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

NucleicBroker.Tests/FakeWslc.cs

@@ -22,6 +22,10 @@ public sealed class FakeWslc : IWslc
     public long LastProcId;
     public Exception? NextError;
 
+    /// <summary>Set before a proc.exec to make that process emit during StartAsync — i.e. behave
+    /// like a command that finishes instantly.</summary>
+    public Action? NextProcessOnStart;
+
     public string? WslcVersion => "9.9-test";
 
     /// The fake is deliberately fully-capable: it stands in for a facade with BOTH wslc surfaces
@@ -157,7 +161,10 @@ public sealed class FakeWslc : IWslc
         if (ContainerStates.GetValueOrDefault(spec.Container) != "running")
             throw new WslcError(WslcError.NotRunning, $"container {spec.Container} isn't running");
         LastProcId = procId;
-        LastProcess = new FakeProcess();
+        // Mirror the real facade: create and attach, but do NOT run — BrokerService runs it after
+        // the procId response is on the wire.
+        LastProcess = new FakeProcess { OnStart = NextProcessOnStart };
+        NextProcessOnStart = null;
         return Task.FromResult<IWslcProcess>(LastProcess);
     }
 
@@ -167,6 +174,18 @@ public sealed class FakeWslc : IWslc
         public bool StdinClosed;
         public List<int> Signals = [];
         public (int Cols, int Rows)? LastResize;
+        public bool Started;
+
+        /// <summary>Lets a test stand in for a process that finishes DURING start — an `echo`,
+        /// which is what exposed the response-ordering bug on hardware.</summary>
+        public Action? OnStart;
+
+        public Task StartAsync(CancellationToken ct)
+        {
+            Started = true;
+            OnStart?.Invoke();
+            return Task.CompletedTask;
+        }
 
         public Task WriteStdinAsync(ReadOnlyMemory<byte> data, CancellationToken ct)
         {