Merge nucleic/lucid-river-toad-6efj into dev

NucleicBroker/IWslc.cs

@@ -15,6 +15,24 @@ public interface IWslc
     /// <summary>Reported in the `hello` capabilities exchange; null when wslc is absent.</summary>
     string? WslcVersion { get; }
 
+    /// <summary>
+    /// What this facade can actually do, merged into the `hello` capabilities so hostd degrades
+    /// instead of discovering the gap at the call site (docs/WINDOWS_PORT.md §2.3, D13). The
+    /// compat SDK alone cannot serve four of them, so a compat-only broker reports none of:
+    /// <list type="bullet">
+    /// <item><c>enumerate</c> — service-backed container enumeration. Without it
+    ///   <c>container.list</c> answers from the broker's OWN roster, so it goes empty across a
+    ///   broker restart and <c>ContainerManager.reconcile</c> sees an empty sandbox.</item>
+    /// <item><c>reattach</c> — re-adopting a running session or container. Without it a broker
+    ///   restart cannot recover the session and <c>session.ensure</c> fails
+    ///   <see cref="WslcError.SessionExists"/>.</item>
+    /// <item><c>tty</c> — pty allocation and resize, i.e. §7's Terminal panel.</item>
+    /// <item><c>stats</c> — per-container resource sampling. Reported when stats are available
+    ///   by ANY means, including the in-guest cgroup read the compat facade falls back to.</item>
+    /// </list>
+    /// </summary>
+    IReadOnlyList<string> Capabilities { get; }
+
     /// <summary>Install the sink BEFORE any operation that can emit events.</summary>
     void SetEvents(IBrokerEvents events);
 
@@ -84,6 +102,16 @@ public sealed class WslcError(string kind, string message) : Exception(message)
     public const string PullFailed = "image_pull_failed";
     public const string StartFailed = "start_failed";
     public const string AiUnavailable = "ai_unavailable";
+
+    /// <summary>The installed wslc cannot do this at all (no pty, an unmappable signal). A
+    /// permanent capability gap, not a transient failure — hostd must not retry.</summary>
+    public const string Unsupported = "unsupported";
+
+    /// <summary>A session of that name is already running and this facade cannot re-adopt it
+    /// (the compat SDK's `Start()` answers ERROR_ALREADY_EXISTS, and its constructor is lazy, so
+    /// a second handle is not a second session). Distinct from <see cref="StartFailed"/> because
+    /// the remedy differs: the sandbox is UP, this broker just cannot reach it.</summary>
+    public const string SessionExists = "session_exists";
 }
 
 // DTOs — property names (after camel-casing) match the §3.3 wire keys exactly.