Fix #746: nested namespace shadowing same-named top-level namespace throws in interpreter

Execution/Interpreter.Namespaces.cs

@@ -16,8 +16,11 @@ private ExecutionResult ExecuteNamespace(Stmt.Namespace ns)
     {
         string name = ns.Name.Lexeme;
 
-        // Get or create namespace object
-        SharpTSNamespace? existingNs = _environment.GetNamespace(name);
+        // Get or create namespace object — check ONLY the current scope, not up the chain.
+        // GetNamespace walks up and would find a same-named outer namespace (e.g. top-level A
+        // when declaring O.A), incorrectly merging the nested namespace into the outer one and
+        // leaving the current scope without an "A" binding (#746).
+        SharpTSNamespace? existingNs = _environment.GetLocalNamespace(name);
         SharpTSNamespace nsObj;
 
         if (existingNs != null)

Runtime/RuntimeEnvironment.cs

@@ -154,6 +154,17 @@ public void DefineNamespace(string name, SharpTSNamespace ns)
         return Enclosing?.GetNamespace(name);
     }
 
+    /// <summary>
+    /// Gets a namespace by name from THIS scope only (no chain traversal).
+    /// Use when deciding whether to merge vs. create a new namespace declaration —
+    /// avoids treating a same-named namespace in an enclosing scope as a merge target (#746).
+    /// </summary>
+    public SharpTSNamespace? GetLocalNamespace(string name)
+    {
+        _namespaces.TryGetValue(name, out var ns);
+        return ns;
+    }
+
     /// <summary>
     /// Defines a variable with a boxed value (legacy compatibility).
     /// Wraps the value in RuntimeValue.FromBoxed automatically.

SharpTS.Tests/SharedTests/NamespaceTests.cs

@@ -796,5 +796,25 @@ export namespace I {
         Assert.Equal("2\n", TestHarness.Run(code, mode));
     }
 
+    [Theory]
+    [MemberData(nameof(ExecutionModes.All), MemberType = typeof(ExecutionModes))]
+    public void NestedNamespace_ShadowsSameNamedTopLevelNamespace(ExecutionMode mode)
+    {
+        // Nested O.A shadows the top-level A for bare references from sibling O.B.
+        // The interpreter previously merged O.A's members into the global A and left
+        // namespaceEnvO without an "A" binding, so the pre-resolved distance-2 lookup
+        // returned Undefined → "Only instances and objects have properties" (#746).
+        var code = @"
+            namespace A { export function g() { return 100; } }
+            namespace O {
+              export namespace A { export function g() { return 5; } }
+              export namespace B { export function f() { return A.g(); } }
+            }
+            console.log(O.B.f());
+            console.log(A.g());
+        ";
+        Assert.Equal("5\n100\n", TestHarness.Run(code, mode));
+    }
+
     #endregion
 }