Keep the private-brand diagnostics on shapes that still refuse

Function-local classes whose private names are used only on `this` now
compile, so the two diagnostics fixtures test a brand check on another
object instead.

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

tests/diagnostics/local-class-boundaries.ts

@@ -1,4 +1,4 @@
-function privateBrand() { return class { #value = 1; read(): number { return this.#value; } }; }
+function privateBrand() { return class { #value = 1; has(other: object): boolean { return #value in other; } }; }
 function selfName() { return class Local { copy() { return new Local(); } }; }
 class Base {}
 function derived() { return class extends Base {}; }

tests/diagnostics/local-class-type-query-brand.ts

@@ -1,11 +1,15 @@
 // The same speculative element-type query, reaching a function-local class
-// with a private brand through the function's returned array.
+// with a private brand through the function's returned array. The brand is
+// tested on another object, so the evaluations' private names must differ.
 function make() {
   class Box {
     #v = 1;
     read(): number {
       return this.#v;
     }
+    same(other: object): boolean {
+      return #v in other;
+    }
   }
   return [new Box()];
 }

tests/harness/__snapshots__/local-class-boundaries.ts.txt

@@ -1,12 +1,12 @@
 local-class-boundaries.ts:1:34 - error SC1090: function-local classes with private brands are not supported yet
 
-  1 | function privateBrand() { return class { #value = 1; read(): number { return this.#value; } }; }
-    |                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+  1 | function privateBrand() { return class { #value = 1; has(other: object): boolean { return #value in other; } }; }
+    |                                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   2 | function selfName() { return class Local { copy() { return new Local(); } }; }
 
 local-class-boundaries.ts:2:64 - error SC1090: named self references inside function-local classes are not supported yet
 
-  1 | function privateBrand() { return class { #value = 1; read(): number { return this.#value; } }; }
+  1 | function privateBrand() { return class { #value = 1; has(other: object): boolean { return #value in other; } }; }
   2 | function selfName() { return class Local { copy() { return new Local(); } }; }
     |                                                                ^~~~~
   3 | class Base {}

tests/harness/__snapshots__/local-class-type-query-brand.ts.txt

@@ -1,6 +1,6 @@
-local-class-type-query-brand.ts:4:3 - error SC1090: function-local classes with private brands are not supported yet
+local-class-type-query-brand.ts:5:3 - error SC1090: function-local classes with private brands are not supported yet
 
-  3 | function make() {
-  4 |   class Box {
+  4 | function make() {
+  5 |   class Box {
     |   ^~~~~~~~~~~
-  5 |     #v = 1;
+  6 |     #v = 1;