chore: fit the loop-locals fix within the production gate

Three things the gate caught that the test suite could not.

The runtime size budget: writing `data-wrn-loop-locals` on client-rendered
loop items pushed reactive-runtime.ts to 51,603 against a 51,400 budget that
had only 125 bytes of headroom. Trimmed the encoder to the
btoa/encodeURIComponent idiom, recovering 65 bytes and leaving the smallest
form that still handles non-ASCII, then raised the budget to 51,600 with the
reason recorded in the file's own convention -- the remaining 263 bytes buy a
correctness fix, not a feature.

The VS Code extension bundles its own copy of the compiler, so the syntax and
compiler fixes made it stale. Rebuilt.

And a bug in the new test: `\{` inside a template literal is an unnecessary
escape, so the "brace inside a regex" case was testing an unescaped brace.
`\{` tests the case it was written for.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/csr/src/reactive-runtime.ts

@@ -999,20 +999,11 @@ export const REACTIVE_RUNTIME = String.raw`
         var json = JSON.stringify(locals);
         if (json === undefined) return;
 
-        var bytes = new TextEncoder().encode(json);
-        var binary = "";
-
-        for (var index = 0; index < bytes.length; index++) {
-          binary += String.fromCharCode(bytes[index]);
-        }
-
-        node.setAttribute("data-wrn-loop-locals", window.btoa(binary));
+        node.setAttribute(
+          "data-wrn-loop-locals",
+          window.btoa(unescape(encodeURIComponent(json))),
+        );
       } catch (error) {
-        /*
-         * A value that will not serialise (a cycle, a DOM node) must not take
-         * the whole loop down -- the item still renders, and a handler naming
-         * that local fails on its own terms rather than silently.
-         */
         console.error("[wrnexus] failed to encode loop locals", error);
       }
     }