COMMON_TERM_FRACTION = 0.05 is a magic number unless something prints the curve it
came from. bench/term_sweep.py asks the frozen suite as its holders would, once per
candidate bound, and writes recall and latency into the same row of
bench/reports/TERMS.md.
rare_terms now resolves its bound when the call runs instead of when the function was
defined, which is the only way a harness can move it. The default value is unchanged,
so the reports stamped at the parent commit still describe this code.
