GitHub Copilot inline completions fail for every C# file in a Unity 6 workspace

Type: Bug

## Description

GitHub Copilot inline completions do not appear for any C# file in one Unity project. Copilot Chat is installed, running, and signed in. Inline completions work in other projects using the same VS Code installation and account.

The active files are correctly identified as C# in VS Code. Running `Trigger Inline Suggestion` has no visible effect.

The GitHub Copilot output contains:

2026-09-06 15:26:39.057 [info] ccreq:035adfbb.copilotmd | markdown

The same `copilotmd | markdown` request label appears when explicitly running `Trigger Inline Suggestion`.

## Environment

- macOS
- VS Code stable
- GitHub Copilot Chat: 0.64.1
- C# Dev Kit: 3.20.199
- C# extension: 2.140.9
- Visual Studio Tools for Unity: 1.3.1
- Unity: 6000.2.10f1
- Project type: Unity C# project
- Project solution: generated `.slnx`
- Project file: generated `Assembly-CSharp.csproj`

## Reproduction

1. Open the Unity repository in VS Code.
2. Open any `.cs` file under `Assets`.
3. Confirm the language mode is `C#`.
4. Add an incomplete statement, for example:

`Vector3 nextPosition =`

5. Run `Trigger Inline Suggestion`.
6. No inline completion appears.
7. Repeat with a second C# file in the same repository. The result is the same.

## Expected behavior

Copilot should display an inline completion in the C# editor.

## Troubleshooting performed

- Confirmed GitHub Copilot Chat is installed and running.
- Confirmed the GitHub account is signed in.
- Confirmed inline suggestions are enabled.
- Confirmed the workspace is trusted.
- Confirmed the files are classified as C#.
- Deleted the VS Code workspace storage directory.
- Reloaded and restarted the extension host.
- Disabled Visual Studio Tools for Unity for the workspace.
- Opened the repository directly as a folder.
- Deleted and regenerated the Unity solution and project files.
- Tested multiple C# files, including both tracked and untracked files.
- Checked for `.copilotignore`, `.gitignore`, `.gitattributes`, and workspace settings that could exclude the files.
- No repository-level Copilot exclusion was found.
- Inline completions work in other projects in the same VS Code installation.

## Additional observation

The Copilot log identifies the request as `copilotmd | markdown`, even though the active editor document is correctly identified as C#. It is unclear whether this is normal internal telemetry or indicates that the C# inline-completion provider is routing through the wrong provider.

Please advise whether Unity 6 generated projects using C# Dev Kit and Visual Studio Tools for Unity are currently supported for Copilot inline completions, and whether the `copilotmd | markdown` request path is expected for `Trigger Inline Suggestion`.

VS Code version: Code 1.136.1 (a44adf7f53e00964ab890f9f8758a334f1fc15bc, 2026-09-03T05:06:41Z)
OS version: Darwin arm64 25.6.0
Modes:

System Info

|Item|Value|
|---|---|
|CPUs|Apple M3 Pro (11 x 2400)|
|GPU Status|2d_canvas: enabled
GPU0: VENDOR= 0x106b [Google Inc. (Apple)], DEVICE=0x0000 [ANGLE (Apple, ANGLE Metal Renderer: Apple M3 Pro, Version 26.6.2 (Build 25G83))], DRIVER_VENDOR=Apple, DRIVER_VERSION=26.6.2 *ACTIVE*
Machine model name: Mac
Machine model version: 15.6
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, 2|
|Memory (System)|18.00GB (0.12GB free)|
|Process Argv|/Users/aeonamberwood/Documents/GitHub/Cert4-AI-Weekly -g /Users/aeonamberwood/Documents/GitHub/Cert4-AI-Weekly/Assets/Weekly Material/Week 8/Scripts/BlobAI.cs:1:0 --crash-reporter-id 9ffc9361-3f1f-4364-9fef-c404fd466d0e|
|Screen Reader|no|
|VM|0%|
Extensions (4)

Name|Identifier|Author|Version
---|---|---|---
godot-tools|geequlim.godot-tools|geequlim|2.7.1
C# Dev Kit|ms-dotnettools.csdevkit|ms-dotnettools|3.20.199
C#|ms-dotnettools.csharp|ms-dotnettools|2.140.9
.NET Install Tool|ms-dotnettools.vscode-dotnet-runtime|ms-dotnettools|3.1.0

A/B Experiments

```
vsliv368:30146709
binariesv615:30325510
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
diffpatch-lysithea-24-production:31579162
cp_cls_t_966_ss:31526232
4je02754:31572277
c3h7c220:31478652
ge8j1254_inline_auto_hint_haiku:31490510
cp_cls_c_1081:31454833
conptydll_true:31498968
e9c30283:31461165
46204921:31447328
control_6dc23131:31576178
ei9d7968:31496641
chat:31457767
8hig5102:31480529
89g7j272:31518289
i2gc6536:31499202
52612955:31516516
h08i8180_copy:31475368
ddid_t:31478206
hmra_i5g22:31518061
m11_d0di3990:31575057
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
d7b18187:31526828
ahp-both-windows:31556933
ihg5j128:31534457
9gg7f176:31542112
sandbox-ui-on-2:31543161
enable_editor_pane_layout:31569726
allow-none:31555437
ac562147:31564510
c7c27ce7:31554789
1h923230:31564177
0dg73464:31554319
treatment-23-1:31555779
unuse_dynamic_mcp:31555281
0d8dfbc3:31570291
a1hcc538:31559322
0c1h4866:31566224
vrbsty_fls:31561059
session-archive:31558132
5b8j3302:31564601
mangle-name-treatment:31572634
39a5d156:31574986
2bfb8b39:31576696
permission_prompt_treatment:1332566
ccr_pr_nudge_control:1319470
vsc_wsm_c:1340633
jidc7660:1370295
auto_mode_control:1367906
h5e14506:1348996
1g5a5742:1379227

```