Stufe 2 (#764): Einmal-Anmeldung fuer die Huelle ueber den Manager-Socket

Der Manager hoert zusaetzlich auf einem lokalen Socket (0600 bzw. Pipe nur
fuer den eigenen Benutzer). Dort gibt es nur /api/shell/*, ueber TCP gibt
es diese Pfade nicht. Ein Einmal-Code (256 Bit, einmal, hoechstens 60 s)
wird in der WebUI aus dem Fragment gegen das Token getauscht und sofort
aus der Adresse entfernt. Tests: zweimal, zu spaet, ueber TCP - alle
scheitern.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/ClawdDotNet.Core/Instances/InstanceEndpoint.cs

@@ -121,7 +121,7 @@ public static class InstanceEndpoint
         ClearStaleFile(McpSocketPath(instanceDirectory));
     }
 
-    private static void ClearStaleFile(string path)
+    internal static void ClearStaleFile(string path)
     {
         try
         {
@@ -152,7 +152,7 @@ public static class InstanceEndpoint
         RestrictFile(McpSocketPath(instanceDirectory));
     }
 
-    private static void RestrictFile(string path)
+    internal static void RestrictFile(string path)
     {
         if (OperatingSystem.IsWindows()) return;
 
@@ -185,7 +185,7 @@ public static class InstanceEndpoint
     public static HttpMessageHandler CreateHandler(string instanceDirectory)
         => CreateHandler(SocketPath(instanceDirectory), PipeName(instanceDirectory));
 
-    private static HttpMessageHandler CreateHandler(string socketPath, string pipeName)
+    internal static HttpMessageHandler CreateHandler(string socketPath, string pipeName)
     {
         if (OperatingSystem.IsWindows())
         {
@@ -239,7 +239,7 @@ public static class InstanceEndpoint
     /// müssen denselben Pipenamen ergeben. Unter Linux sind es zwei Verzeichnisse und
     /// dürfen es nicht.</para>
     /// </summary>
-    private static string Fingerprint(string instanceDirectory)
+    internal static string Fingerprint(string instanceDirectory)
     {
         var full = Path.GetFullPath(instanceDirectory).TrimEnd(
             Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar);

src/ClawdDotNet.Core/Instances/ManagerEndpoint.cs

@@ -0,0 +1,46 @@
+namespace ClawdDotNet.Core.Instances;
+
+/// <summary>
+/// #764: The instance manager's local socket — the way the shell (ClawdDotNet.Shell) talks to
+/// it without the web access token.
+///
+/// <para><b>Why a socket and not the web port.</b> The shell opens the web interface signed in,
+/// through a one-time code. Asking for that code must prove that the asker is the user who runs
+/// the manager on this machine — not anybody who reaches the port. The file system says that:
+/// the socket is 0600 (Linux) or a pipe for the current user only (Windows), exactly like the
+/// instance socket (<see cref="InstanceEndpoint"/>). Over TCP the shell endpoints do not exist.</para>
+///
+/// <para>It lives next to <c>manager.json</c>: the shell finds the manager the same way it finds
+/// its port.</para>
+/// </summary>
+public static class ManagerEndpoint
+{
+    public const string SocketFileName = "manager-shell.sock";
+
+    public static string SocketPath(string configDirectory)
+        => Path.Combine(Path.GetFullPath(configDirectory), SocketFileName);
+
+    /// <summary>Pipe names are machine-wide; a fingerprint of the folder keeps two installations apart.</summary>
+    public static string PipeName(string configDirectory)
+        => "clawd-manager-" + InstanceEndpoint.Fingerprint(configDirectory);
+
+    public static HttpClient CreateClient(string configDirectory)
+        => new(InstanceEndpoint.CreateHandler(SocketPath(configDirectory), PipeName(configDirectory)))
+        {
+            BaseAddress = new Uri("http://manager")
+        };
+
+    /// <summary>A socket file left by a hard end would block the next bind (see <see cref="InstanceEndpoint.ClearStale"/>).</summary>
+    public static void ClearStale(string configDirectory)
+    {
+        if (OperatingSystem.IsWindows()) return;
+        InstanceEndpoint.ClearStaleFile(SocketPath(configDirectory));
+    }
+
+    /// <summary>0600 after binding; on Windows the pipe's CurrentUserOnly carries the same promise.</summary>
+    public static void Restrict(string configDirectory)
+    {
+        if (OperatingSystem.IsWindows()) return;
+        InstanceEndpoint.RestrictFile(SocketPath(configDirectory));
+    }
+}