routie dev init since i didn't adhere to any proper guidance up until now

frontend/node_modules/eslint-plugin-perfectionist/dist/utils/unreachable-case-error.d.ts

@@ -0,0 +1,43 @@
+/**
+ * Error class for exhaustive type checking in switch statements and
+ * conditionals.
+ *
+ * Ensures at compile-time that all possible cases of a union type are handled.
+ * When TypeScript's type system proves all cases are covered, the variable in
+ * the default case has type `never`, making this error theoretically
+ * unreachable in correctly typed code.
+ *
+ * This pattern is crucial for maintaining type safety when adding new options
+ * to existing types - TypeScript will error if a new case isn't handled.
+ *
+ * @example
+ *
+ * ```ts
+ * // Exhaustive handling of sorting types
+ * function getSortingAlgorithm(
+ *   type: 'alphabetical' | 'natural' | 'custom',
+ * ) {
+ *   switch (type) {
+ *     case 'alphabetical':
+ *       return alphabeticalSort
+ *     case 'natural':
+ *       return naturalSort
+ *     case 'custom':
+ *       return customSort
+ *     default:
+ *       throw new UnreachableCaseError(type)
+ *     // TypeScript ensures 'type' is 'never' here
+ *   }
+ * }
+ * ```
+ */
+export declare class UnreachableCaseError extends Error {
+  /**
+   * Creates an error indicating that an supposedly unreachable case was
+   * reached.
+   *
+   * @param value - The value that should have type `never` if all cases are
+   *   handled. In practice, this will contain the unhandled case value.
+   */
+  constructor(value: never)
+}