fix(executor): restore logging for invalid JSON in parseRoutes

parseJSON(input, []) returns [] on parse failure, making the
subsequent !Array.isArray check unreachable for the invalid-JSON case.
Use null as the fallback to distinguish parse failure from valid-but-
not-array, and log both cases separately.

Author: rpatricksmith

apps/sim/executor/handlers/router/router-handler.ts

@@ -375,11 +375,15 @@ export class RouterBlockHandler implements BlockHandler {
     if (Array.isArray(input)) {
       return input
     }
-    const parsed = parseJSON(input, [])
-    if (!Array.isArray(parsed)) {
+    const parsed = parseJSON(input, null)
+    if (parsed === null) {
       logger.error('Failed to parse routes:', { input })
       return []
     }
+    if (!Array.isArray(parsed)) {
+      logger.error('Routes parsed but is not an array:', { input, parsed })
+      return []
+    }
     return parsed
   }