x.copilot.instructions.md file, with an & gets HTML encoded to &amp, truncating the instructions.

[ChrisGuzak]

Describe the bug

copilot diagnosed its own bug!

❯ help me figure out why you did not find that automatically, did I
misspell the directory name?

✓ Grep ".github/instructions|instructions.md"
...
✓ List directory ~\source\repos\OSClient.github\instructions
└ 1 file found

● I see the issue now. Looking at my system prompt, I actually was
given the content from osclient-build.instructions.md - it's embedded
at the bottom of my context (starting with the YAML frontmatter
description: "Build workflow for OSClient repository..."). However,
it appears truncated - it cuts off mid-sentence at:

 & $msbuild

So the instructions file was automatically loaded into my context,
but:

 - It got truncated, missing the actual build command parameters
 - Because it was incomplete, I relied on the AGENTS.md file instead
which had more complete instructions

The directory name .github/instructions is correct - no misspelling.
The issue is the automatic injection of that file was truncated
before I could see the full build command.

❯ is there something in that file that caused the trucation?

✓ Read ~\source\repos\OSClient.github\instructions\osclient-build.instr
uctions.md
└ 141 lines read

● Yes! I see the issue. Looking at the injected content in my system
prompt vs the actual file:

In my system prompt, the NuGet restore command shows:

 & {REPO_ROOT}\Src\DeveloperProductivity\UESNugetRestore.ps1

The actual file has:

 & {REPO_ROOT}\Src\DeveloperProductivity\UESNugetRestore.ps1

The & character was HTML-encoded to & during injection. The
truncation happened at line 62 where there's:

 & $msbuild

In my system prompt, I see it just cuts off after & $msbuild without
the rest of the command parameters. The file uses & (PowerShell call
operator) throughout, and something in the injection pipeline is
encoding these as & which may be causing parsing issues or
truncation.

The culprit is likely the & characters - either the HTML encoding is
causing issues, or there's a length limit being hit around that point
in the injection.

❯ what do you suggest? can I update the content to avoid this, using
"." instead? is this a bug in your injection code?

● This is a bug in the injection/rendering pipeline - the & character
is being HTML-encoded to &, and something is causing truncation
around that point.

You can't use . as a replacement - they have different semantics in
PowerShell:

 - & (call operator) - executes an external command or script in a

child scope
- . (dot-sourcing) - runs a script in the current scope, and
doesn't work with executables like MSBuild.exe

Workarounds you could try:

 - Use Start-Process or Invoke-Command:  Start-Process -FilePath

$msbuild -ArgumentList "..." -NoNewWindow -Wait
- Spell out the ampersand: # Use Invoke-Expression (less ideal but
avoids &)
Invoke-Expression "$msbuild /t:Build ..."
- Just use the variable directly (works when no spaces in path):
$msbuild /t:Build ...

However, this is really a bug that should be fixed in the injection
code - the HTML encoding of & to & shouldn't happen for markdown code
blocks, and it definitely shouldn't cause truncation. I'd recommend
filing this as a bug against the Copilot CLI/instructions injection
feature.

Would you like me to help you rewrite the instructions file using one
of these workarounds for now?

Affected version

0.0.392 Commit: cefb35e

Steps to reproduce the behavior

create .github\instructions\foo.instructions.md with contents like this

$vsPath = vswhere.exe -latest -property installationPath
$msbuild = Join-Path $vsPath "MSBuild\Current\Bin\MSBuild.exe"

& $msbuild <path-to-vcxproj> /t:Build /p:Configuration=Debug /p:Platform=x64 /p:UES_SolutionDir=<solution-directory> /v:minimal

the line with & $msbuild ... is the problem as described above.

Expected behavior

expected: these instructions to apply

Additional context

No response

[kawax]

This is a bug that has been present for quite some time where the string is cut off at <.