fix: price 1-hour TTL cache writes at 2x input (fixes #44) - #45

Fixes #44.

What

calculateCost charged every cache-creation token at cacheCreatePerMillion (3.75, i.e. 1.25x input). That rate is the 5-minute cache-write tier. Claude Code writes most of its cache with a 1-hour TTL, which Anthropic bills at 2x input, so reported cost came out low.

The API already returns the split alongside the aggregate:

"usage": {
  "cache_creation_input_tokens": 3904,
  "cache_creation": {
    "ephemeral_5m_input_tokens": 0,
    "ephemeral_1h_input_tokens": 3904
  }
}

calculateCost now reads it and prices each portion at its own rate.

Scale

On a 425-file ~/.claude/projects corpus, 168,726,465 of 216,447,883 cache-creation tokens (78%) were 1-hour TTL. Billing that share at 1.25x instead of 2x understates the cache-write component by 37.5%.

Notes on the implementation

The 1-hour rate is derived as inputPerMillion * 2 rather than added as a fifth setting, so it follows a user's inputPerMillion override and there's nothing new to configure. Happy to switch it to a cacheCreate1hPerMillion config key instead if you'd prefer it explicit — that's a small change and I'll follow your call.

Two edge cases from the issue are handled and covered by tests:

• entries with no cache_creation object keep the whole bucket on the 5-minute rate, so older logs behave exactly as before
• the 1-hour count is clamped to the aggregate, so a malformed record can't inflate the total (I saw 22 such records in ~41k)

The breakdown is also threaded through the three places that rebuild TokenUsage by hand — prediction.ts, projectCost.ts and heatmap.ts. Without that, prediction, project cost and the heatmap would have kept charging the 5-minute rate while the status bar showed the corrected figure. projectCost.ts needed its rawUsage cast widened from Record<string, number> to Partial<TokenUsage> to carry the nested object.

Checks

npm run lint and npm test both clean — 69 passing, including 5 new cases: the all-1h rate, a mixed bucket, the no-breakdown fallback, the clamp, and custom pricing.

docs/DATA.md and CHANGELOG.md are updated to match.