POLISH-1: gridify emits canonical '='; localize litter InvalidParentGender 400 (ApiError body) + de strings

gerbil-manager-web/src/api/client.ts

@@ -13,15 +13,27 @@ export class ApiError extends Error {
   readonly status: number | null
   /** The request path that failed (for diagnostics/logging). */
   readonly path?: string
+  /** Parsed error response body, if any (e.g. { code, ... } for 400s). */
+  readonly body?: unknown
 
-  constructor(message: string, status: number | null, path?: string) {
+  constructor(message: string, status: number | null, path?: string, body?: unknown) {
     super(message)
     this.name = 'ApiError'
     this.status = status
     this.path = path
+    this.body = body
   }
 }
 
+/** Read a `code` field off a parsed ApiError body, if present. */
+export function errorCode(err: unknown): string | null {
+  if (err instanceof ApiError && err.body && typeof err.body === 'object' && 'code' in err.body) {
+    const code = (err.body as { code: unknown }).code
+    return typeof code === 'string' ? code : null
+  }
+  return null
+}
+
 function errorMessageFor(status: number): string {
   if (status === 404) return de.api.errors.notFound
   if (status >= 500) return de.api.errors.server
@@ -40,7 +52,14 @@ async function request<T>(path: string, init?: RequestInit): Promise<T> {
   }
 
   if (!response.ok) {
-    throw new ApiError(errorMessageFor(response.status), response.status, path)
+    // Best-effort parse of a JSON error body (e.g. { code: "InvalidParentGender" }).
+    let body: unknown
+    try {
+      body = await response.clone().json()
+    } catch {
+      body = undefined
+    }
+    throw new ApiError(errorMessageFor(response.status), response.status, path, body)
   }
 
   if (response.status === 204) {