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

NucleicBroker/IWslc.cs

@@ -121,8 +121,16 @@ public sealed class WslcError(string kind, string message) : Exception(message)
     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>
+    /// <summary>
+    /// This broker build cannot serve the call as asked — no pty on the compat surface, a signal
+    /// outside wslc's six, an image whose `setpriv` cannot drop uid.
+    ///
+    /// "Not implemented yet", NOT "will never work": each of these has a route (the internal COM
+    /// pty, a wider signal map, a different image) that is simply **deprioritized until it can no
+    /// longer be avoided**. What the kind tells hostd is only that *retrying the same call against
+    /// the same broker will not help* — so surface it and move on rather than backing off and
+    /// trying again. Closing any of them is a change here, not a change in what wslc can do.
+    /// </summary>
     public const string Unsupported = "unsupported";
 
     /// <summary>