fix(core-eslint): fail loudly on unparseable manifest in wiring gate

usecase-must-be-wired returned {} when the manifest parsed to null,
silently disabling the error-level gate when the manifest existed but
could not be read. It now reports unparseableManifest on Program in
that case; a genuinely missing manifest stays a no-op (that is
feature-must-have-manifest's job).

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

packages/core-eslint/rules/usecase-must-be-wired.js

@@ -1,3 +1,4 @@
+import fs from "node:fs";
 import path from "node:path";
 import { parseManifestUseCases } from "./_manifest-ast.js";
 import {
@@ -39,6 +40,8 @@ export default {
     messages: {
       missing:
         'Use case "{{useCase}}" is declared in {{feature}}.manifest.ts but not wired through wireUseCase({ name: "{{useCase}}", ... }) in this binder. Add the wireUseCase call or remove the manifest entry.',
+      unparseableManifest:
+        "feature.manifest.ts for {{feature}} exists but could not be parsed by the conformance rules; the wiring gate cannot run. Fix the manifest shape (defineFeature({...} as const)).",
     },
   },
   create(context) {
@@ -49,8 +52,23 @@ export default {
 
     const featureRoot = featureRootForFile(filename, repoRoot);
     if (!featureRoot) return {};
-    const manifest = parseManifestUseCases(manifestPathForFeature(featureRoot));
-    if (!manifest) return {};
+    const manifestPath = manifestPathForFeature(featureRoot);
+    const manifest = parseManifestUseCases(manifestPath);
+    if (!manifest) {
+      // An unparseable manifest must FAIL the gate, not silently disable it.
+      if (fs.existsSync(manifestPath)) {
+        return {
+          Program(node) {
+            context.report({
+              node,
+              messageId: "unparseableManifest",
+              data: { feature: path.basename(featureRoot) },
+            });
+          },
+        };
+      }
+      return {};
+    }
     const declaredNames = Object.keys(manifest);
     if (declaredNames.length === 0) return {};
     const featureName = path.basename(featureRoot);