fix: restore Anthropic token accounting

src/agents/usage.test.ts

@@ -0,0 +1,50 @@
+import { describe, expect, it } from "vitest";
+
+import { hasNonzeroUsage, normalizeUsage } from "./usage.js";
+
+describe("normalizeUsage", () => {
+  it("normalizes Anthropic-style snake_case usage", () => {
+    const usage = normalizeUsage({
+      input_tokens: 1200,
+      output_tokens: 340,
+      cache_creation_input_tokens: 200,
+      cache_read_input_tokens: 50,
+      total_tokens: 1790,
+    });
+    expect(usage).toEqual({
+      input: 1200,
+      output: 340,
+      cacheRead: 50,
+      cacheWrite: 200,
+      total: 1790,
+    });
+  });
+
+  it("normalizes OpenAI-style prompt/completion usage", () => {
+    const usage = normalizeUsage({
+      prompt_tokens: 987,
+      completion_tokens: 123,
+      total_tokens: 1110,
+    });
+    expect(usage).toEqual({
+      input: 987,
+      output: 123,
+      cacheRead: undefined,
+      cacheWrite: undefined,
+      total: 1110,
+    });
+  });
+
+  it("returns undefined for empty usage objects", () => {
+    expect(normalizeUsage({})).toBeUndefined();
+  });
+
+  it("guards against empty/zero usage overwrites", () => {
+    expect(hasNonzeroUsage(undefined)).toBe(false);
+    expect(hasNonzeroUsage(null)).toBe(false);
+    expect(hasNonzeroUsage({})).toBe(false);
+    expect(hasNonzeroUsage({ input: 0, output: 0 })).toBe(false);
+    expect(hasNonzeroUsage({ input: 1 })).toBe(true);
+    expect(hasNonzeroUsage({ total: 1 })).toBe(true);
+  });
+});