Builds path (b) from §26 -- a leaf permanently serving two DIFFERENT
compatible programme codes at once, extending leaf-sharing's same-code
multiplicity mechanism to different-but-compatible codes. Architect-declared
`co_locate` pairs (validated against interchangeable()'s S1-S4 bounds, no
transitive closure so the b3v chain problem can't recur), threaded through
graph.py's checks via a new leaf_codes() resolver and fitness.py's quality
terms (additive size, stricter-of-both width/proportion). Construction-time
only, gated behind `multi_use` (default OFF, bit-identical when off).
End-to-end A/B (20k evals x 3 seeds x 2 programmes) came back net negative:
harbor-house -4.0% but health-centre +24.5% worse (3/3 seeds), because
fusing different codes' shape targets via stricter-of-both can impose a
tighter joint constraint than either code needed alone, which the tightly-
packed health-centre programme can't absorb. Written up as DESIGN.md §33;
multi_use stays default OFF, no default-flip recommended.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01R8agJBT2ZpmF3ErW7wi2wY
A small primary-care health centre: 19 distinct, individually-sized room
codes at n=20 room instances (only one deliberate duplication: two public
WCs), filling the gap between programme-house's duplicated-count sweep
sizes and harbor-house's out-of-range 37 real-diversity instances. Widths
are deliberately tiered (>1.3x gaps at three boundaries) so the auto-derived
interchange relation resolves to three bounded utility/office/clinical
classes instead of one whole-building chain, which a first pass produced.
experiments/run_9yx_sweep.sh repeats xyu's ruin_recreate ON/OFF protocol
(budget 3000, 4 workers, N=15 seeds) against this programme.
