Extract shared HeadlessTerminaFixture for TUI page tests

[Aaronontheweb]

Summary

Three TUI test fixtures duplicate near-identical 28-32-line CreateHeadlessApp helpers that wire up Termina's VirtualTerminal + VirtualInputSource against a ServiceCollection. Extracting a shared generic fixture would let new TUI page tests onboard with a single call instead of copying the boilerplate.

Affected files

• src/Netclaw.Cli.Tests/Tui/InitWizardPageTests.cs:410-441 (CreateHeadlessApp, 32 lines)
• src/Netclaw.Cli.Tests/Mcp/McpToolPermissionsPageTests.cs:305-336 (CreateHeadlessApp, 32 lines)
• src/Netclaw.Cli.Tests/Tui/ApprovalsManagerPageTests.cs:137-164 (CreateHeadlessApp, 28 lines)

The variation between them is purely:

• The route string ("/init", "/mcp-tools", "/approvals")
• The page and view-model types
• The view-model factory's dependencies (some need ProviderDescriptorRegistry, some need DaemonApi, etc.)

Everything else — VirtualTerminal(120, 40), AddSingleton<IAnsiTerminal>, AddTerminaVirtualInput, AddTermina(route, builder => builder.RegisterRoute<TPage, TViewModel>(...)), BuildServiceProvider, GetRequiredService<TerminaApplication> — is identical.

Suggested shape

A generic builder in a shared test-utility location, e.g.:

public static class HeadlessTerminaFixture
{
    public sealed record Result<TViewModel>(
        VirtualTerminal Terminal,
        TerminaApplication App,
        VirtualInputSource Input,
        TViewModel ViewModel);

    public static Result<TViewModel> Build<TPage, TViewModel>(
        string route,
        Func<IServiceProvider, TPage> pageFactory,
        Func<IServiceProvider, TViewModel> viewModelFactory,
        Action<IServiceCollection>? configureServices = null)
        where TPage : class
        where TViewModel : class
    { /* shared body */ }
}

Each existing call site collapses to ~5 lines.

Suggested home

Two candidates:

1. Netclaw.Tests.Utilities — already houses DisposableTempDir and other cross-test helpers. Most discoverable for future page tests outside the CLI tree.
2. src/Netclaw.Cli.Tests/Tui/HeadlessTerminaFixture.cs — keeps it scoped to CLI tests since that's where every current consumer lives.

I'd lean toward option 1 because the next consumer almost certainly will not be in Netclaw.Cli.Tests (e.g., if other projects gain Termina-based UIs) and Netclaw.Tests.Utilities is already designed for this.

Acceptance

• A shared HeadlessTerminaFixture (or equivalent name) callable from any test project.
• The three existing call sites migrated to use it.
• Existing test behavior unchanged: same render assertions, same input sequences, same termination semantics (Ctrl+Q drains the input queue).
• dotnet slopwatch analyze clean.

Out of scope

• Changes to the production pages or Termina library itself.
• Adding new test scenarios — this is a pure refactor.

Discovered during

Audit of PR #927 (netclaw approvals CLI). The /simplify reuse review flagged the 3× duplication after the third copy was added. Deferred to keep the PR's diff focused on the new feature rather than touching unrelated test files.