Korean IME composition text renders incorrectly in the integrated terminal when Modern UI is enabled

Type: Bug

## Does this issue occur when all extensions are disabled?

Yes

## Steps to Reproduce

1. On macOS, make sure `workbench.experimental.modernUI` is enabled.
2. Open the integrated terminal.
3. Switch to the macOS Korean (2-Set) input method and type Korean at the shell prompt.

## Expected

The Korean text being composed renders at the cursor position.

## Actual

The composition text renders in the wrong place, detached from the cursor.

Turning off `workbench.experimental.modernUI` makes the problem go away. Turning it back on brings it back.

## Recording

## Additional info

- 1.127.0 did not have this problem.
- Also reproduces with the display language set to English.

VS Code version: Code 1.134.0 (Universal) (110a328ea54b42367b803ec53ee0bf52ef26b419, 2026-08-18T18:24:44Z)
OS version: Darwin x64 24.6.0
Modes:

System Info

|Item|Value|
|---|---|
|CPUs|Intel(R) Core(TM) i9-9900K CPU @ 3.60GHz (16 x 3600)|
|GPU Status|2d_canvas: enabled
GPU0: VENDOR= 0x1002, DEVICE=0x67df, DRIVER_VENDOR=AMD, DRIVER_VERSION=15.7.4 *ACTIVE*
GPU1: VENDOR= 0x8086, DEVICE=0x3e98
Machine model name: iMac
Machine model version: 19.1
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)|2, 2, 3|
|Memory (System)|40.00GB (0.57GB free)|
|Process Argv|--enable-proposed-api TabNine.tabnine-vscode --crash-reporter-id 9f4a475a-a66f-4382-9ed1-34a0174541d6|
|Screen Reader|no|
|VM|0%|
Extensions (57)

Name|Identifier|Author|Version
---|---|---|---
Better Comments|aaron-bond.better-comments|aaron-bond|3.0.2
ExtendScript Debugger|adobe.extendscript-debug|Adobe|2.1.0
Bookmarks|alefragnani.bookmarks|alefragnani|14.1.1
Project Manager|alefragnani.project-manager|alefragnani|13.0.1
NuGet Package Manager GUI|aliasadidev.nugetpackagemanagergui|aliasadidev|2.1.1
ShaderlabVSCode|amlovey.shaderlabvscode|amlovey|1.5.1
Claude Code for VS Code|anthropic.claude-code|Anthropic|2.1.246
Dart Data Class Generator|bendixma.dart-data-class-generator|BendixMa|0.5.5
Markdown Preview Mermaid Support|bierner.markdown-mermaid|bierner|1.32.0
MySQL|cweijan.vscode-mysql-client2|cweijan|8.4.5
ESLint|dbaeumer.vscode-eslint|dbaeumer|3.0.24
Git History|donjayamanne.githistory|donjayamanne|0.6.20
GitLens — Git supercharged|eamodio.gitlens|eamodio|19.0.1
EditorConfig|editorconfig.editorconfig|EditorConfig|0.18.2
VSCode Great Icons|emmanuelbeziat.vscode-great-icons|emmanuelbeziat|2.1.120
Prettier - Code formatter|esbenp.prettier-vscode|esbenp|12.4.0
file-icons|file-icons.file-icons|file-icons|1.1.0
Code Runner|formulahendry.code-runner|formulahendry|0.12.2
Kotlin|fwcd.kotlin|fwcd|0.2.36
GitHub 끌어오기 요청|github.vscode-pull-request-github|GitHub|0.162.0
Gemini CLI Companion|google.gemini-cli-vscode-ide-companion|google|0.20.0
Todo Tree|gruntfuggly.todo-tree|Gruntfuggly|0.0.226
Helium Icon Theme|helgardrichard.helium-icon-theme|helgardrichard|1.0.0
ftp-simple|humy2833.ftp-simple|humy2833|0.7.6
Output Colorizer|ibm.output-colorizer|IBM|0.1.2
Unity Code Snippets|kleber-swf.unity-code-snippets|kleber-swf|2.4.0
C# Colors|logerfo.csharp-colors|logerfo|0.2.1
Rainbow CSV|mechatroner.rainbow-csv|mechatroner|3.24.1
Container Tools|ms-azuretools.vscode-containers|ms-azuretools|2.1.0
Docker|ms-azuretools.vscode-docker|ms-azuretools|2.0.0
Korean Language Pack for Visual Studio Code|ms-ceintl.vscode-language-pack-ko|MS-CEINTL|1.131.2026082318
C# 개발자 키트|ms-dotnettools.csdevkit|ms-dotnettools|1.90.2
C#|ms-dotnettools.csharp|ms-dotnettools|2.90.60
.NET Install Tool|ms-dotnettools.vscode-dotnet-runtime|ms-dotnettools|3.1.0
개발 컨테이너|ms-vscode-remote.remote-containers|ms-vscode-remote|0.454.0
Remote - SSH|ms-vscode-remote.remote-ssh|ms-vscode-remote|0.120.0
Remote - SSH: Editing Configuration Files|ms-vscode-remote.remote-ssh-edit|ms-vscode-remote|0.87.0
WSL|ms-vscode-remote.remote-wsl|ms-vscode-remote|0.99.0
원격 개발|ms-vscode-remote.vscode-remote-extensionpack|ms-vscode-remote|0.26.0
Live Preview|ms-vscode.live-server|ms-vscode|0.4.16
원격 탐색기|ms-vscode.remote-explorer|ms-vscode|0.5.0
Remote - Tunnels|ms-vscode.remote-server|ms-vscode|1.5.3
VS Code Speech|ms-vscode.vscode-speech|ms-vscode|0.16.0
Korean (South Korea) language support for VS Code Speech|ms-vscode.vscode-speech-language-pack-ko-kr|ms-vscode|0.5.0
Awesome Flutter Snippets|nash.awesome-flutter-snippets|Nash|4.0.1
Material Icon Theme|pkief.material-icon-theme|PKief|5.37.0
Git File History|pomber.git-file-history|pomber|1.0.1
Thunder Client|rangav.vscode-thunder-client|rangav|2.41.1
YAML|redhat.vscode-yaml|redhat|1.23.0
GitHub Copilot CLI Agents|sbluemin.github-copilot-cli-agents|sbluemin|0.2.7
Code Spell Checker|streetsidesoftware.code-spell-checker|streetsidesoftware|4.5.6
Material Theme (But I Won't Sue You)|t3dotgg.vsc-material-theme-but-i-wont-sue-you|t3dotgg|35.0.3
Ayu|teabyii.ayu|teabyii|1.1.12
Laeyrd|theenggs.laeyrd|TheEnggs|1.1.1
Error Lens|usernamehw.errorlens|usernamehw|3.26.0
Unity|visualstudiotoolsforunity.vstuc|visualstudiotoolsforunity|1.2.2
Markdown All in One|yzhang.markdown-all-in-one|yzhang|3.6.3

A/B Experiments

```
vsliv368cf:30146710
binariesv615:30325510
nativeloc1:31344060
dwcopilot:31170013
dwoutputs:31242946
copilot_t_ci:31333650
e5gg6876:31282496
pythonrdcb7:31342333
6518g693:31463988
aj953862:31281341
envsactivate1:31551504
cloudbuttont:31379625
3efgi100_wstrepl:31403338
ec5jj548:31422691
diffpatch-lysithea-24-production:31573331
cp_cls_t_966_ss:31526232
4je02754:31572277
8hhj4413:31478653
ge8j1254_inline_auto_hint_haiku:31490510
cp_cls_t_1081:31454832
conptydll_true:31498968
e9c30283:31461165
test_treatment2:31471001
46204921:31447328
ei9d7968:31496641
nes-extended-on:31455476
chat:31457767
8hig5102:31480529
89g7j272:31518289
i2gc6536:31499202
52612955:31516516
ddid_t:31478206
hmra_i5g22:31518061
ja75b849:31569110
bjc72774_agent_sandbox:31557830
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
61138546:31518536
cp_intellij_t_nes:31548657
jf4hg949:31526829
ahp-both-windows:31556933
session_8:31532895
ihg5j128:31534457
f412h606:31551416
7g2b5551:31542111
sandbox-ui-on-2:31543161
enable_editor_pane_layout:31569726
allow-none:31555437
6i51c363:31551401
ac562147:31564510
c7c27ce7:31554789
1h923230:31564177
0dg73464:31554319
treatment-23-1:31555779
unuse_dynamic_mcp:31555281
0d8dfbc3:31570291
switchtoauto:31559321
0c1h4866:31566224
vrbsty_fls:31561059
session-archive:31558132
5b8j3302:31564601
mangle-name-treatment:31572634

```