Fall back to help when MRU picker cannot run interactively

readme.md

@@ -45,10 +45,11 @@ with smart up-to-date checks of every C# file used to build the app (including
 Every successful `go` / `go dev` invocation records the entry point (local full path or
 remote ref) in a shared history file next to the cache root (`dotnet/go/go.toml`).
 
-With at least one history entry, running with **no arguments** opens an interactive
-picker (searchable, ordered by use count then recency). After you pick an entry you
-can optionally type app arguments (quoted groups supported). With an empty history,
-`dnx go` with no args shows help instead.
+With at least one history entry, running with **no arguments** in an interactive
+terminal opens a searchable picker (ordered by use count then recency). After you
+pick an entry you can optionally type app arguments (quoted groups supported).
+With an empty history, or when stdin is redirected / non-interactive (CI, pipes),
+`dnx go` with no args shows help instead of erroring.
 
 Local paths that no longer exist are dropped from the picker; remote refs stay listed
 even when their download bundle is gone (the next run re-downloads as usual).

src/go/Program.cs

@@ -16,8 +16,9 @@
 app.Add<SkillCommands>();
 
 var prepared = GoArgs.PrepareArgs(args);
-// Zero-arg with no prior runs: show help (same as -h/--help/-?). With history, default command opens the MRU picker.
-if (prepared.Length == 0 && RunHistory.List().Count == 0)
+// Zero-arg: help when history is empty or the console cannot prompt (redirected stdin / non-interactive).
+// With history + an interactive terminal, the default command opens the MRU picker.
+if (prepared.Length == 0 && (RunHistory.List().Count == 0 || !CanPromptInteractively()))
     prepared = ["--help"];
 
 await app.RunAsync(prepared);
@@ -235,15 +236,34 @@ static int CleanArtifacts(string? input, bool all, string? missingInputMessage)
     return AppCleaner.Clean(pdir, stmp, cs);
 }
 
+/// <summary>
+/// True when stdin is a real terminal that can drive Spectre prompts.
+/// Redirected/piped input falls through to help instead of the MRU picker.
+/// </summary>
+static bool CanPromptInteractively()
+{
+    try
+    {
+        if (Console.IsInputRedirected)
+            return false;
+
+        return AnsiConsole.Profile.Capabilities.Interactive;
+    }
+    catch
+    {
+        return false;
+    }
+}
+
 /// <summary>
 /// Interactive MRU picker over go.toml history, then optional app-args prompt.
-/// Returns null on empty history, cancel, or non-interactive console.
+/// Returns null on empty history, cancel, or if prompts cannot run (caller shows help for zero-arg).
 /// </summary>
 static string? TryPickFromHistory(out string[] appArgs)
 {
     appArgs = [];
     var history = RunHistory.List();
-    if (history.Count == 0)
+    if (history.Count == 0 || !CanPromptInteractively())
         return null;
 
     try
@@ -267,8 +287,7 @@ static int CleanArtifacts(string? input, bool all, string? missingInputMessage)
     }
     catch (Exception)
     {
-        // Spectre throws when stdin is redirected / no interactive terminal.
-        ConsoleApp.LogError("Interactive selection requires a terminal.");
+        // Cancelled prompt or unexpected non-interactive environment — no error noise.
         return null;
     }
 }

src/go/help.md

@@ -4,7 +4,7 @@ Usage: [command] [arguments...] [options...] [-h|--help] [--version]
 Runs a file-based .NET app from a .cs entrypoint.
 
 Arguments:
-  [0] <string?>     Path to an existing .cs file or remote ref (owner/repo[@ref][:path]). When omitted, selects from previous runs (MRU) then prompts for optional app args.
+  [0] <string?>     Path to an existing .cs file or remote ref (owner/repo[@ref][:path]). When omitted in an interactive terminal, selects from previous runs (MRU) then prompts for optional app args; otherwise shows help.
   [1] <string[]>    Arguments to pass to the app.
 
 Options: