🤖 feat: add millions unit to token formatting (#1211)

Update `formatTokens` to display `M` suffix for values >= 1M tokens.

Previously showed `58507.9k` for ~58M tokens, now shows `58.5M`.

---
_Generated with `mux` • Model: `anthropic:claude-opus-4-5` • Thinking:
`high`_

Author: ethanndickson

src/common/utils/tokens/tokenMeterUtils.test.ts

@@ -0,0 +1,24 @@
+import { describe, expect, test } from "bun:test";
+import { formatTokens } from "./tokenMeterUtils";
+
+describe("formatTokens", () => {
+  test("formats small numbers as-is with locale formatting", () => {
+    expect(formatTokens(0)).toBe("0");
+    expect(formatTokens(500)).toBe("500");
+    expect(formatTokens(999)).toBe("999");
+  });
+
+  test("formats thousands with k suffix", () => {
+    expect(formatTokens(1000)).toBe("1.0k");
+    expect(formatTokens(1500)).toBe("1.5k");
+    expect(formatTokens(58507)).toBe("58.5k");
+    expect(formatTokens(999_999)).toBe("1000.0k");
+  });
+
+  test("formats millions with M suffix", () => {
+    expect(formatTokens(1_000_000)).toBe("1.0M");
+    expect(formatTokens(1_500_000)).toBe("1.5M");
+    expect(formatTokens(58_507_900)).toBe("58.5M");
+    expect(formatTokens(4_133_000)).toBe("4.1M");
+  });
+});

src/common/utils/tokens/tokenMeterUtils.ts

@@ -100,7 +100,13 @@ export function calculateTokenMeterData(
 }
 
 export function formatTokens(tokens: number): string {
-  return tokens >= 1000 ? `${(tokens / 1000).toFixed(1)}k` : tokens.toLocaleString();
+  if (tokens >= 1_000_000) {
+    return `${(tokens / 1_000_000).toFixed(1)}M`;
+  }
+  if (tokens >= 1_000) {
+    return `${(tokens / 1_000).toFixed(1)}k`;
+  }
+  return tokens.toLocaleString();
 }
 
 export function getSegmentLabel(type: TokenSegment["type"]): string {