fast:31574408
treatment-23-1:31555779
unuse_dynamic_mcp:31555281
0c1h4866:31562347
vrbsty_fls:31561057
a3a5c856:31566206
multi-root-copilot-claude:31576062
5b8j3302:31564600
autotiers:31569070
mangle-name-treatment:31568054
allow-signed-out:31574470
codex-agent-enabled:31566739
64a8d082:31573709
issue8950-5d26a188:31574957
multiv2:31574987
ae8b2313:-9
2bfb8b39:31576696
enable-sandbox:31578383
new-session-original:31578499
shell-tool-scripts:31578439
permission_prompt_treatment:1294978
ccr_pr_nudge_adoption:1319471
vsc_wsm_t:1324223
eh853263:1370294
auto_mode_control:1367906
h5e14506:1348996
ce50c479:1367875
```