mohdel v0.104.2

Fixed

• cancelledDone now threads cacheWriteInputTokens /
  cacheReadInputTokens captured pre-cancellation. Previously a
  mid-stream abort produced a terminal done.result with cache
  fields dropped, under-counting cost on cancelled calls.
• [mohdel:answer] done debug log surfaces cacheW / cacheR
  when present, so per-call cache activity is visible without
  attaching to the OTel span.

Changed

• AnswerResult / Status / Timestamps derive Default.
  Test fixtures and stub-construction sites can now use
  ..Default::default() instead of listing every field. New optional
  fields no longer break literal-construction sites at compile time.
• Wire-field-add checklist documented in CONTRIBUTING.md.
  Eight sites a new field touches (JS type, adapter, pricing, Rust
  struct, conformance fixture, JS allowlist, log summarizer,
  CHANGELOG framing) — captured so future field additions land in one
  PR rather than three.