feat(client): step token figures up to billions in fmt

Values at 1e9 and above rendered as four-digit M figures (1055.9M);
fmt now steps to a one-decimal B suffix, same style as k and M.

src/client/format.ts

@@ -1,9 +1,10 @@
-/** `fmt`: the k/M suffix style shared by bars/details/stats; `fmtTime`: local HH:MM:SS. */
+/** `fmt`: the k/M/B suffix style shared by bars/details/stats; `fmtTime`: local HH:MM:SS. */
 
 export function fmt(n: number | null | undefined): string {
   if (n === undefined || n === null || isNaN(n)) return '—'
   const sign = n < 0 ? '-' : ''
   const a = Math.abs(n)
+  if (a >= 1e9) return sign + (a / 1e9).toFixed(1) + 'B'
   if (a >= 1e6) return sign + (a / 1e6).toFixed(1) + 'M'
   if (a >= 1000) return sign + (a / 1000).toFixed(1) + 'k'
   return sign + String(Math.round(a))

tests/client/format.spec.ts

@@ -1,4 +1,4 @@
-// Display formatting (src/client/format.ts): the k/M suffix style, byte
+// Display formatting (src/client/format.ts): the k/M/B suffix style, byte
 // sizes, the cache-hit truncation, locale-safe time, locale-unit durations,
 // and leading slice shares.
 
@@ -18,16 +18,19 @@ describe('fmt', () => {
     assert.equal(fmt(999.4), '999')
   })
 
-  test('thousands and millions take suffixes with one decimal', () => {
+  test('thousands, millions, and billions take suffixes with one decimal', () => {
     assert.equal(fmt(1000), '1.0k')
     assert.equal(fmt(1534), '1.5k')
     assert.equal(fmt(1_000_000), '1.0M')
     assert.equal(fmt(128_000), '128.0k')
+    assert.equal(fmt(1_000_000_000), '1.0B')
+    assert.equal(fmt(1_055_900_000), '1.1B')
   })
 
   test('negatives keep their sign', () => {
     assert.equal(fmt(-1500), '-1.5k')
     assert.equal(fmt(-12), '-12')
+    assert.equal(fmt(-2_000_000_000), '-2.0B')
   })
 })