Liminalia partnerships and births

liminalia

ccfb638 — relationships have consequences.

The relationship graph already promoted pairs to Partner at 0.8 affinity, but partnerships were cosmetic. Nothing followed from them, and the population was a fixed set of 50 that could only drain through old age.

cohabitation

PartnershipService formalises a Partner relationship between two adults who do not already share a household: one partner's household is reused, the other leaves their old household and joins it, and the shared home anchors the household.

births

Cohabiting partners of child-bearing age (18–45) have a chance each simulated year of a birth — a new citizen, age 0, birthday anchored a year out, homed and householded with the parents. The child then flows through the same life course as anyone else: school at 7, work at 18, retirement at 65, death at 90.

The birth chance is per-year and prorated by the step's fraction of a year using 1 − (1 − p)^years — the same correct-at-any-step-size form as the fire ignition fix. The naive rate × years form would have guaranteed births on long fast-forwards.

Five new tests, 320 total.