Adds a third comparison arm to measure_signposting_rate(): Task 19c's
first per-code pass (git ref da72bf3, self-coverage allowed) alongside
the existing coarse (b0df1ec) and live corrected per-code arms, pulled
verbatim via the same git-show mechanism (renamed
.measure_load_coarse_impl -> .measure_load_git_impl since it now loads
more than the coarse arm).
Reports both the original delta (self-coverage-allowed rate minus
coarse) and the corrected delta (live per-code rate minus coarse), plus
the self-coverage share of the original delta (queries that fired ONLY
because a component's own aggregate row satisfied its own coverage
check). Verifies percode-fired is always a subset of selfcov-fired
(stopifnot) -- the corrected arm is a strict narrowing of the buggy one,
so the decomposition is exact rather than approximate.
jared
9244e08085