Add HTTP transport for WebAssembly test hosts

[Evangelink]

WebAssembly test hosts cannot connect to the named-pipe transport currently used by dotnet test. Microsoft.Testing.Platform now supports the existing dotnettestcli binary protocol over authenticated HTTP, so the SDK needs a matching gateway to enable browser and WASI test execution.

Summary

• host a unique authenticated loopback HTTP endpoint for each WebAssembly test application
• route the existing protocol frames through the normal dotnet test handlers without changing the wire contract
• preserve named pipes for desktop test applications
• support browser CORS and Private Network Access preflight
• keep the endpoint and bearer token out of process arguments by using an atomically owner-only response file
• skip WebAssembly artifact post-processing until a browser-aware merge host exists
• add a Blazor WebAssembly MSTest probe that documents the remaining browser lifecycle integration

The HTTP path is covered both at the gateway boundary and end-to-end with a real MTP application reporting a passing test through dotnet test. The remaining Blazor-specific work is for Blazor Gateway to consume the bootstrap response file, launch the browser, and provide those values to MTP inside the page.

Validation

• focused HTTP gateway, launch, protocol negotiation, desktop pipe, WASI/browser selection, and artifact-processing tests
• end-to-end dotnet test execution through the MTP HTTP client
• focused Blazor WebAssembly sample build test

Related to #54091

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[Copilot]

Pull request overview

Adds an authenticated loopback HTTP transport path for dotnet test when executing WebAssembly (browser/WASI) test hosts, allowing the existing dotnettestcli binary protocol frames to be routed through the current handlers while preserving named pipes for desktop scenarios.

Changes:

• Introduces HttpTestHostGateway (authenticated HTTP + CORS/PNA preflight) and ProtocolMessageSerializer to round-trip protocol frames over HTTP.
• Updates TestApplication to select HTTP vs named-pipe transport based on the module runtime identifier, and writes bootstrap arguments (endpoint + token) to an owner-only response file.
• Adds targeted regression coverage (gateway behavior, transport selection, response-file redaction/permissions/cleanup, artifact post-processing skip for WASM) plus a Blazor WASM MSTest “probe” asset and build test.

Show a summary per file

File	Description
test/TestAssets/TestProjects/DotnetTestDevices/Program.cs	Detects whether the HTTP transport was selected (including via response file) for device-orchestration test coverage.
test/TestAssets/TestProjects/DotnetTestDevices/DotnetTestDevices.csproj	Adds a test-only hook to force a browser-wasm RID to exercise HTTP transport selection.
test/TestAssets/TestProjects/BlazorWasmTestApp/wwwroot/index.html	Adds minimal host page for the Blazor WASM probe asset.
test/TestAssets/TestProjects/BlazorWasmTestApp/SampleTests.cs	Adds a basic MSTest test that asserts it’s running in browser-wasm.
test/TestAssets/TestProjects/BlazorWasmTestApp/README.md	Documents current limitations and expected future Blazor lifecycle integration for dotnet test.
test/TestAssets/TestProjects/BlazorWasmTestApp/Program.cs	Sets up a Blazor WASM app with a test runner service.
test/TestAssets/TestProjects/BlazorWasmTestApp/Pages/Home.razor	Runs tests on startup and displays pass/fail status + exit code.
test/TestAssets/TestProjects/BlazorWasmTestApp/BrowserTestRunner.cs	Runs MTP + MSTest in-process within the browser app.
test/TestAssets/TestProjects/BlazorWasmTestApp/BlazorWasmTestApp.csproj	New Blazor WASM test app asset configured to run MSTest/MTP in browser-wasm.
test/TestAssets/TestProjects/BlazorWasmTestApp/App.razor	Minimal router for the Blazor WASM probe asset.
test/TestAssets/TestProjects/BlazorWasmTestApp/_Imports.razor	Razor imports for the probe asset.
test/Microsoft.NET.Sdk.BlazorWebAssembly.Tests/VanillaWasmTests.cs	Adds a build-only test validating the new Blazor WASM probe asset builds.
test/dotnet.Tests/CommandTests/Test/TestApplicationLaunchTests.cs	Adds transport-selection tests (HTTP for WASM, pipes for desktop) and response-file redaction/permissions/cleanup assertions.
test/dotnet.Tests/CommandTests/Test/HttpTestHostGatewayTests.cs	Adds unit tests covering authenticated frame dispatch, CORS/PNA preflight behavior, and malformed/corrupt frame handling.
test/dotnet.Tests/CommandTests/Test/GivenDotnetTestSelectsDevice.cs	Adds an end-to-end device-orchestration test asserting HTTP transport selection.
test/dotnet.Tests/CommandTests/Test/ArtifactPostProcessingManagerTests.cs	Adds coverage for skipping artifact post-processing for WASM modules.
src/Cli/dotnet/Commands/Test/MTP/TestApplication.cs	Switches between pipe vs HTTP transport; creates owner-only bootstrap response file; redacts args for logging; disables control channel for HTTP.
src/Cli/dotnet/Commands/Test/MTP/IPC/ProtocolMessageSerializer.cs	Extracts frame serialize/deserialize logic for reuse by HTTP gateway.
src/Cli/dotnet/Commands/Test/MTP/IPC/HttpTestHostGateway.cs	New HTTP listener that authenticates via bearer token and forwards protocol frames (with CORS/PNA support).
src/Cli/dotnet/Commands/Test/MTP/ArtifactPostProcessingManager.cs	Skips artifact post-processing for WASM modules until a browser-aware merge host exists.
src/Cli/dotnet/Commands/Test/CliConstants.cs	Adds new CLI constants for the HTTP transport and bootstrap options.

Copilot's findings

• Files reviewed: 21/21 changed files
• Comments generated: 1

[Evangelink]

/ba-g #54914

[pavelsavara]

Is this going to work with <Project Sdk="Microsoft.NET.Sdk.WebAssembly"> ?
Also maybe it would be good to talk about the design with us ?