fix(launcher): close LA4 review findings

src/AcDream.Launcher.Core/Orchestration/LauncherExecutableSet.cs

@@ -4,20 +4,59 @@ using AcDream.Launcher.Core.Profiles;
 namespace AcDream.Launcher.Core.Orchestration;
 
 /// <summary>
-/// Host executable paths supplied by the current installation. LA10 will
-/// resolve these from the versioned <c>app/current</c> pointer; LA4 keeps the
-/// mapping injectable and host-agnostic.
+/// Resolves and validates the co-deployed graphical/headless hosts. LA10 will
+/// replace the directory lookup with its versioned-current resolver; until
+/// then a missing host disables the corresponding action instead of deferring
+/// failure until process creation.
 /// </summary>
-public sealed record LauncherExecutableSet(
-    string GraphicalHostPath,
-    string HeadlessHostPath,
-    string? WorkingDirectory = null)
+public sealed class LauncherExecutableSet
 {
+    private readonly Func<string, bool> _fileExists;
+
+    public LauncherExecutableSet(
+        string graphicalHostPath,
+        string headlessHostPath,
+        string? workingDirectory = null,
+        Func<string, bool>? fileExists = null)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(graphicalHostPath);
+        ArgumentException.ThrowIfNullOrWhiteSpace(headlessHostPath);
+        GraphicalHostPath = graphicalHostPath;
+        HeadlessHostPath = headlessHostPath;
+        WorkingDirectory = workingDirectory;
+        _fileExists = fileExists ?? File.Exists;
+    }
+
+    public string GraphicalHostPath { get; }
+
+    public string HeadlessHostPath { get; }
+
+    public string? WorkingDirectory { get; }
+
+    public LauncherCapability GetAvailability(LaunchMode mode)
+    {
+        string path = mode == LaunchMode.Headless
+            ? HeadlessHostPath
+            : GraphicalHostPath;
+        if (_fileExists(path))
+        {
+            return LauncherCapability.Available;
+        }
+
+        string host = mode == LaunchMode.Headless
+            ? "headless host"
+            : "graphical client";
+        return LauncherCapability.Unavailable(
+            $"The co-deployed {host} is missing at '{path}'. Reinstall or update "
+            + "the client before launching.");
+    }
+
     public LauncherProcessSpec CreatePlaySpec(
         LaunchMode mode,
         string configFilePath)
     {
         ArgumentException.ThrowIfNullOrWhiteSpace(configFilePath);
+        RequireAvailable(mode);
 
         return mode == LaunchMode.Headless
             ? new LauncherProcessSpec(
@@ -33,6 +72,7 @@ public sealed record LauncherExecutableSet(
     public LauncherProcessSpec CreateProbeSpec(string configFilePath)
     {
         ArgumentException.ThrowIfNullOrWhiteSpace(configFilePath);
+        RequireAvailable(LaunchMode.Headless);
         return new LauncherProcessSpec(
             HeadlessHostPath,
             ["--config", configFilePath],
@@ -49,4 +89,14 @@ public sealed record LauncherExecutableSet(
             Path.Combine(fullDirectory, "acdream-headless" + executableSuffix),
             fullDirectory);
     }
+
+    private void RequireAvailable(LaunchMode mode)
+    {
+        LauncherCapability capability = GetAvailability(mode);
+        if (!capability.IsAvailable)
+        {
+            throw new LauncherOperationException(
+                capability.Reason ?? "The selected launcher host is unavailable.");
+        }
+    }
 }