Match the `LLMResponse.text` / `reasoning` / `toolCalls` getter pattern
in the same file — `usage.totalInputTokens` reads naturally and lives
where the Usage data does. Both sums are monotonic under the additive
contract, so callers no longer need to remember which fields are
non-overlapping.
Test fixtures that previously asserted with `usage: { ... }` plain
literals are now wrapped with `new Usage({...})` to match the runtime
shape the mappers actually produce (an instance, not a struct).
Kit Langton
f5d199db62