[Blazor] Aspire integration improvements

[javiercn]

This issue tracks the work to integrate Blazor applications with Aspire, enabling Blazor apps to benefit from Aspire's orchestration, service discovery, telemetry, and configuration capabilities.

Overview

The integration provides first-class support for all Blazor hosting models (WebAssembly, Server, and Blazor Web) within .NET Aspire applications, using a Backend-for-Frontend (BFF) pattern via a Blazor Gateway component.

Key Features

Blazor Gateway provides:

• Optimized serving of WebAssembly static assets with MapStaticAssets (compression & caching)
• API proxying to backend services (eliminates CORS requirements)
• Configuration flow to WebAssembly clients via /_blazor/_configuration
• Session affinity for multi-replica Blazor Server scenarios
• Replacement for the Dev Server in both development and production

Hosting Scenarios

Scenario	Gateway Configuration
Standalone WebAssembly + Aspire	Separate node (defined in AppHost)
Hosted WebAssembly	Embedded in host project
Blazor Server (single replica)	Not required
Blazor Server (multi-replica)	Separate node (load balancing + session affinity)
Blazor Web (Server + WASM)	Embedded or separate (based on replica count)

Related Work Items

• Server-side configuration endpoint for Blazor Web ([Blazor] Provide the ability to flow configuration from the host to the browser #30116)
• IHostedService support in WebAssembly (Support hosted services in WebAssemblyHost #63637)
• Environment variables in IConfiguration by default ([Blazor] Add environment variables to IConfiguration by default in WebAssemblyHostBuilder #64576)
• Gateway package for standalone Blazor WebAssembly ([Blazor] Gateway package for standalone Blazor WebAssembly applications #64573)
• WebAssembly service defaults template ([Blazor] WebAssembly service defaults template for Aspire integration #64574)
• Consider enabling MetricsSupport/EventSourceSupport by default ([Blazor] Consider enabling MetricsSupport and EventSourceSupport by default for WebAssembly #64575)
• Register Components metric and tracing by default on webassembly host ([Blazor] Register Components metric and tracing by default on webassembly host. #64736)