Token formatter PR15599; base34c5a6d446; head886bcffc96;3 token behavior tests versus9 original cases;12 fullsuite versus18.

BASE implementation with takeover tests:
note: You are running `vp test` as a Vite+ built-in command. If you meant to run the test npm script, use `vpr test` instead.

 RUN  v5.0.1 /home/ubuntu/wt/usage-billing-01

 ❯ packages/shared/src/usageFormat.test.ts (12 tests | 2 failed) 23ms
   ❯ formatTokens (3)
     × promotes units when three-significant-figure rounding reaches the next unit 7ms
     × preserves negative signs and NaN 1ms

⎯⎯⎯⎯⎯⎯⎯ Failed Tests 2 ⎯⎯⎯⎯⎯⎯⎯

 FAIL  packages/shared/src/usageFormat.test.ts > formatTokens > promotes units when three-significant-figure rounding reaches the next unit
AssertionError: expected '1,000' to be '1K' // Object.is equality

Expected: "1K"
Received: "1,000"

 ❯ packages/shared/src/usageFormat.test.ts:16:33
     14| describe("formatTokens", () => {
     15|   it("promotes units when three-significant-figure rounding reaches th…
     16|     expect(formatTokens(999.6)).toBe("1K");
       |                                 ^
     17|     expect(formatTokens(999_600)).toBe("1M");
     18|     expect(formatTokens(999_600_000)).toBe("1B");

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 FAIL  packages/shared/src/usageFormat.test.ts > formatTokens > preserves negative signs and NaN
AssertionError: expected '-1000K' to be '-1M' // Object.is equality

Expected: "-1M"
Received: "-1000K"

 ❯ packages/shared/src/usageFormat.test.ts:31:36
     29|
     30|   it("preserves negative signs and NaN", () => {
     31|     expect(formatTokens(-999_600)).toBe("-1M");
       |                                    ^
     32|     expect(formatTokens(Number.NaN)).toBe("NaN");
     33|   });

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 Test Files  1 failed (1)
      Tests  2 failed | 10 passed (12)
   Start at  16:10:14
   Duration  1.91s (transform 61%, import 33%, setup 5%, tests 1%)


HEAD:
note: You are running `vp test` as a Vite+ built-in command. If you meant to run the test npm script, use `vpr test` instead.

 RUN  v5.0.1 /home/ubuntu/wt/usage-billing-01


 Test Files  1 passed (1)
      Tests  12 passed (12)
   Start at  16:10:18
   Duration  1.87s (transform 60%, import 33%, setup 5%, tests 1%)


Shared typecheck, targeted lint/fmt/diff passed; Opus additionally ran formatter+work-log presentation suites115pass.
Browser: actual Usage page with synthetic999600 input tokens,1280x800 light theme and identical fixture font; base1000K→head1M. No real usage data/provider turns.
Not exercised: native macOS/Windows/Electron/iOS/Android.