Fogbugz is (was?) writing a language for internal use only, so it's a better fit there.
jq stores all numbers as doubles, which means it can't handle 64 bit ints (or larger integer numeric types).
It's otherwise a great tool and I wouldn't point out a negative such as this, but you did explicitly mention that you know JSON won't be fed to a bad parser.
This specification allows implementations to set limits on the range and precision of numbers accepted. Since software that implements IEEE 754-2008 binary64 (double precision) numbers [IEEE754] is generally available and widely used, good interoperability can be achieved by implementations that expect no more precision or range than these provide, in the sense that implementations will approximate JSON numbers within the expected precision. A JSON number such as 1E400 or 3.141592653589793238462643383279 may indicate potential interoperability problems, since it suggests that the software that created it expects receiving software to have greater capabilities for numeric magnitude and precision than is widely available.JSON = JavaScript Object Notation.
Javascript do NOT have integers. It's representing all numbers as double, which causes all kind of weird bugs and rounding errors.