Fixed: Homebrew’s dotnet silently breaks C# Dev Kit in VSCode
Go-to-definition, find references, and IntelliSense all quit working in VS Code on a .NET 10 project. Syntax highlighting was fine, dotnet build was fine, and the project loaded without complaint. The only sign of trouble was buried in Output > C# Dev Kit:
Using existing .NET runtime at "/opt/homebrew/Cellar/dotnet/10.0.401/libexec/dotnet"
.NET server STDERR: Failed to load .../libhostfxr.dylib, error: dlopen(...):
code signature ... not valid for use in process:
mapping process and mapped file (non-platform) have different Team IDs
.NET server exited with 130
Here’s what’s going on. The Dev Kit language server is signed by Microsoft. Homebrew’s dotnet formula is a Homebrew-built bottle, ad-hoc signed with no Team ID:
$ codesign -dv /opt/homebrew/Cellar/dotnet/10.0.401/libexec/host/fxr/10.0.12/libhostfxr.dylib
Signature=adhoc
TeamIdentifier=not set
macOS won’t load a library into a signed process when the Team IDs don’t match, so the server died on startup every time. No server, no project system—and without that, none of the features that make the extension worth installing.
Where it came from
I never installed it on purpose. I already had .NET from the dotnet-sdk cask, which is a different thing entirely—a cask just runs Microsoft’s official .pkg, so it lands in /usr/local/share/dotnet, properly signed:
Authority=Developer ID Application: Microsoft Corporation (UBF8T346G9)
TeamIdentifier=UBF8T346G9
The formula came in as a dependency:
$ brew uses --installed dotnet
powershell
Installing PowerShell from Homebrew drags in Homebrew’s .NET along with it. And since /opt/homebrew/bin comes first on my PATH, that copy shadowed the good one. Dev Kit found it first.
The fix
Drop the formula. PowerShell was its only dependent, so uninstalling that takes care of both at once:
brew uninstall powershell
# ==> Autoremoving 1 unneeded formula:
# dotnet
Then put PowerShell back as a .NET global tool. It runs on the SDK you already have instead of dragging in a second one:
dotnet tool install --global PowerShell
Verify you’re left with the signed copy:
$ which dotnet
/usr/local/share/dotnet/dotnet
If you actually need Homebrew’s dotnet for something else, leave it alone and point the extensions at the good install in settings.json:
"dotnetAcquisitionExtension.sharedExistingDotnetPath": "/usr/local/share/dotnet/dotnet"
Either way, fully quit and relaunch VS Code afterward. A window reload isn’t enough—the .NET Install Tool caches whichever runtime it resolved.