0.11.2: --max-usd holds when calls run side by side

• --max-usd holds when calls run side by side. A call that returned gave its estimate back, wrote its answer to
  the cache and only then counted what it cost, so a call asked in that gap (asked runs four at once) saw room that
  was already spent and could take the run past the cap even when every call cost no more than its estimate. The
  estimate is now replaced by the cost in one step, before the cache is written, and a test holds a call in that
  gap. A skills list's reviewer found it.
• The cap is described as what it is, in the help, the skill, the MCP server's tools and the READMEs, which said
  "never more than" and "at most": a call is made only while its estimated price still fits. The estimates are
  prices seen before, at or above what the calls cost then, not prices the providers guarantee, so a call billed
  above its estimate (a longer answer from a model, a price raised since) can take a run past the cap by the
  difference.