[release/9.0-rc2] [Blazor] Update WebAssembly.DevServer to serve the Blazor-Environment header
#57974
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Backport of #57971 to release/9.0-rc2
/cc @MackinnonBuck
[Blazor] Update
WebAssembly.DevServerto serve theBlazor-EnvironmentheaderFixes a recent regression that caused Blazor WebAssembly Standalone apps to always interpret the ASP.NET Core environment as "Production" during development.
Description
Blazor WebAssembly apps determine the ASP.NET Core environment by reading the
Blazor-Environmentheader in the response for the boot manifest (blazor.boot.json). A recent change caused the WebAssembly development server to stop serving this header, which resulted inIWebAssemblyHostEnvironment.Environmentalways returning"Production". This PR fixes the issue by updating the development server to correctly serve the header.Fixes #57941
Customer Impact
Without this fix, customers relying on
IWebAssemblyHostEnvironmentto selectively enable features based on the environment will experience problems during development. They will need to find another solution to determine whether the app is running in a development environment.Regression?
Regressed in .NET 9 Preview 6
Risk
The fix is straightforward, and automated tests now validate the expected behavior.
Verification
Packaging changes reviewed?