Add .webmanifest MIME type to Wasm.web.config for PWA support on Azure

[Copilot]

Blazor WebAssembly PWA apps deployed to Azure fail to load manifest.webmanifest with 404 errors, preventing PWA installation. The IIS web.config lacks MIME type mapping for .webmanifest files.

Changes:

• Added <remove fileExtension=".webmanifest" /> and <mimeMap fileExtension=".webmanifest" mimeType="application/manifest+json" /> to src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Wasm.web.config

The MIME type application/manifest+json follows the W3C Web App Manifest specification. Pattern matches existing file extension handling in the config (.json, .wasm, etc.).

Original prompt

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This section details on the original issue you should resolve

<issue_title>Missing Manifest after azure deploy</issue_title>
<issue_description>### Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Vanilla Blazor WebAssembly-App gets started locally on the iis the manifest gets deployed correct. If the Blazor WebAssembly-App gets deployed on azure the manifest gets missing. Browser shows

Manifest fetch from https://-------------------------------.azurewebsites.net/manifest.webmanifest failed, code 404

Because its missing the application can`t start as PWA.

Expected Behavior

Manifest should be there and in correct place

Steps To Reproduce

Create Blazor WebAssembly-App with PWA, deploy to azure

Exceptions (if any)

workaround or fix

.NET Version

10

Anything else?

-</issue_description>

<agent_instructions>Do not build the repo locally, you won't be able to test this feature.

Update
https://github.com/dotnet/runtime/blob/main/src/mono/nuget/Microsoft.NET.Sdk.WebAssembly.Pack/build/Wasm.web.config to include the mime type.

Do not try to build or test, just make the change and send a PR</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Missing Manifest after azure deploy #121931

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[javiercn]

LGTM

/cc: @maraf

[Copilot]

Pull request overview

This PR adds IIS MIME type configuration for .webmanifest files to enable PWA support for Blazor WebAssembly applications deployed to Azure. The change resolves 404 errors that prevent PWA installation when manifest files are not recognized by IIS.

• Added MIME type mapping for .webmanifest files with application/manifest+json following W3C Web App Manifest specification
• Follows existing IIS configuration pattern with <remove> followed by <mimeMap> entries