fix(status): account cached prompt tokens

src/agents/usage.ts

@@ -0,0 +1,69 @@
+export type UsageLike = {
+  input?: number;
+  output?: number;
+  cacheRead?: number;
+  cacheWrite?: number;
+  total?: number;
+  // Some agents/logs emit alternate naming.
+  totalTokens?: number;
+  total_tokens?: number;
+  cache_read?: number;
+  cache_write?: number;
+};
+
+const asFiniteNumber = (value: unknown): number | undefined => {
+  if (typeof value !== "number") return undefined;
+  if (!Number.isFinite(value)) return undefined;
+  return value;
+};
+
+export function normalizeUsage(raw?: UsageLike | null):
+  | {
+      input?: number;
+      output?: number;
+      cacheRead?: number;
+      cacheWrite?: number;
+      total?: number;
+    }
+  | undefined {
+  if (!raw) return undefined;
+
+  const input = asFiniteNumber(raw.input);
+  const output = asFiniteNumber(raw.output);
+  const cacheRead = asFiniteNumber(raw.cacheRead ?? raw.cache_read);
+  const cacheWrite = asFiniteNumber(raw.cacheWrite ?? raw.cache_write);
+  const total = asFiniteNumber(
+    raw.total ?? raw.totalTokens ?? raw.total_tokens,
+  );
+
+  if (
+    input === undefined &&
+    output === undefined &&
+    cacheRead === undefined &&
+    cacheWrite === undefined &&
+    total === undefined
+  ) {
+    return undefined;
+  }
+
+  return {
+    input,
+    output,
+    cacheRead,
+    cacheWrite,
+    total,
+  };
+}
+
+export function derivePromptTokens(usage?: {
+  input?: number;
+  cacheRead?: number;
+  cacheWrite?: number;
+}): number | undefined {
+  if (!usage) return undefined;
+  const input = usage.input ?? 0;
+  const cacheRead = usage.cacheRead ?? 0;
+  const cacheWrite = usage.cacheWrite ?? 0;
+  const sum = input + cacheRead + cacheWrite;
+  return sum > 0 ? sum : undefined;
+}