- subtractTokens JSDoc said the raw payload lives on Usage.native, but
that field was renamed to providerMetadata earlier in this PR.
- totalTokens JSDoc still described the abandoned "additive" first-pass
contract where inputTokens/outputTokens were non-cached / visible only.
We landed on inclusive totals; the fallback already covers cache and
reasoning.
- Removed a duplicate inline comment in Gemini's mapUsage — the
function-level comment already explains the visible/reasoning sum and
the undefined-when-incomplete rule.
c20d070b9a