Keep the npm download out of the pyright tests' time budget

tests/Stampeded.Core.Tests/PythonInterpreterTests.cs

@@ -53,7 +53,7 @@ public void WithoutOneTheAnswerIsWhateverPythonMeansHere()
 	[Test]
 	public async Task AnImportResolvesIntoAnEnvironmentThatIsNotInTheWorktree()
 	{
-		if (LanguageServers.Python() is not { } spec)
+		if (await PythonServer.ResolveAsync() is not { } spec)
 		{
 			Assert.Ignore("no Python language server available");
 			return;

tests/Stampeded.Core.Tests/PythonLspTests.cs

@@ -15,7 +15,7 @@ public class PythonLspTests
 	[Test]
 	public async Task PyrightAnswersDefinitionsAndReferencesAcrossFiles()
 	{
-		if (LanguageServers.Python() is not { } spec)
+		if (await PythonServer.ResolveAsync() is not { } spec)
 		{
 			Assert.Ignore("no Python language server available");
 			return;

tests/Stampeded.Core.Tests/PythonProjectConfigTests.cs

@@ -15,7 +15,7 @@ public class PythonProjectConfigTests
 	[Test]
 	public async Task AProjectConfigNamingItsOwnVenvDoesNotBlindTheReview()
 	{
-		if (LanguageServers.Python() is not { } spec)
+		if (await PythonServer.ResolveAsync() is not { } spec)
 		{
 			Assert.Ignore("no Python language server available");
 			return;

tests/Stampeded.Core.Tests/PythonServer.cs

@@ -0,0 +1,49 @@
+using Stampeded.Core.Infra;
+using Stampeded.Core.Lsp;
+
+namespace Stampeded.Core.Tests;
+
+/// <summary>
+/// The Python language server a test talks to, with its download kept out of the test's own
+/// time budget.
+///
+/// On a machine with node and no pyright, <see cref="LanguageServers.Python"/> answers with
+/// npx, and the first npx start downloads the package from the npm registry before the server
+/// says a word. A test hands one three-minute token to the handshake and its requests, which
+/// is generous for a language server and nothing at all for a registry having a slow morning:
+/// the download alone has been measured at 16 seconds and at 109 seconds on the same runner
+/// image. Every CI runner is fresh, so the first pyright test in a run always paid for it, and
+/// failed with a cancellation inside initialize that named neither the download nor its
+/// duration.
+///
+/// So the download happens here, once per test assembly, under a budget of its own, through
+/// <see cref="ExternalTool.RunAsync"/> - which logs the command with its elapsed time, so a
+/// slow registry shows up as a number in the test output. npx keys its cache on the package
+/// spec, so <c>pyright --version</c> puts the package where <c>pyright-langserver</c> then
+/// finds it. A download that fails or runs out its budget fails every pyright test with that
+/// reason, rather than being skipped: a registry that cannot be reached is a fact about the
+/// run, not about the machine.
+/// </summary>
+static class PythonServer
+{
+	static readonly Lazy<Task> downloaded = new(DownloadAsync);
+
+	/// <summary>The server spec, or null on a machine with no way to run one; for the npx
+	/// form, only after the package is in the npm cache.</summary>
+	public static async Task<LspServerSpec?> ResolveAsync()
+	{
+		if (LanguageServers.Python() is not { } spec)
+			return null;
+		if (spec.Arguments.Contains("--package"))
+			await downloaded.Value;
+		return spec;
+	}
+
+	static async Task DownloadAsync()
+	{
+		using var timeout = new CancellationTokenSource(TimeSpan.FromMinutes(10));
+		await ExternalTool.RunAsync(LanguageServers.OnPath("npx")!,
+			["--yes", "--package", "pyright", "--", "pyright", "--version"],
+			Path.GetTempPath(), timeout.Token);
+	}
+}