advertising manifest cannot be loaded

My machine doesn't have access to nuget.org.

```bash
rich@Mac dotnet-inspect % sudo dotnet workload restore prototypes/inspect-web/engine/InspectWeb.Engine.csproj
Password:

Welcome to .NET 11.0!
---------------------
SDK Version: 11.0.100-preview.7.26381.103

Telemetry
---------
The .NET tools collect usage data in order to help us improve your experience. It is collected by Microsoft and shared with the community. You can opt-out of telemetry by setting the DOTNET_CLI_TELEMETRY_OPTOUT environment variable to '1' or 'true' using your favorite shell.

Read more about .NET CLI Tools telemetry: https://aka.ms/dotnet-cli-telemetry

----------------
Installed an ASP.NET Core HTTPS development certificate.
To trust the certificate, run 'dotnet dev-certs https --trust'
Learn about HTTPS: https://aka.ms/dotnet-https

----------------
Write your first app: https://aka.ms/dotnet-hello-world
Find out what's new: https://aka.ms/dotnet-whats-new
Explore documentation: https://aka.ms/dotnet-docs
Report issues and find source on GitHub: https://github.com/dotnet/core
Use 'dotnet --help' to see available commands or visit: https://aka.ms/dotnet-cli
--------------------------------------------------------------------------------------

Failed to update the advertising manifest microsoft.net.workloads: Unable to load the service index for source https://api.nuget.org/v3/index.json..
No workload update found.
No workloads installed for this feature band. To update workloads installed with earlier SDK versions, include the --from-previous-sdk option.
Garbage collecting for SDK feature band(s) 9.0.300 10.0.300 11.0.100-preview.1 11.0.100-preview.2 11.0.100-preview.3 11.0.100-preview.4 11.0.100-preview.5 11.0.100-preview.6 11.0.100-preview.7...

Successfully updated workload(s): .

Build started 8/14/2026 4:47:36 PM.

Build succeeded.
0 Warning(s)
0 Error(s)

Time Elapsed 00:00:00.63
Installing workloads: wasm-tools

Workload installation failed. Rolling back installed packs...
Workload installation failed: One or more errors occurred. (Unable to load the service index for source https://api.nuget.org/v3/index.json.) (Unable to load the service index for source https://api.nuget.org/v3/index.json.) (Unable to load the service index for source https://api.nuget.org/v3/index.json.) (Unable to load the service index for source https://api.nuget.org/v3/index.json.) (Unable to load the service index for source https://api.nuget.org/v3/index.json.) (Unable to load the service index for source https://api.nuget.org/v3/index.json.) (Unable to load the service index for source https://api.nuget.org/v3/index.json.) (Unable to load the service index for source https://api.nuget.org/v3/index.json.) (Unable to load the service index for source https://api.nuget.org/v3/index.json.) (Unable to load the service index for source https://api.nuget.org/v3/index.json.) (Unable to load the service index for source https://api.nuget.org/v3/index.json.)
rich@Mac dotnet-inspect %
```

Start by reproducing the reported `sudo dotnet workload restore prototypes/inspect-web/engine/InspectWeb.Engine.csproj` command on a machine without access to nuget.org. Trace the advertising manifest update and wasm-tools installation paths; done means the restore behavior and error handling are covered for this offline-source scenario.

Written by the indexing model from the issue text.