Cannot download roslyn copilot package when http_proxy env var is set to empty

## Environment data
`dotnet --info` output:

```sh
vscode ➜ /workspaces/dotnet $ dotnet --info
.NET SDK:
 Version:           9.0.302
 Commit:            bb2550b9af
 Workload version:  9.0.300-manifests.fadeff71
 MSBuild version:   17.14.13+65391c53b

Runtime Environment:
 OS Name:     debian
 OS Version:  12
 OS Platform: Linux
 RID:         linux-arm64
 Base Path:   /usr/share/dotnet/sdk/9.0.302/

.NET workloads installed:
There are no installed workloads to display.
Configured to use loose manifests when installing new manifests.

Host:
  Version:      9.0.7
  Architecture: arm64
  Commit:       3c298d9f00

.NET SDKs installed:
  9.0.302 [/usr/share/dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 9.0.7 [/usr/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 9.0.7 [/usr/share/dotnet/shared/Microsoft.NETCore.App]

Other architectures found:
  None

Environment variables:
  Not set

global.json file:
  Not found

Learn more:
  https://aka.ms/dotnet/info

Download .NET:
  https://aka.ms/dotnet/download
```

VS Code version: 

```
Version: 1.103.2 (Universal)
Commit: 6f17636121051a53c88d3e605c491d22af2ba755
Date: 2025-08-20T16:45:34.255Z
Electron: 37.2.3
ElectronBuildId: 12035395
Chromium: 138.0.7204.100
Node.js: 22.17.0
V8: 13.8.500258-electron.0
OS: Darwin arm64 24.6.0
```

C# Extension version: 2.90.51

## C# logs
C# output window contents:

```log
2025-09-01 03:52:45.112 [trace] Activating C# Extension
2025-09-01 03:52:45.112 [info] Installing C# dependencies...
2025-09-01 03:52:45.112 [info] 

2025-09-01 03:52:45.112 [info] Platform: linux, arm64, name=debian, version=12

2025-09-01 03:52:45.112 [info] 

2025-09-01 03:52:45.112 [info] Downloading package 'Language server for Roslyn Copilot integration' 
2025-09-01 03:52:45.112 [info] Failed at stage: downloadPackage

2025-09-01 03:52:45.112 [info] TypeError: Invalid URL

2025-09-01 03:52:45.112 [info] 

2025-09-01 03:52:45.112 [debug] Extension vscode.configuration-editing does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.css-language-features does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.debug-auto-launch does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.debug-server-ready does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.emmet does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.extension-editing does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.git does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.git-base does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.github does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.grunt does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.gulp does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.html-language-features does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.ipynb does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.jake does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.json-language-features does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.markdown-language-features does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.markdown-math does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.merge-conflict does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension ms-vscode.js-debug does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension ms-vscode.vscode-js-profile-table does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.npm does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.php-language-features does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.references-view does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.search-result does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.terminal-suggest does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.tunnel-forwarding does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension vscode.typescript-language-features does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension dbaeumer.vscode-eslint does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension GitHub.copilot does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension GitHub.copilot-chat does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension GitHub.vscode-pull-request-github does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension ms-dotnettools.csdevkit does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension ms-dotnettools.csharp does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [debug] Extension ms-dotnettools.vscode-dotnet-runtime does not contribute csharpExtensionLoadPaths
2025-09-01 03:52:45.112 [trace] C# Extension activated in 33.479ms.
2025-09-01 03:52:45.916 [info] Locating .NET runtime version 9.0.1
2025-09-01 03:52:45.950 [info] Dotnet path: /usr/share/dotnet/dotnet
2025-09-01 03:52:45.950 [info] Activating C# + C# Dev Kit...
2025-09-01 03:52:45.972 [error] Microsoft.CodeAnalysis.LanguageServer client: couldn't create connection to server.
Error: Component DLL not found: /home/vscode/.vscode-server/extensions/ms-dotnettools.csharp-2.90.51-linux-arm64/.roslynCopilot/Microsoft.VisualStudio.Copilot.Roslyn.LanguageServer.dll
    at i0 (/home/vscode/.vscode-server/extensions/ms-dotnettools.csharp-2.90.51-linux-arm64/dist/extension.js:1203:9455)
    at Function.setupDevKitEnvironment (/home/vscode/.vscode-server/extensions/ms-dotnettools.csharp-2.90.51-linux-arm64/dist/extension.js:1208:27174)
    at Function.startServer (/home/vscode/.vscode-server/extensions/ms-dotnettools.csharp-2.90.51-linux-arm64/dist/extension.js:1208:21528)
    at l (/home/vscode/.vscode-server/extensions/ms-dotnettools.csharp-2.90.51-linux-arm64/dist/extension.js:1208:15488)
    at Q3.createConnection (/home/vscode/.vscode-server/extensions/ms-dotnettools.csharp-2.90.51-linux-arm64/dist/extension.js:58:11280)
    at Q3.start (/home/vscode/.vscode-server/extensions/ms-dotnettools.csharp-2.90.51-linux-arm64/dist/extension.js:58:1231)
    at Function.initializeAsync (/home/vscode/.vscode-server/extensions/ms-dotnettools.csharp-2.90.51-linux-arm64/dist/extension.js:1208:16003)
    at oje (/home/vscode/.vscode-server/extensions/ms-dotnettools.csharp-2.90.51-linux-arm64/dist/extension.js:1208:38465)
```

## Steps to reproduce

1. Create a new dev container with the following `devcontainer.json`:

```json
{
    "name": "C# (.NET)",
    "image": "mcr.microsoft.com/devcontainers/dotnet:1-9.0-bookworm",

    "remoteEnv": {
        "HTTP_PROXY": "${localEnv:HTTP_PROXY}",
        "HTTPS_PROXY": "${localEnv:HTTPS_PROXY}"
    },

    "customizations": {
        "vscode": {
	    "extensions": [
        	"ms-dotnettools.csdevkit"
            ]
        }
    }
}
```
2. Make sure your host system does not have HTTP_PROXY/HTTPS_PROXY set (i.e. environment variables needs to be unset).
2. Reopen in dev container and wait for extensions to be installed.
3. Create and open a new `helloworld.cs` file to activate the C# extension.

## Expected  behavior

C# extension activates properly.

## Actual behavior

C# extension fails to activate due to Invalid URL when trying to download the Roslyn Copilot Language Server (see log above for full details):

```log
2025-09-01 03:52:45.112 [info] Downloading package 'Language server for Roslyn Copilot integration' 
2025-09-01 03:52:45.112 [info] Failed at stage: downloadPackage

2025-09-01 03:52:45.112 [info] TypeError: Invalid URL
```

## Additional context

I have tested that if I don't set `HTTP_PROXY` in the dev container, or if `HTTP_PROXY` is set to a valid proxy url, C# extension downloads the package and activates correctly.

Looking at the code, I believe the issue is how the [system proxy url is obtained](https://github.com/dotnet/vscode-csharp/blob/f4c6e443a94e2aa2885d958283f6ddea17e66cd0/src/packageManager/proxy.ts#L21):

```ts
function getSystemProxyURL(requestURL: Url): string | undefined {
    if (requestURL.protocol === 'http:') {
        return process.env.HTTP_PROXY ?? process.env.http_proxy;
    } else if (requestURL.protocol === 'https:') {
        return process.env.HTTPS_PROXY ?? process.env.https_proxy ?? process.env.HTTP_PROXY ?? process.env.http_proxy;
    }

    return undefined;
}

export function getProxyAgent(requestURL: Url, proxy: string, strictSSL: boolean): Agent | undefined {
    const proxyURL = proxy.length > 0 ? proxy : getSystemProxyURL(requestURL);

    if (proxyURL === undefined) {
        return undefined;
    }

    const proxyEndpoint = new URL(proxyURL);

    ...
}
```

The code checks if `HTTP_PROXY` is defined, and if not, returns `undefined` for `getProxyAgent`.  But in my case, my `HTTP_PROXY` is defined, but is an empty string.  The code ends up passing an empty string to `new URL(proxyURL)`, most likely causing the Invalid URL error shown in the logs.

### Why HTTP_PROXY may be set to empty

Certain team members on my team rely on proxy servers to get around restrictive network environments, and thus have `HTTP_PROXY`/`HTTPS_PROXY` set on their machines.  To ensure the dev container can properly run `apt-get` and other commands that require network access, we want to propagate the host's environment variables to the dev container via `removeEnv` configuration in `devcontainer.json`.

The problem is not all team members need to use proxy servers, and thus in those cases `HTTP_PROXY` will be unset in the host system, causing the dev container to set `HTTP_PROXY` to empty.

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Uh oh!

Cannot download roslyn copilot package when http_proxy env var is set to empty #8578

Environment data

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Actual behavior

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Why HTTP_PROXY may be set to empty

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Cannot download roslyn copilot package when http_proxy env var is set to empty #8578

Description

Environment data

C# logs

Steps to reproduce

Expected behavior

Actual behavior

Additional context

Why HTTP_PROXY may be set to empty

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

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