quality_uncrinkliness evaluates a gaussian at x = 1/crink, so its exponent
grows like 1/crink^2 and underflows a double to exactly zero below crink ~
1/15. Measured over the twelve 500k cold-start runs (39.12): 430 leaves carry
a minimum-exposure requirement, 112 fail it, and those 112 span quality
1e-300..1e-1 while contributing 0.034% of total value on 23% of the floor
area. Every value in that range is numerically zero beside a passing leaf's
~1, so the search cannot rank two layouts that differ only in how exposed
their under-lit rooms are.
This is wider than the bead's diagnosis (a flat 0.0 for zero-exposure leaves)
and it explains why 38.1's `floor` mode measured as a no-op: max(q, 0.01) maps
110 of the 112 onto one constant, replacing a flat zero with a flat 0.01.
crinkliness_tail="ramp" (default OFF, "gaussian" is stock) replaces the tail --
only the tail, only below FAIL_THRESHOLD, only on the compact side -- with a
straight line in crinkliness meeting the gaussian exactly at the crossing.
_crink_at_fail_threshold inverts the gaussian there using the same truncated
_E the factor is evaluated with.
Deliberately conservative: nothing at or above FAIL_THRESHOLD moves, so no
calibration changes and no leaf crosses the threshold. The fail set is
byte-identical on all 21 committed corpus artefacts, the four init.dom seeds
included -- asserted in tests/test_fitness_crinkliness_tail.py, not assumed.
That invariance is also what makes it legal to score both arms of the A/B
under stock (the 38.9 trap's one exemption). A fully buried leaf still scores
exactly 0; this restores an ordering within the failing region, it does not
forgive it. Composing with 38.1's superseded modes is refused, since both
rewrite the same tail.
Score effect on the baseline artefacts: +0.3%..+2.8% on harbor and maple,
exactly +0.000% on health-centre, programme-house, and every init.dom -- a
programme with no partially-exposed failing rooms has nothing to grade, and
neither does any starting layout. The ramp is a mid-search signal by
construction, so experiments/ab_9gj_ramp.py defaults to seeding each run from
a 500k plateau artefact rather than cold.
The module-level math import replaces a now-redundant local one.
DESIGN.md 39.13 and the A/B verdict follow in a separate commit.
Refs homemaker-py-9gj.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MJ84Feep79Hhm3E4zZJmnB
