feat: add local auth billing and usage management

lib/seedance/client.ts

@@ -26,9 +26,14 @@ export type SeedanceQueryResult = {
   status: "queued" | "running" | "succeeded" | "failed" | "cancelled";
   resultUrl?: string;
   errorMessage?: string;
+  usage?: SeedanceUsage;
   raw: Record<string, unknown>;
 };
 
+export type SeedanceUsage = {
+  completionTokens: number;
+};
+
 export function getSeedanceConfig() {
   const model = process.env.SEEDANCE_MODEL || "doubao-seedance-2-0-260128";
   return {
@@ -107,10 +112,21 @@ export async function querySeedanceTask(providerTaskId: string): Promise<Seedanc
       json.data?.url ||
       json.data?.output,
     errorMessage: json.error?.message || json.data?.error?.message,
+    usage: extractSeedanceUsage(json),
     raw: json as Record<string, unknown>
   };
 }
 
+export function extractSeedanceUsage(value: unknown): SeedanceUsage | undefined {
+  const root = recordValue(value);
+  const data = recordValue(root?.data);
+  const usage = recordValue(root?.usage) || recordValue(data?.usage);
+  if (!usage) return undefined;
+  const completionTokens = Number(usage.completion_tokens ?? usage.completionTokens);
+  if (!Number.isFinite(completionTokens) || completionTokens <= 0) return undefined;
+  return { completionTokens: Math.floor(completionTokens) };
+}
+
 function normalizeSeedanceStatus(status: unknown): SeedanceQueryResult["status"] {
   const value = String(status || "").toLowerCase();
   if (["succeeded", "success", "completed"].includes(value)) return "succeeded";
@@ -119,3 +135,9 @@ function normalizeSeedanceStatus(status: unknown): SeedanceQueryResult["status"]
   if (["running", "processing", "generating"].includes(value)) return "running";
   return "queued";
 }
+
+function recordValue(value: unknown): Record<string, unknown> | undefined {
+  return typeof value === "object" && value !== null && !Array.isArray(value)
+    ? value as Record<string, unknown>
+    : undefined;
+}