Add missing test files

Correction 1: 38.8's A/B scores every arm under stock urb, which is only
sound if stock is ground truth -- and stock is what this section shows is
miscalibrated. Scoring the repair under the objective it repairs penalises
it for repairing. That result is not evidence against usage_daylight.

The measurement that matters needs no search: are the emitted failures
true? audit_crinkliness_truth.py classifies every stock crinkliness fail by
the leaf's declared usage. 164 of 271 (61%) are reported against spaces
that want no daylight -- stores, WCs, plant, corridors, covered courtyards
-- and it holds on evolved artefacts (maple generated.dom: 64%), not just
constructed seeds. Under value *= 0.5 ** len(failures) each one halves the
fitness of a design that did nothing wrong.

Correction 2: usage: is the wrong key, and usage_daylight as written
mis-keys it. 39.7 established usage: as an ACCESS-requirement class.
"Needs no special access" and "needs no window" are different questions,
and the corpus separates them: usage: none is Waiting Room, Reception,
Reception Office, Entrance Foyer -- a waiting room plainly wants daylight
and DAYLIGHT_USAGES exempts it. The usage: bedroom half is right, but by
luck of where the access axis happened to fall.

The audit is robust to that error (61% -> 57% if none is reclassified), so
the finding stands; the design does not. Daylight needs its own declared
per-space axis, decided by the programme author as usage: was.

usage_daylight stays default off and is not the shipping fix. The
compact-side clip is the right shape for the factor, so the mechanism is
retained pending a daylight: attribute to key it on.

Higher-power A/B stopped: it was chasing a score against a flawed objective
with a mis-keyed fix.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MJ84Feep79Hhm3E4zZJmnB

DESIGN.md

@@ -4929,10 +4929,18 @@ favour, against a measured ×4.06. **The connectivity fail is under-priced by
 roughly 3×, so the objective is net-positive on destroying the circulation
 spine even when the circulation is perfectly daylit.**
 
-That is the cleanest available explanation of why `level 0 not connected` and
-`level 1 not connected` are still present in the best layout found after
-1.7 M evals: the search is not failing to fix them, it is being paid ×3–4 to
-create them.
+**RETRACTED — see §39.8.** The inference above ("the objective is net-positive
+on severing the spine") does not survive measurement. It assumed severing costs
+exactly one failure; it does not. Every deletion that actually breaks
+connectivity is already punished — measured ×0.00 to ×0.58 across harbor-house
+and maple-court, not one rewarded. The ×4.06 figure above is real but was
+measured on a deletion that did **not** change the connectivity fail count, so
+it is not evidence for this mechanism. The deletions that are rewarded are
+rewarded because they remove the deleted leaf's OWN quality failures (7–9 of
+them), which is §38.1's zero-value finding, not a connectivity mispricing.
+
+Why `level 0/1 not connected` persist in the best layout is therefore still
+open, but it is not that the search is paid to create them.
 
 Together these retro-explain three prior results as one mechanism, and suggest
 two of them were measuring a broken gradient rather than a bad idea:
@@ -4960,6 +4968,14 @@ plot perimeter `private`**:
 | health-centre | 43 m | 41 m | feasible | §32 clean null | — |
 | programme-house | 24 m | 12 m | 2× surplus | — | **1 fail @ 12k evals** |
 
+**PARTLY RETRACTED — see §39.11.** The "2.7× / 2.9× short" figures below are
+computed for a **fully built plot**, which is not what these programmes ask
+for. Against actual demand the deficits are far smaller and both are closable:
+harbor needs 86 m against 54 m supplied (a 48 m² courtyard, with 304 m² of plot
+spare), maple 70 m against 56 m (20 m²). Neither is infeasible. The one
+programme that genuinely does not fit is health-centre, for an unrelated and
+much simpler reason: it demands 240 m² on a 197 m² plot.
+
 **Frontage deficit predicts the COST of solving, not impossibility.** An
 earlier draft of this section claimed the deficit predicts the plateau
 outright, quoting §13.11's 20k-budget figure as harbor's floor; that was
@@ -5059,10 +5075,16 @@ fails to move** — `homemaker-py-2v1` is the half that matters.
 rather than unmet") was aimed at the right target, and §38.3 supplies a cheap
 way to test it that does **not** need `2g7.1`'s traced human plans: the
 frontage bound is a pre-flight feasibility check computable from a plot and a
-programme alone. Two of the four corpus programmes fail it by ~3×, which means
-a share of the residual those runs are being judged on **is not reachable at
-all** — and any A/B measured against that residual has been measuring, in
-part, an unsatisfiable constraint.
+programme alone.
+
+*(As first written this paragraph continued "two of the four corpus programmes
+fail it by ~3×, which means a share of the residual those runs are being judged
+on is not reachable at all". **That is withdrawn** — see §39.11. The ~3× came
+from applying the bound to a fully built plot rather than to the area each
+programme demands; harbor-house and maple-court are frontage-feasible with room
+to spare. One programme is unsatisfiable, health-centre, and for a cruder
+reason: it demands 131% of its plot. So the residual the other runs are judged
+on is reachable, and the plateau is not explained by an unsatisfiable brief.)*
 
 Tracks 2 and 3 (cheaper evaluation, exact sub-solvers) remain sound but are
 orthogonal: making an evaluation 97× faster, or a labelling exact, does not
@@ -5073,6 +5095,12 @@ dominant mechanism, and the one the §38.6 A/B isolated) → `ssz`/`hxi`/`gvb`
 pre-flight bound and re-baseline the corpus), and only then resume
 `2g7.9`/`2g7.10`.
 
+*(Both halves of that ordering's rationale have since been measured and did not
+survive. `2v1` closed NULL — severing the spine is already punished, §38.2 is
+retracted — and `tdp`'s infeasibility claim is retracted above. What the
+ordering got right is that `ssz` comes before `2g7.7`; see §38.8 for what `ssz`
+turned out to be.)*
+
 **Acceptance test for the combined fix, stated up front so it cannot be
 moved:** harbor-house must reach its known 15-fail floor in materially fewer
 than 1.7 M evals, *and* `level 0 not connected` / `level 1 not connected` must
@@ -5083,6 +5111,180 @@ valley-crossing multi-edit against an objective that pays ×85 to delete the
 corridor it just inserted will have its work reverted by the next selection
 step.
 
+### 38.8 What `ssz` actually was: the objective demands daylight for rooms that do not need it (`homemaker-py-ssz`)
+
+**First, why §38.6's A/B does not stand.** It measured the three modes against
+the §38.2 *deletion test*, and it did so with a script that predates §39.4:
+`experiments/ab_crinkliness_mode_ssz.py` selected "unpinned" leaves with
+`(leaf.type or "")[:1].upper() in ("C", "O")`, the first-character prefix rule,
+so every programme room whose code happens to begin with c or o — `cr1`, `of1`
+— was swept in as circulation. Both the premise (§38.2, retracted) and the
+selection were wrong. The script is kept, with the prefix rule fixed and a
+warning in its docstring, but nothing is decided on its numbers.
+
+**Second, and simpler: none of the three modes ever touched the leaves `ssz` is
+about.** `quality_uncrinkliness` reaches `if not crink: return ...` *before* any
+of the mode logic that matters, so for a zero-exposure leaf:
+
+| mode | buried leaves | rescued to ≥ `FAIL_THRESHOLD` | windowless habitable rooms still failing |
+|---|---|---|---|
+| `urb` (stock) | 33 / 46 / 18 | 0% | 11/11, 13/13, 9/9 |
+| `floor` | 33 / 46 / 18 | 0% | 11/11, 13/13, 9/9 |
+| `compact_ok` *(as measured in §38.6)* | 33 / 46 / 18 | 0% | 11/11, 13/13, 9/9 |
+| `exempt_circulation` | 33 / 46 / 18 | 21% / 24% / 33% | 11/11, 13/13, 9/9 |
+
+*(harbor-house / maple-court / health-centre, 3 constructed seeds each, full
+default stack.)*
+
+`floor` returns 0.01 — one percent of a unit quality, multiplied into a product
+and weighed against a whole leaf's cost, which is why it reads as inert.
+`compact_ok` is worse than inert, it is **self-contradictory**: it announces
+that being more compact than target is not a defect, and then returns the floor
+for the most compact case of all, because `if not crink` fires before its clip
+is ever reached. Only `exempt_circulation` moves anything, and it reaches at
+most a third of the population. So §38.6's "none of them removes the incentive"
+was reading a null that the modes' own implementation guaranteed.
+
+**What the buried leaves actually are.** §39.7 gave every space a declared
+`usage:`, which lets the question be asked properly for the first time — of the
+leaves scoring a hard zero for want of daylight, how many are rooms a person
+sits in?
+
+| programme | buried | habitable (`living`/`kitchen`/`bedroom`) | store, toilet, plant, corridor, covered court |
+|---|---|---|---|
+| harbor-house | 33 | 11 (33%) | **22 (67%)** |
+| maple-court | 46 | 13 (28%) | **33 (72%)** |
+| health-centre | 18 | 9 (50%) | 9 (50%) |
+
+**Roughly two thirds of the zero-value leaves are spaces that architecturally
+do not want a window at all** — a broom cupboard, a WC, a plant room, an
+internal corridor, a covered courtyard. The objective scores them identically
+with a windowless bedroom. That is the miscalibration, and it is not a gradient
+problem to be patched with an epsilon; it is the wrong requirement applied to
+the wrong rooms.
+
+**The repair: `crinkliness_mode="usage_daylight"`.** Daylight is required of
+the uses a person occupies (`programme.DAYLIGHT_USAGES` =
+`living`/`kitchen`/`bedroom`) and of nothing else. For every other usage, and
+for the generic `C`/`O`/`S` types which carry no programme entry, the factor is
+clipped on the **compact side only** — being buried stops being a defect, while
+over-exposure still costs, because a crinkly leaf costs envelope whatever it is
+used for. A windowless bedroom remains exactly the hard zero it is under stock.
+
+| programme | buried | rescued by `usage_daylight` | windowless habitable rooms still failing |
+|---|---|---|---|
+| harbor-house | 33 | 22 (67%) | 11/11 |
+| maple-court | 46 | 33 (72%) | 13/13 |
+| health-centre | 18 | 9 (50%) | 9/9 |
+
+`compact_ok` was also repaired to score the buried limit as compact (1.0), the
+behaviour its name always claimed; it now rescues 100% and is kept as the
+**upper-bound control** — the mode that deletes the daylight requirement
+outright, including for bedrooms. It is not a candidate.
+
+**How this is scored, stated before the result.** `compact_ok`,
+`exempt_circulation` and `usage_daylight` all return 1.0 where stock returns
+below `FAIL_THRESHOLD`, so scoring an arm under its own objective deletes a fail
+category for free and every arm "wins". Every arm below is therefore optimised
+under its own objective and **re-scored under stock `urb`** — the comparable
+yardstick, and the only one that answers *did optimising under this variant
+steer the search to a better building?* The arm's own-objective count is
+reported alongside solely to show the size of the definitional discount. A mode
+passes on the stock column. `experiments/ab_ssz_search.py`.
+
+**The result: NOT A PASS at this budget, and n=3 cannot decide it.** Budget
+3000, 3 seeds, paired per-seed deltas against `urb` (negative = fewer fails):
+
+| mode | harbor hard Δ | mean | maple hard Δ | mean |
+|---|---|---|---|---|
+| `floor` | [0, −1, −2] | −1.0 | [+5, −2, −1] | +0.7 |
+| `compact_ok` | [0, −2, **−12**] | −4.7 | [0, +2, +1] | +1.0 |
+| `exempt_circulation` | [+2, −3, −1] | −0.7 | [0, +2, +1] | +1.0 |
+| `usage_daylight` | [0, −1, **−10**] | −3.7 | [0, +2, **−10**] | −2.7 |
+
+The means flatter every mode. **The whole signal is seed 2**, in both
+programmes, and seed 2 is the seed where stock itself does worst (harbor 22
+hard against 16/22; maple 51 against 30/23). Two seeds in three are flat or
+slightly worse. What this says is "on a bad run, the permissive modes do less
+badly" — which is not nothing, but it is not the claim.
+
+And on that seed the soft count rises by as much as the hard count falls:
+harbor seed 2 −10 hard / +9 soft, maple seed 2 −10 hard / +15 soft. **Totals**:
+harbor 62 → 61, maple 120 → **125**. Because every arm is scored under stock
+`urb`, this is a real change of layout and not a relabelling — the search
+genuinely traded hard failures for soft ones. Under the project's tiered
+comparator, where `n_hard` is the primary key, that trade is progress. Under
+`ssz`'s acceptance criterion — *lowers hard without inflating soft* — it is
+not. The criterion is stricter than the comparator the search actually uses;
+which of the two is the right yardstick is now the live question, and it is
+`homemaker-py-gvb`'s question as much as this one.
+
+`usage_daylight` stays **default off** pending a higher-powered run
+(`urb` vs `usage_daylight` only, more seeds, both programmes). Nothing here
+justifies shipping it as a default, and nothing here refutes it either: at
+n=3 with one dominant seed, the honest reading is *undecided*.
+
+**What is decided** is the diagnostic half, which does not depend on the search
+A/B: the daylight requirement is applied to rooms that architecturally do not
+want daylight, in two thirds of the buried population, and §38.6's contrary
+null was an artefact of three modes that never touched those leaves.
+
+### 38.9 Two corrections to §38.8, and the measurement that matters (`homemaker-py-ssz`)
+
+**Correction 1 — the A/B yardstick above is wrong.** §38.8 scores every arm
+under stock `urb`, reasoning that a permissive mode must not be allowed to win
+by deleting a fail category. That is sound only if stock is ground truth, and
+stock is exactly what this section shows is miscalibrated. Scoring the repair
+under the objective it repairs penalises it for repairing: stock counts a
+windowless broom cupboard as a failure, and the repair's whole purpose is to
+stop counting it. *Does the fix score well on the broken yardstick* is not a
+question worth answering, and the §38.8 A/B result should not be read as
+evidence against `usage_daylight`.
+
+**The measurement that does matter** asks whether the emitted failures are
+*true*, and needs no search at all (`experiments/audit_crinkliness_truth.py`).
+Of the `crinkliness` failures the stock objective reports, classified by the
+leaf's declared usage:
+
+| layout | crinkliness fails | on spaces that want no daylight |
+|---|---|---|
+| harbor-house, 3 constructed seeds | 67 | 41 (61%) |
+| maple-court, 3 constructed seeds | 112 | 68 (61%) |
+| health-centre, 3 constructed seeds | 20 | 10 (50%) |
+| harbor-house `generated.dom` (evolved) | 5 | 2 (40%) |
+| maple-court `generated.dom` (evolved) | 67 | 43 (64%) |
+| **overall** | **271** | **164 (61%)** |
+
+**61% of the crinkliness failures the objective reports are not defects**, and
+it holds on evolved artefacts, not just seeds. Under
+`value *= 0.5 ** len(failures)` every one of them halves the fitness of a design
+that has done nothing wrong — a design is punished for putting the store in the
+middle of the plan, which is what a competent architect does. That is a
+correctness fault, and it is not contingent on any A/B.
+
+**Correction 2 — `usage:` is the wrong key, and `usage_daylight` as written in
+§38.8 mis-keys it.** §39.7 established `usage:` as an *access-requirement*
+class. "Needs no special access" and "needs no window" are different questions,
+and the corpus separates them plainly:
+
+- `usage: none` is **Waiting Room**, **Reception**, **Reception Office**,
+  **Entrance Foyer** — a waiting room is a space people sit in for long
+  stretches and plainly wants daylight, yet `DAYLIGHT_USAGES` exempts it;
+- `usage: bedroom` is where the GP consulting rooms, counselling rooms and
+  staff offices live — all of which do want daylight, so that half is right,
+  but it is right by luck of how the access axis happened to fall.
+
+The audit is robust to the error (reclassifying `none` as wanting daylight
+moves the headline 61% → 57%), so the finding stands; the *design* does not.
+Daylight needs its own declared axis, per space, decided by the programme
+author exactly as `usage:` was — not derived from a different question that
+happens to correlate.
+
+`usage_daylight` therefore stays default off and is **not** the shipping fix.
+It is retained as the mechanism — the compact-side clip is the right shape for
+the factor — pending a `daylight:` attribute to key it on.
+
+
 ## 39. Config audit: requirements that actively fight the engine (`homemaker-py-ju3`) — measured 2026-08-25
 
 The corpus `patterns.config` targets and `costs.config` values were estimated
@@ -5422,3 +5624,277 @@ missed, because consulting rooms and storage stood in for them. With that
 substitution gone, `homemaker-py-2v1` (connectivity priced at ×0.5 against a ×6
 circulation→habitable value gap) is the remaining half of the same problem —
 and now measurable, because the fails it should be preventing actually fire.
+
+### 39.8 `homemaker-py-2v1` connectivity weighting — MEASURED NULL, premise retracted
+
+§38.2 concluded that the objective is net-positive on severing a level's
+circulation: merging a corridor into a habitable sibling gains
+`value_inside / value_circulation` = ×6, while `level N not connected` costs
+only ×0.5, so break-even needs `0.5^w < 50/300`, i.e. w > 2.58 — "severing must
+cost at least 3 fails and costs 1". **The arithmetic is right and the premise is
+wrong.**
+
+**What shipped anyway** (EXPERIMENTAL, default off, byte-identical):
+`fitness.connectivity_weight_for(value_inside, value_circulation)` returns the
+smallest weight making severing net-negative — 3.0 at the defaults, *derived*
+from the rates rather than hard-coded, so it tracks them if either is retuned.
+`conf["connectivity_weight"]` takes `1.0` (default, the flat rule), `"auto"`, or
+an explicit number, and counts each connectivity failure as w failures in the
+`0.5^n` penalty. `is_connectivity_fail` identifies the two strings.
+
+**The measurement.** At `auto` (=3) the §38.2 deletion test does not move at
+all: 5/25 deletions rewarded either way, median ×0.26 vs ×0.27. The reason is
+immediate once looked for — **the connectivity fail count is unchanged in every
+rewarded deletion**:
+
+| seed | deleted | | score | fails | connectivity fails |
+|---|---|---|---|---|---|
+| 0 | `rlrrr` `O` | buried | ×238 | 115 → 107 | 5 → **5** |
+| 0 | `rrrl` `O` | lit | ×346 | 115 → 106 | 5 → **5** |
+| 1 | `lrlll` `cr1` | lit | ×257 | 107 → 99 | 3 → **3** |
+| 2 | `rlrrl` `O` | buried | ×127 | 78 → 71 | 3 → **3** |
+
+Weighting a failure that never fires changes nothing. And when the deletion
+*does* break connectivity, the objective already punishes it — every such case
+across harbor-house and maple-court, 4 seeds each:
+
+| programme | deletions sampled | break connectivity | of those, rewarded |
+|---|---|---|---|
+| harbor-house | 32 | 2 | **0** (×0.00, ×0.01) |
+| maple-court | 32 | 5 | **0** (×0.58 … ×0.07) |
+
+So severing is already net-negative: it costs 1–2 connectivity failures *plus*
+the cascade that follows them (inaccessible space, broken adjacency), and that
+total already outweighs the ×6 value gain. The flat rule was never the problem.
+
+**Where §38.2 went wrong.** The ×4.06 "well-daylit circulation leaf" that
+motivated the whole bead was a deletion that did **not** change the
+connectivity fail count. It was rewarded for removing the leaf's own quality
+failures — §38.1's zero-value finding — and was misread as evidence for a
+pricing mechanism. Two lessons, both cheap to state and expensive to learn: a
+plausible closed-form arithmetic is not a measurement, and when a fix produces
+*exactly* no effect, suspect the premise before the implementation.
+
+**What is still true from §38.** §38.1 (buried leaves score a hard quality of
+zero and contribute no value) and §38.3 (the frontage budget) are direct
+measurements and stand. §39.7's finding — that the connectivity model was ~4×
+too permissive — also stands and is the more useful lever: it made the fails
+*fire*, where this bead would only have made them *cost more*.
+
+**Verdict: NULL.** The flag stays default off with this write-up, per house
+style for a measured-null lever. `homemaker-py-2v1` is closed. Why
+`level 0/1 not connected` survive in the best-known layout is re-opened as a
+question (`homemaker-py-yql`) — the evidence now says it is a reachability problem
+(connected topologies are hard to construct and hold onto), not an incentive
+one. It is newly measurable: §39.7 made the fails fire on constructed seeds
+instead of being hidden by routes through store cupboards.
+
+### 39.9 Why `level N not connected` persists: the resize destroys it (`homemaker-py-yql`)
+
+§39.8 closed `2v1` NULL — severing circulation is already punished, so the fail
+is not something the search is paid to create. That left the real question: is a
+connected layout **rarely constructed**, or **constructed and then lost**?
+
+**Answer: constructed, then lost — at construction time, in the resize.**
+
+`level N not connected` fires from `graph.connected_circulation`, which keeps
+only the generic `C`/`S` leaves and asks whether *they* form one component.
+Measured over 20 constructed seeds per programme
+(`experiments/diag_connectivity_yql.py`):
+
+| programme | levels connected | seeds fully connected |
+|---|---|---|
+| harbor-house | 21/40 (52%) | **1/20** |
+| health-centre | 1/20 (5%) | **1/20** |
+| maple-court | 39/60 (65%) | **0/20** |
+
+Then the decisive control — the same seeds with `proportion_aware=False`, i.e.
+skipping `_size_divisions_from_targets`:
+
+| programme | with resize | **without resize** |
+|---|---|---|
+| harbor-house | 52% | **100%** |
+| health-centre | 5% | **100%** |
+| maple-court | 65% | **100%** |
+
+`_assign_adjacency_aware` picks circulation as a **connected** dominating set —
+and it succeeds every time. The resize then moves every wall to hit the
+programme's area targets, and the shared boundaries the dominating set relied on
+shrink or vanish. On health-centre, **41 of 49 circulation-to-circulation edges
+are destroyed by the resize**, and surviving shared walls are squeezed to
+0.54–1.11 m against a 1.2 m `door_width`, so they stop counting as edges at all.
+
+This is exactly the failure mode §37.7 recorded for CP-SAT room assignment —
+"resizing can shrink a shared-wall segment below the door-width adjacency
+threshold, silently invalidating an edge the exact solve relied on" — but nobody
+had looked for it in **circulation connectivity**, where it costs 35–95 points.
+
+**§39.7 cost check: zero.** The same measurement under prefix-inferred vs
+declared usages is identical (52/5/65% both ways). `has_circulation` never trims
+`C`–`C` edges, so the usage change could not and did not make connectivity
+harder to achieve.
+
+#### The obvious repair is a net loss — measured
+
+`operators.repair_circulation_settled` applies §37.7's own alternating-
+minimisation fix: after the geometry settles, re-connect circulation by retyping
+the cheapest bridging leaves to `C` (preferring generic outside, then
+unassigned, crossing a required room last — `mutate_bridge_circulation`'s cost
+model). It works, completely:
+
+| programme | levels connected, repair OFF | repair ON |
+|---|---|---|
+| harbor-house | 52% (1/20 seeds full) | **100% (20/20)** |
+| health-centre | 5% (1/20) | **100% (20/20)** |
+| maple-court | 65% (0/20) | **100% (20/20)** |
+
+And it is still the wrong trade. Mean fails per constructed seed, 12 seeds:
+
+| programme | total | hard | connectivity | missing-room |
+|---|---|---|---|---|
+| harbor-house | 96.6 → **108.9** | 46.0 → 56.2 | 3.7 → 2.0 | 14.2 → **19.2** |
+| health-centre | 62.8 → **84.2** | 24.2 → 46.8 | 2.9 → 2.2 | 2.0 → **10.5** |
+| maple-court | 141.8 → **156.6** | 57.4 → 69.2 | 4.7 → 3.5 | 14.8 → **19.8** |
+
+Connectivity failures fall by 0.8–1.7; missing-room failures rise by 5.0–8.5,
+because every leaf retyped to `C` displaces a required room and each displacement
+costs a 3–5 fail cascade (§38.5). **Robbing Peter to pay Paul.** Kept default
+off with this write-up, per house style for a measured-null lever.
+
+**The lever is upstream, not downstream.** The repair is treating a symptom: the
+connection should never be destroyed in the first place. The named next move is
+to *preserve* it during the resize — constrain `_size_divisions_from_targets` so
+a shared boundary between two circulation leaves cannot fall below `door_width`
+— rather than to rebuild it afterwards at the cost of the programme. That is a
+constraint on an existing solve rather than a new repair pass. Filed as
+`homemaker-py-3z0`. Worth noting while there: `solver.py` already carries
+`min_width_generic` (default 1.2) to stop generic leaves collapsing to slivers
+— the same idea applied to a leaf's WIDTH rather than to a shared BOUNDARY
+between two specific leaves, so the new constraint may belong beside it.
+
+### 39.10 Preserving constructed connectivity through the resize (`homemaker-py-3z0`) — NULL, and it reframes §39.9
+
+§39.9 established that `_size_divisions_from_targets` destroys the connected
+circulation the seeder builds, and named the upstream fix: keep the connection
+*during* the resize rather than rebuilding it after. Built and measured. **It
+does not help, and the reason matters more than the lever.**
+
+**Both halves of the re-cut do damage, in different proportions per programme.**
+The resize changes each node's ratio *and* re-picks its rotation. Freezing the
+rotations and letting only the ratios move (12 seeds, % of levels connected):
+
+| programme | no resize | ratio only | full resize |
+|---|---|---|---|
+| harbor-house | 100% | 71% | 50% |
+| health-centre | 100% | **8%** | 8% |
+| maple-court | 100% | 92% | 67% |
+
+health-centre is destroyed entirely by the ratio; maple-court mostly by the
+rotation. So any fix has to be able to give back either.
+
+**`operators._size_divisions_preserving_circulation`** snapshots every cut,
+resizes, then reverts the cuts on the tree path between each
+circulation-to-circulation pair the resize broke. It keeps the programme
+completely intact — no retyping, no displacement, only geometry given back —
+and it works on connectivity:
+
+| programme | connected, OFF | ON | fails OFF → ON | hard OFF → ON |
+|---|---|---|---|---|
+| harbor-house | 50% | **92%** | 96.6 → **141.5** | 46.0 → 65.1 |
+| health-centre | 8% | 17% | 62.8 → **76.9** | 24.2 → 25.8 |
+| maple-court | 67% | **97%** | 141.8 → **175.8** | 57.4 → 70.9 |
+
+(A first attempt reverted greedily — whichever single cut most reduced the
+component count — and barely moved: it stalls on the plateau where no *one*
+revert helps though two would. Targeting the specific broken pairs is what
+made connectivity work.)
+
+Reverting a cut gives back that subtree's area accuracy, and size failures
+roughly double on harbor-house (5.2 → 11.4). The obvious defence is that these
+are raw constructed seeds and the inner loop has not run yet — the resize exists
+to *warm-start* the ratio optimiser, so a worse warm start might cost nothing
+once it converges. **Tested, and the defence fails.** Full search, harbor-house,
+12 000 evals, seed 1, both arms:
+
+| | fails | hard | soft | connectivity |
+|---|---|---|---|---|
+| `preserve_circulation` OFF | **43** | **9** | 34 | **3** |
+| `preserve_circulation` ON | 65 | 26 | 39 | 4 |
+
+Worse on every axis — including connectivity itself, the thing it was built to
+fix.
+
+**The reframing.** §39.9's finding stands as a fact (the resize really does
+destroy 41 of 49 circulation edges) but is **not actionable, because
+construction-time connectivity is not what determines final connectivity**. The
+search reaches 43 fails with 3 connectivity fails starting from a 50%-connected
+seed; forcing the seed to 92% connected yields 65 fails and 4 connectivity
+fails. The seeder's circulation topology is not the bottleneck — the search
+discards and rebuilds it either way, and constraining the seed only spends area
+quality the search then cannot recover.
+
+That also retires the framing this whole thread inherited from §38: connectivity
+was never a construction problem *or* an incentive problem (§39.8). Both flags
+(`repair_circulation`, `preserve_circulation`) stay default off with these
+numbers recorded. **Do not revisit either without a new formulation** — the same
+standing this document gives `bubble.py`.
+
+### 39.11 The frontage bound, computed correctly (`homemaker-py-tdp`) — shipped as a pre-flight check
+
+§38.3 derived a real constraint — every interior leaf needs
+`L >= A/(1.6202·h)` of daylit wall — and then applied it to the wrong quantity.
+It measured what a **fully built plot** would need. These programmes do not ask
+for a fully built plot.
+
+Recomputed against the area each programme actually demands:
+
+| programme | demanded/storey | % of plot | frontage needed | supplied | gap | courtyard to close | spare plot | |
+|---|---|---|---|---|---|---|---|---|
+| harbor-house | 418 m² | 60% | 86 m | 53 m | +33 m | 49 m² | 277 m² | **OK** |
+| maple-court | 338 m² | 44% | 70 m | 55 m | +15 m | 22 m² | 424 m² | **OK** |
+| programme-house | 38 m² | 72% | 8 m | 22 m | −14 m | none | — | **OK** |
+| health-centre | 240 m² | **131%** | 49 m | 41 m | +8 m | 12 m² | **−57 m²** | **DOES NOT FIT** |
+
+Plot area and frontage are measured through `geometry`, not from the raw
+`init.dom` corners, so they carry the `wall_outer` inset and the plot rotation —
+these are the metres and the square metres the leaves actually get. "Daylit"
+means what `Fitness.area_outside` means by it: an external boundary counts
+unless its perimeter type is `private` or `fortified`.
+
+So harbor-house and maple-court are **not** frontage-infeasible; they need a
+courtyard of 49 m² and 22 m² respectively, against 277 m² and 424 m² of spare
+plot. §38.3's "2.7× short" overstated it by comparing against a building nobody
+asked for.
+
+**The one genuinely infeasible programme is health-centre, and not for daylight
+reasons: it demands 240 m² of floor on a 183 m² plot.** That shows up
+unmistakably in the geometry — every room comes out at **0.60×** its declared
+target, 100% of them undersized, uniformly, no matter what the search does.
+Contrast harbor-house and maple-court, where the seeder hits targets almost
+exactly (median area / (target × share) = **1.01×**).
+
+*(An intermediate measurement suggested rooms were systematically inflated to
+1.26–1.65× target. That was an artefact of not dividing by a shared leaf's
+multiplicity — a leaf covering k rooms is legitimately k× a single target.
+Corrected above; the seeder's sizing is accurate where the plot allows.)*
+
+**Shipped: `evolve._preflight`.** Both checks now run at startup and print a
+warning before a multi-hour run bottoms out against something no amount of
+searching can fix:
+
+```
+WARNING: programme demands 240 m2 per storey on a 183 m2 plot (131%). Every room
+will be squeezed below its target however long the search runs.
+WARNING: 418 m2 per storey needs ~86 m of daylit wall; the plot's non-private
+perimeter gives 53 m. Roughly 49 m2 of courtyard closes the gap.
+```
+
+Advisory only — it never blocks a run, since an author may be deliberately
+exploring an over-tight brief. Silent on programme-house. The same numbers are
+available in full from `experiments/diag_exposure_frontage.py frontage`.
+
+**What this means for §38.** The frontage bound survives as a *diagnostic* and
+is now correctly calibrated, but it does **not** say the corpus is
+unsatisfiable. Of the four programmes, three fit their plots and one does not —
+and that one fails a much cruder test than daylight. §38.3's claim that the
+plateau programmes are "frontage-infeasible as specified" is withdrawn.

examples/harbor-house/evolved-3M-nols-3.dom

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+      rotation: 0
+      division:
+      - 0.0863852684329759
+      - 0.0863852684329759
+      l:
+        type: t
+        share: 3
+        rotation: 0
+      r:
+        rotation: 0
+        division:
+        - 0.369644807975687
+        - 0.369644807975687
+        l:
+          rotation: 0
+          division:
+          - 0.5
+          - 0.5
+          l:
+            rotation: 3
+            division:
+            - 0.5125
+            - 0.5125
+            l:
+              type: C
+              rotation: 0
+            r:
+              type: C
+              rotation: 0
+          r:
+            rotation: 1
+            division:
+            - 0.6910915096691898
+            - 0.6910915096691898
+            l:
+              type: O
+              rotation: 0
+            r:
+              type: C
+              rotation: 0
+        r:
+          type: n
+          share: 2
+          rotation: 0
+    r:
+      rotation: 0
+      division:
+      - 0.4566953630047795
+      - 0.4566953630047795
+      l:
+        rotation: 0
+        division:
+        - 0.16593799911395812
+        - 0.16593799911395812
+        l:
+          type: ut1
+          rotation: 0
+        r:
+          rotation: 3
+          division:
+          - 0.525234375
+          - 0.525234375
+          l:
+            type: C
+            rotation: 0
+          r:
+            type: C
+            rotation: 0
+      r:
+        rotation: 0
+        division:
+        - 0.2988974834269737
+        - 0.2988974834269737
+        l:
+          type: r
+          share: 3
+          rotation: 0
+        r:
+          rotation: 0
+          division:
+          - 0.5
+          - 0.5
+          l:
+            type: O
+            rotation: 0
+          r:
+            type: O
+            rotation: 0
+  r:
+    rotation: 0
+    division:
+    - 0.5670341721910087
+    - 0.5670341721910087
+    l:
+      rotation: 0
+      division:
+      - 0.5878540477469637
+      - 0.5878540477469637
+      l:
+        rotation: 0
+        division:
+        - 0.2988974834269737
+        - 0.2988974834269737
+        l:
+          type: r
+          share: 3
+          rotation: 0
+        r:
+          type: st2
+          rotation: 0
+      r:
+        rotation: 3
+        division:
+        - 0.5
+        - 0.5
+        l:
+          rotation: 3
+          division:
+          - 0.6580826806640626
+          - 0.6580826806640626
+          l:
+            rotation: 0
+            division:
+            - 0.5
+            - 0.5
+            l:
+              type: C
+              rotation: 0
+            r:
+              type: C
+              rotation: 0
+          r:
+            type: C
+            rotation: 0
+        r:
+          type: C
+          rotation: 0
+    r:
+      rotation: 0
+      division:
+      - 0.6164728327412322
+      - 0.6164728327412322
+      l:
+        type: r
+        rotation: 0
+      r:
+        rotation: 0
+        division:
+        - 0.6
+        - 0.6
+        l:
+          type: r
+          share: 3
+          rotation: 0
+        r:
+          type: li1
+          rotation: 0

experiments/ab_crinkliness_mode_ssz.py

@@ -16,6 +16,17 @@ buried or lit is what separates the two mechanisms:
   against a ×0.5 connectivity penalty (§38.2 refinement) — which no
   ``crinkliness_mode`` can touch.
 
+.. warning::
+
+   **The premise of this test is RETRACTED — see §38.2 and §38.8.** The ×6-vs-
+   ×0.5 arithmetic assumed severing the spine costs one connectivity fail;
+   measured, the connectivity count is unchanged in every rewarded deletion, so
+   this script is not measuring what its docstring says. It is kept because the
+   per-mode buried/lit split is still a useful description of what each mode
+   touches, but a mode does **not** pass or fail on these numbers. The A/B that
+   decides `ssz` is ``experiments/ab_ssz_search.py`` (fixed-budget search,
+   scored under the stock objective).
+
 Usage::
 
     python experiments/ab_crinkliness_mode_ssz.py
@@ -34,7 +45,8 @@ from homemaker_layout import driver, fitness, geometry
 from homemaker_layout import graph as graph_mod
 from homemaker_layout import operators, programme
 
-MODES = ("urb", "floor", "compact_ok", "exempt_circulation")
+MODES = ("urb", "floor", "compact_ok", "exempt_circulation",
+         "usage_daylight")
 
 
 def make_fitness(progdir: str, mode: str) -> fitness.Fitness:
@@ -74,7 +86,12 @@ def unpinned_leaves(fit: fitness.Fitness, root: dom_mod.Node) -> list[tuple]:
         for leaf in lvl.leaves():
             if dom_mod.is_outside(leaf) and not dom_mod.is_covered(leaf):
                 continue
-            if (leaf.type or "")[:1].upper() not in ("C", "O"):
+            # §39.4: generic structural types are EXACT `C`/`O`/`S`, never a
+            # first-character prefix -- `cr1` is a programme room. This script
+            # predates that rule and its original `type[:1].upper() in ("C","O")`
+            # test swept programme rooms into the "unpinned" set, which is one
+            # reason the §38.6 numbers do not reproduce.
+            if not dom_mod.is_generic(leaf.type):
                 continue
             out.append((li, leaf.id, leaf.type,
                         fit.area_outside(leaf, graphs[li], {})))

experiments/ab_ssz_search.py

@@ -0,0 +1,145 @@
+"""Fixed-budget search A/B for the crinkliness modes (`homemaker-py-ssz`).
+
+DESIGN.md §38.6 A/B'd the modes against the §38.2 *deletion test*, which has
+since been retracted, and it used the pre-§39.4 `type[:1] in ("C","O")` prefix
+rule that mislabels programme rooms as circulation. So the modes have never
+been measured against what `ssz`'s acceptance criteria actually asks for: a
+fixed-budget search, hard/soft fail split, on harbor-house and maple-court.
+
+**The scoring discipline is the point of this script.** `compact_ok`,
+`exempt_circulation` and `usage_daylight` all return 1.0 for leaves that stock
+scores below FAIL_THRESHOLD, so scoring an arm under its own objective deletes
+a fail category for free and every arm "wins". Two numbers are therefore
+reported per arm:
+
+  urb    the arm's final layout re-scored under the STOCK objective. This is
+         the comparable yardstick, and the one that answers "did optimising
+         under this variant steer the search to a better building?"
+  own    the same layout under the arm's own objective. Lower than `urb` by
+         construction for the permissive modes; it is reported only so the
+         size of the definitional discount is visible, never as the result.
+
+A mode passes on `urb`, not on `own`.
+
+Usage::
+
+    python experiments/ab_ssz_search.py --budget 3000 --seeds 3
+    python experiments/ab_ssz_search.py --modes urb usage_daylight --seeds 2
+"""
+
+from __future__ import annotations
+
+import argparse
+import collections
+import copy
+import csv
+import time
+from pathlib import Path
+
+from homemaker_layout import dom as dom_mod
+from homemaker_layout import driver, fitness
+
+CORPUS = ["examples/harbor-house", "examples/maple-court"]
+MODES = ["urb", "floor", "compact_ok", "exempt_circulation", "usage_daylight"]
+
+
+def _with_mode(mode: str):
+    """Patch `fitness.load_config` so every evaluator built during the run --
+    the driver's, the inner loop's, the seeder's -- sees `crinkliness_mode`.
+
+    `driver.search` has no parameter for it, and `driver._fitness_for` is
+    lru_cached on its arguments, so the cache is cleared around the patch or a
+    later arm would silently reuse the previous arm's evaluator.
+    """
+    orig = fitness.load_config
+
+    def patched(directory, overrides=None):
+        ov = dict(overrides or {})
+        ov["crinkliness_mode"] = mode
+        return orig(directory, overrides=ov)
+
+    return orig, patched
+
+
+def tiers(fails) -> tuple[int, int]:
+    c = collections.Counter(fitness.classify_fail_tier(f) for f in fails)
+    return c["hard"], c["soft"]
+
+
+def run_arm(progdir: str, seed: int, mode: str, budget: int,
+            child_budget: int) -> dict:
+    orig, patched = _with_mode(mode)
+    fitness.load_config = patched
+    driver._fitness_for.cache_clear()
+    t0 = time.perf_counter()
+    try:
+        res = driver.search(
+            dom_mod.load(f"{progdir}/init.dom"), progdir,
+            budget=budget, seed=seed, child_budget=child_budget, n_workers=1)
+        root = copy.deepcopy(res.best.root)
+        own_conf, own_cost = patched(progdir, overrides={"leaf_sharing": True,
+                                                         "collapse_insearch": True})
+        _, own_fails = fitness.Fitness(own_conf, own_cost).score_with_fails(
+            copy.deepcopy(root))
+    finally:
+        fitness.load_config = orig
+        driver._fitness_for.cache_clear()
+
+    # the comparable yardstick: stock objective, same layout
+    conf, cost = orig(progdir, overrides={"leaf_sharing": True,
+                                          "collapse_insearch": True})
+    _, urb_fails = fitness.Fitness(conf, cost).score_with_fails(copy.deepcopy(root))
+
+    uh, us = tiers(urb_fails)
+    oh, os_ = tiers(own_fails)
+    return dict(programme=Path(progdir).name, seed=seed, mode=mode,
+                urb_hard=uh, urb_soft=us, urb_total=uh + us,
+                own_hard=oh, own_soft=os_, own_total=oh + os_,
+                elapsed_s=round(time.perf_counter() - t0, 1))
+
+
+def main() -> None:
+    ap = argparse.ArgumentParser(description=__doc__,
+                                 formatter_class=argparse.RawDescriptionHelpFormatter)
+    ap.add_argument("--budget", type=int, default=3000)
+    ap.add_argument("--child-budget", type=int, default=80)
+    ap.add_argument("--seeds", type=int, default=3)
+    ap.add_argument("--modes", nargs="+", default=MODES)
+    ap.add_argument("--corpus", nargs="+", default=CORPUS)
+    ap.add_argument("--out", default="experiments/results/ab_ssz_search.csv")
+    args = ap.parse_args()
+
+    rows = []
+    out = Path(args.out)
+    out.parent.mkdir(parents=True, exist_ok=True)
+    for progdir in args.corpus:
+        for mode in args.modes:
+            for seed in range(args.seeds):
+                r = run_arm(progdir, seed, mode, args.budget, args.child_budget)
+                rows.append(r)
+                print(f"  {r['programme']:<14} {mode:<20} seed={seed} "
+                      f"urb {r['urb_hard']}h/{r['urb_soft']}s "
+                      f"(own {r['own_hard']}h/{r['own_soft']}s) "
+                      f"{r['elapsed_s']}s", flush=True)
+                with out.open("w", newline="") as fh:
+                    w = csv.DictWriter(fh, fieldnames=list(rows[0]))
+                    w.writeheader()
+                    w.writerows(rows)
+
+    print(f"\n=== stock-objective (urb) fail counts, budget {args.budget} ===")
+    print(f"  {'programme':<14}{'mode':<22}{'hard':<14}{'soft':<14}total")
+    print("  " + "-" * 70)
+    for progdir in args.corpus:
+        name = Path(progdir).name
+        for mode in args.modes:
+            sel = [r for r in rows if r["programme"] == name and r["mode"] == mode]
+            if not sel:
+                continue
+            h = sum(r["urb_hard"] for r in sel) / len(sel)
+            s = sum(r["urb_soft"] for r in sel) / len(sel)
+            print(f"  {name:<14}{mode:<22}{h:<14.1f}{s:<14.1f}{h + s:.1f}")
+    print(f"\nwrote {out}")
+
+
+if __name__ == "__main__":
+    main()

experiments/audit_crinkliness_truth.py

@@ -0,0 +1,132 @@
+"""Are the crinkliness failures the objective emits real defects? (`homemaker-py-ssz`)
+
+Not an A/B. This asks a correctness question the search cannot answer: of the
+`crinkliness` failures the STOCK objective reports, how many are on a space
+that architecturally wants daylight at all?
+
+A `crinkliness` fail says "this leaf has too little exposed wall for its area".
+For a bedroom or a living room that is a real defect. For a broom cupboard, a
+WC, a plant room, an internal corridor or a covered courtyard it is not -- those
+are ordinary buried architecture, and the fail is an artefact of applying one
+daylight requirement to every space regardless of use (DESIGN.md §38.8).
+
+Every fail is classified by the leaf's DECLARED `usage:` (§39.7), so nothing
+here rests on how a code is spelled.
+
+Usage::
+
+    python experiments/audit_crinkliness_truth.py
+    python experiments/audit_crinkliness_truth.py --seeds 5
+    python experiments/audit_crinkliness_truth.py --dom examples/harbor-house/generated.dom
+"""
+
+from __future__ import annotations
+
+import argparse
+import collections
+import copy
+from pathlib import Path
+
+import numpy as np
+
+from homemaker_layout import dom as dom_mod
+from homemaker_layout import driver, fitness, geometry
+from homemaker_layout import graph as graph_mod
+from homemaker_layout import operators, programme
+
+CORPUS = ["examples/harbor-house", "examples/maple-court", "examples/health-centre"]
+
+
+def stock_fitness(progdir: str) -> fitness.Fitness:
+    """Stock objective -- `crinkliness_mode` left at its "urb" default."""
+    ov = dict(driver._overrides_for(
+        leaf_sharing=True, superpose=False, max_share=None, conn_grade=False,
+        collapse_insearch=True, multi_use=False) or {})
+    conf, cost = fitness.load_config(progdir, overrides=ov)
+    return fitness.Fitness(conf, cost)
+
+
+def constructed(progdir: str, s: int) -> dom_mod.Node:
+    reqs = programme.load_programme_dir(progdir)
+    return operators.constructive_topology(
+        dom_mod.load(f"{progdir}/init.dom"), reqs, np.random.default_rng(s),
+        sorted(reqs) + ["C", "O"], min_storeys=programme.storey_minimum(progdir),
+        adjacency_aware=True, proportion_aware=True, circ_divisor=3,
+        leaf_sharing=True, leaf_share_factor=3, depth_balanced=True,
+        interior_outside=True, outside_divisor=3)
+
+
+def audit(fit: fitness.Fitness, root: dom_mod.Node) -> collections.Counter:
+    """usage -> count, over the leaves that emit a stock `crinkliness` fail."""
+    tree = copy.deepcopy(root)
+    geometry.clear_cache()
+    dom_mod.canonicalize_shares(tree)
+    fit.preprocess_building(tree)
+    dom_mod.merge_divided(tree)
+    geometry.clear_cache()
+    graphs = graph_mod.build_graphs(tree, fit.conf("door_width") or 1.2)
+
+    out: collections.Counter = collections.Counter()
+    for li, lvl in enumerate(dom_mod.levels(tree)):
+        groups = geometry.boundary_groups(lvl)
+        for leaf in lvl.leaves():
+            if dom_mod.is_outside(leaf) and not dom_mod.is_covered(leaf):
+                continue
+            if fit.quality_uncrinkliness(leaf, graphs[li], groups) >= fitness.FAIL_THRESHOLD:
+                continue                       # not a failure
+            out[fit.usage_of(leaf) or f"<generic {leaf.type}>"] += 1
+    return out
+
+
+def report(label: str, tally: collections.Counter) -> tuple[int, int]:
+    total = sum(tally.values())
+    real = sum(n for u, n in tally.items() if u in programme.DAYLIGHT_USAGES)
+    print(f"=== {label}: {total} crinkliness fails")
+    if not total:
+        print("    none\n")
+        return 0, 0
+    for usage, n in tally.most_common():
+        verdict = ("REAL DEFECT" if usage in programme.DAYLIGHT_USAGES
+                   else "not a defect -- no daylight wanted")
+        print(f"    {usage:<18}{n:>4}   {verdict}")
+    print(f"    -> {total - real}/{total} ({100 * (total - real) / total:.0f}%) "
+          f"are reported against spaces that do not want daylight\n")
+    return real, total
+
+
+def main() -> None:
+    ap = argparse.ArgumentParser(description=__doc__,
+                                 formatter_class=argparse.RawDescriptionHelpFormatter)
+    ap.add_argument("--seeds", type=int, default=3)
+    ap.add_argument("--corpus", nargs="+", default=CORPUS)
+    ap.add_argument("--dom", nargs="*", default=[],
+                    help="also audit these evolved .dom files (programme dir inferred)")
+    args = ap.parse_args()
+
+    print("Stock objective. Every fail classified by the leaf's declared usage.\n")
+    grand_real = grand_total = 0
+
+    for progdir in args.corpus:
+        fit = stock_fitness(progdir)
+        tally: collections.Counter = collections.Counter()
+        for s in range(args.seeds):
+            tally += audit(fit, constructed(progdir, s))
+        r, t = report(f"{Path(progdir).name} ({args.seeds} constructed seeds)", tally)
+        grand_real += r
+        grand_total += t
+
+    for dom_path in args.dom:
+        progdir = str(Path(dom_path).parent)
+        fit = stock_fitness(progdir)
+        r, t = report(f"{dom_path} (evolved)", audit(fit, dom_mod.load(dom_path)))
+        grand_real += r
+        grand_total += t
+
+    if grand_total:
+        print(f"OVERALL: {grand_total - grand_real}/{grand_total} "
+              f"({100 * (grand_total - grand_real) / grand_total:.0f}%) of the "
+              f"crinkliness failures the objective reports are not defects.")
+
+
+if __name__ == "__main__":
+    main()

experiments/diag_connectivity_yql.py

@@ -0,0 +1,167 @@
+"""Why does `level N not connected` persist? (`homemaker-py-yql`, DESIGN.md §39.9)
+
+`homemaker-py-2v1` closed NULL: severing a level's circulation is already
+punished, so the fail is not something the search is paid to create. This asks
+the follow-on question — is a connected layout **rarely constructed**, or
+**constructed and then lost**?
+
+`level N not connected` fires from `graph.connected_circulation`, which keeps
+only the generic circulation leaves (`C`/`S`) and asks whether *they* form one
+connected component. It runs on `graph_circ`, i.e. AFTER
+`graph.has_circulation` has trimmed edges, so §39.7's usage change can in
+principle reach it — report (b) measures whether it did.
+
+Three reports:
+
+  construct  what fraction of constructed seeds start connected, per level
+  cost       the same, prefix-inferred usages vs declared (the §39.7 cost)
+  survive    from a CONNECTED layout, how often does one mutation break
+             connectivity, and would the outer comparator keep the mutant
+
+Usage::
+
+    python experiments/diag_connectivity_yql.py construct
+    python experiments/diag_connectivity_yql.py cost
+    python experiments/diag_connectivity_yql.py survive --seeds 40
+"""
+
+from __future__ import annotations
+
+import argparse
+import copy
+from pathlib import Path
+
+import numpy as np
+
+from homemaker_layout import dom as dom_mod
+from homemaker_layout import driver, fitness, geometry
+from homemaker_layout import graph as graph_mod
+from homemaker_layout import operators, programme
+
+CORPUS = ["examples/harbor-house", "examples/health-centre", "examples/maple-court"]
+LEGACY_PREFIX = {"b": "bedroom", "t": "toilet", "l": "living", "k": "kitchen"}
+
+
+def make_fitness(progdir: str) -> fitness.Fitness:
+    overrides = driver._overrides_for(
+        leaf_sharing=True, superpose=False, max_share=None, conn_grade=False,
+        collapse_insearch=True, multi_use=False)
+    conf, cost = fitness.load_config(progdir, overrides=dict(overrides or {}))
+    return fitness.Fitness(conf, cost)
+
+
+def constructed_seed(progdir: str, seed: int) -> dom_mod.Node:
+    reqs = programme.load_programme_dir(progdir)
+    return operators.constructive_topology(
+        dom_mod.load(f"{progdir}/init.dom"), reqs, np.random.default_rng(seed),
+        sorted(reqs) + ["C", "O"],
+        min_storeys=programme.storey_minimum(progdir),
+        adjacency_aware=True, proportion_aware=True, circ_divisor=3,
+        leaf_sharing=True, leaf_share_factor=3, depth_balanced=True,
+        interior_outside=True, outside_divisor=3)
+
+
+def connectivity(root: dom_mod.Node, usages: dict[str, str]) -> tuple[int, int]:
+    """``(levels_connected, levels_total)`` for one tree.
+
+    Mirrors the scorer: build the circ graphs, then ask
+    ``connected_circulation`` per level on a copy, exactly as
+    ``process_storey`` does.
+    """
+    tree = copy.deepcopy(root)
+    geometry.clear_cache()
+    dom_mod.canonicalize_shares(tree)
+    _, circ = graph_mod.build_graphs_with_circ(tree, 1.2, lambda _f: None, usages)
+    connected = sum(1 for gc in circ
+                    if graph_mod.connected_circulation(gc.copy()))
+    return connected, len(circ)
+
+
+def report_construct(seeds: int) -> None:
+    print(f"how often does a CONSTRUCTED seed start connected? ({seeds} seeds)\n")
+    print(f"  {'programme':<18}{'levels connected':<20}{'seeds fully connected'}")
+    print("  " + "-" * 62)
+    for progdir in CORPUS:
+        fit = make_fitness(progdir)
+        usages = fit.usages()
+        ok = tot = full = 0
+        for s in range(seeds):
+            c, n = connectivity(constructed_seed(progdir, s), usages)
+            ok += c
+            tot += n
+            full += (c == n)
+        print(f"  {Path(progdir).name:<18}{f'{ok}/{tot} ({100*ok/max(tot,1):.0f}%)':<20}"
+              f"{full}/{seeds}")
+
+
+def report_cost(seeds: int) -> None:
+    """Did §39.7's usage change make level connectivity harder to achieve?"""
+    print("§39.7 cost check — prefix-inferred usages vs declared "
+          f"({seeds} seeds)\n")
+    print(f"  {'programme':<18}{'prefix-inferred':<20}{'declared':<20}delta")
+    print("  " + "-" * 68)
+    for progdir in CORPUS:
+        reqs = programme.load_programme_dir(progdir)
+        declared = {c: r.usage for c, r in reqs.items()}
+        legacy = {c: LEGACY_PREFIX.get(c[:1].lower(), "none") for c in reqs}
+        res = {}
+        for label, usages in (("legacy", legacy), ("declared", declared)):
+            ok = tot = 0
+            for s in range(seeds):
+                c, n = connectivity(constructed_seed(progdir, s), usages)
+                ok += c
+                tot += n
+            res[label] = (ok, tot)
+        (a, ta), (b, tb) = res["legacy"], res["declared"]
+        delta = 100 * b / max(tb, 1) - 100 * a / max(ta, 1)
+        print(f"  {Path(progdir).name:<18}"
+              f"{f'{a}/{ta} ({100*a/max(ta,1):.0f}%)':<20}"
+              f"{f'{b}/{tb} ({100*b/max(tb,1):.0f}%)':<20}{delta:+.0f} pts")
+
+
+def report_survive(seeds: int) -> None:
+    """From a CONNECTED level, how fragile is that connectivity under one
+    mutation — and would the comparator keep the mutant anyway?"""
+    print(f"survival of connectivity under one mutation ({seeds} trials)\n")
+    print(f"  {'programme':<18}{'started connected':<20}{'broken by mutation':<22}"
+          f"{'…and kept by comparator'}")
+    print("  " + "-" * 82)
+    for progdir in CORPUS:
+        fit = make_fitness(progdir)
+        usages = fit.usages()
+        reqs = programme.load_programme_dir(progdir)
+        types = sorted(reqs) + ["C", "O"]
+        started = broken = kept = 0
+        rng = np.random.default_rng(0)
+        for s in range(seeds):
+            root = constructed_seed(progdir, s)
+            c, n = connectivity(root, usages)
+            if c != n:
+                continue                      # only study layouts that ARE connected
+            started += 1
+            base_score, base_fails = fit.score_with_fails(copy.deepcopy(root))
+            child, _desc = operators.mutate(root, rng, types, reqs=reqs)
+            c2, n2 = connectivity(child, usages)
+            if c2 == n2:
+                continue
+            broken += 1
+            # would the outer loop admit it? lexicographic (-n_fails, fitness)
+            score, fails = fit.score_with_fails(copy.deepcopy(child))
+            if (-len(fails), score) > (-len(base_fails), base_score):
+                kept += 1
+        print(f"  {Path(progdir).name:<18}{f'{started}/{seeds}':<20}"
+              f"{f'{broken}/{max(started,1)}':<22}{kept}")
+
+
+def main() -> None:
+    ap = argparse.ArgumentParser(description=__doc__,
+                                 formatter_class=argparse.RawDescriptionHelpFormatter)
+    ap.add_argument("report", choices=("construct", "cost", "survive"))
+    ap.add_argument("--seeds", type=int, default=20)
+    args = ap.parse_args()
+    {"construct": report_construct, "cost": report_cost,
+     "survive": report_survive}[args.report](args.seeds)
+
+
+if __name__ == "__main__":
+    main()

experiments/diag_exposure_frontage.py

@@ -35,7 +35,6 @@ import math
 from pathlib import Path
 
 import numpy as np
-import yaml
 
 from homemaker_layout import dom as dom_mod
 from homemaker_layout import driver, fitness, geometry
@@ -176,6 +175,53 @@ def report_value(progdir: str, seed: int, limit: int) -> None:
               f"({verdict}), fails {len(base_fails)} -> {len(fails)}")
 
 
+def frontage_budget(progdir: str) -> dict:
+    """Feasibility of a programme on its plot, before any search runs.
+
+    Two independent checks, in the order they bite:
+
+    1. **Does the programme fit the plot at all?** ``demand / storeys`` against
+       the plot area. health-centre asks for 240 m² on a 183 m² plot — 131% —
+       and every room comes out at 0.60x its target no matter what the search
+       does.
+    2. **Is there enough daylit wall for the area it does demand?** Every
+       interior leaf needs ``L >= A/(X*h)`` (§38.3), so a storey building
+       ``A_built`` needs ``A_built/(X*h)`` metres. The plot's non-``private``
+       perimeter supplies some; interior courtyard supplies the rest, at roughly
+       ``2 * area / width`` metres per courtyard slot.
+
+    NB this must be computed against the area the programme actually DEMANDS,
+    not a fully built plot — see §39.11 for the correction.
+    """
+    root = dom_mod.load(f"{progdir}/init.dom")
+    per = root.perimeter or {}
+    height = root.height or 3.0
+    # measured exactly as `Fitness.area_outside` does: an external boundary is
+    # daylit unless its perimeter type is `private` or `fortified`. Going
+    # through `geometry` rather than the raw YAML corners also picks up the
+    # `wall_outer` inset and the plot rotation, so these are the metres and the
+    # square metres the leaves actually get.
+    daylit = sum(geometry.edge_length(root, e) for e in range(4)
+                 if (per.get(geometry.boundary_id(root, e)) or "").lower()
+                 not in ("private", "fortified"))
+    plot = geometry.area(root)
+    reqs = programme.load_programme_dir(progdir)
+    storeys = max(programme.n_storeys_required(reqs),
+                  programme.storey_minimum(progdir))
+    demand = sum(r.size * r.count for r in reqs.values())
+    built = demand / storeys
+    x_buried, _ = fail_bounds()
+    needed = built / (x_buried * height)
+    gap = needed - daylit
+    court = max(0.0, gap) * 3.0 / 2.0          # 3 m courtyard slots
+    spare = plot - built
+    return dict(plot=plot, daylit=daylit, height=height, storeys=storeys,
+                demand=demand, built=built, needed=needed, gap=gap,
+                court=court, spare=spare,
+                fits_plot=built <= plot,
+                frontage_ok=court <= spare)
+
+
 def report_frontage(progdirs: list[str]) -> None:
     x_buried, x_exposed = fail_bounds()
     print(f"crinkliness fails when 1/crink > {x_buried:.4f} (buried) "
@@ -183,35 +229,23 @@ def report_frontage(progdirs: list[str]) -> None:
     print(f"=> every interior leaf needs exposed wall L >= A / ({x_buried:.4f} * h)\n")
 
     for progdir in progdirs:
-        seed = yaml.safe_load(open(f"{progdir}/init.dom"))
-        corners, per = seed["node"], (seed.get("perimeter") or {})
-        height = seed.get("height") or 3.0
-        n = len(corners)
-        edges = [math.hypot(corners[(i + 1) % n][0] - corners[i][0],
-                            corners[(i + 1) % n][1] - corners[i][1]) for i in range(n)]
-        daylit = sum(e for k, e in zip("abcd", edges)
-                     if (per.get(k) or "").lower() not in ("private", "fortified"))
-        area = abs(sum(corners[i][0] * corners[(i + 1) % n][1]
-                       - corners[(i + 1) % n][0] * corners[i][1]
-                       for i in range(n))) / 2
-        reqs = programme.load_programme_dir(progdir)
-        n_storeys = max(programme.n_storeys_required(reqs),
-                        programme.storey_minimum(progdir))
-        demand = sum(r.size * r.count for r in reqs.values())
-        needed = area / (x_buried * height)
-
+        b = frontage_budget(progdir)
         print(f"=== {Path(progdir).name}")
-        print(f"  plot {area:.0f} m2, perimeter {sum(edges):.0f} m, "
-              f"{n_storeys} storeys, h={height}")
-        print(f"  perimeter {per} -> daylit frontage {daylit:.0f} m")
-        print(f"  a fully built storey needs {needed:.0f} m exposed wall; "
-              f"plot supplies {daylit:.0f} m "
-              f"-> {needed / max(daylit, 1e-9):.1f}x short"
-              if needed > daylit else
-              f"  a fully built storey needs {needed:.0f} m exposed wall; "
-              f"plot supplies {daylit:.0f} m -> FEASIBLE")
-        print(f"  programme demands {demand:.0f} m2 over {n_storeys} storeys "
-              f"({demand / n_storeys:.0f} m2/storey of {area:.0f} m2 plot)\n")
+        print(f"  plot {b['plot']:.0f} m2, daylit perimeter {b['daylit']:.0f} m, "
+              f"{b['storeys']} storeys, h={b['height']:g}")
+        pct = 100 * b["built"] / b["plot"]
+        verdict = "OK" if b["fits_plot"] else "DOES NOT FIT THE PLOT"
+        print(f"  1. programme demands {b['demand']:.0f} m2 -> {b['built']:.0f} m2 "
+              f"per storey = {pct:.0f}% of the plot   [{verdict}]")
+        print(f"  2. that needs {b['needed']:.0f} m of daylit wall; perimeter gives "
+              f"{b['daylit']:.0f} m -> gap {b['gap']:+.0f} m")
+        if b["gap"] > 0:
+            print(f"     closing it takes ~{b['court']:.0f} m2 of 3 m courtyard; "
+                  f"spare plot {b['spare']:.0f} m2   "
+                  f"[{'OK' if b['frontage_ok'] else 'NOT ENOUGH ROOM'}]")
+        else:
+            print("     perimeter alone is sufficient")
+        print()
 
 
 def main() -> None:

experiments/results/ab_ssz_power.csv

@@ -0,0 +1,7 @@
+programme,seed,mode,urb_hard,urb_soft,urb_total,own_hard,own_soft,own_total,elapsed_s
+harbor-house,0,urb,16,39,55,16,39,55,76.4
+harbor-house,1,urb,22,45,67,22,45,67,80.8
+harbor-house,2,urb,22,40,62,22,40,62,76.6
+harbor-house,3,urb,15,48,63,15,48,63,75.2
+harbor-house,4,urb,17,42,59,17,42,59,83.9
+harbor-house,5,urb,29,42,71,29,42,71,81.7

experiments/results/ab_ssz_search.csv

@@ -0,0 +1,31 @@
+programme,seed,mode,urb_hard,urb_soft,urb_total,own_hard,own_soft,own_total,elapsed_s
+harbor-house,0,urb,16,39,55,16,39,55,80.2
+harbor-house,1,urb,22,45,67,22,45,67,88.7
+harbor-house,2,urb,22,40,62,22,40,62,79.8
+harbor-house,0,floor,16,38,54,16,38,54,78.9
+harbor-house,1,floor,21,46,67,21,46,67,82.9
+harbor-house,2,floor,20,41,61,20,41,61,79.0
+harbor-house,0,compact_ok,16,39,55,16,22,38,78.7
+harbor-house,1,compact_ok,20,44,64,20,20,40,82.6
+harbor-house,2,compact_ok,10,55,65,10,34,44,81.4
+harbor-house,0,exempt_circulation,18,37,55,18,34,52,77.2
+harbor-house,1,exempt_circulation,19,49,68,19,42,61,81.0
+harbor-house,2,exempt_circulation,21,42,63,21,37,58,79.0
+harbor-house,0,usage_daylight,16,39,55,16,30,46,79.9
+harbor-house,1,usage_daylight,21,51,72,21,30,51,82.3
+harbor-house,2,usage_daylight,12,49,61,12,35,47,81.8
+maple-court,0,urb,30,77,107,30,77,107,108.5
+maple-court,1,urb,23,83,106,23,83,106,109.0
+maple-court,2,urb,51,69,120,51,69,120,110.1
+maple-court,0,floor,35,74,109,35,74,109,109.1
+maple-court,1,floor,21,81,102,21,81,102,107.9
+maple-court,2,floor,50,69,119,50,69,119,110.3
+maple-court,0,compact_ok,30,78,108,30,47,77,109.8
+maple-court,1,compact_ok,25,82,107,25,43,68,108.6
+maple-court,2,compact_ok,52,70,122,52,33,85,105.9
+maple-court,0,exempt_circulation,30,72,102,30,66,96,105.1
+maple-court,1,exempt_circulation,25,81,106,25,70,95,106.6
+maple-court,2,exempt_circulation,52,70,122,52,61,113,112.6
+maple-court,0,usage_daylight,30,69,99,30,52,82,110.3
+maple-court,1,usage_daylight,25,73,98,25,56,81,107.9
+maple-court,2,usage_daylight,41,84,125,41,59,100,113.2

src/homemaker_layout/driver.py

@@ -316,6 +316,7 @@ def search(
     shapecurve_prune: bool = False,
     assign_solver: str = "greedy",
     enable_reassign: bool = False,
+    preserve_circulation: bool = False,
 ) -> SearchResult:
     """Run the memetic loop from ``seed_root`` until ``budget`` oracle
     evaluations are consumed. Returns the best individual found; its ``root``
@@ -630,7 +631,8 @@ def search(
                 depth_balanced=depth_balanced,
                 interior_outside=interior_outside, outside_divisor=outside_divisor,
                 construction_beam_width=construction_beam_width,
-                multi_use=multi_use, assign_solver=assign_solver)
+                multi_use=multi_use, assign_solver=assign_solver,
+                preserve_circulation=preserve_circulation)
             return (topo, None, child_budget, {}, f"construct/{tag}")
         n = int(rng.integers(max(1, n_target - 1), n_target + 2))
         return (random_topology(seed_root, n, rng, types), None, child_budget,

src/homemaker_layout/evolve.py

@@ -223,6 +223,60 @@ def _parse_args(argv=None) -> argparse.Namespace:
     return p.parse_args(argv)
 
 
+def _preflight(programme_dir) -> None:
+    """Warn before the run if the programme cannot fit its plot (homemaker-py-tdp).
+
+    Two checks, cheap and closed-form (DESIGN.md §38.3/§39.11). Neither can be
+    fixed by searching harder, so it is worth saying so up front rather than
+    letting a multi-hour run bottom out against it:
+
+    1. does the demanded floor area fit the plot at all;
+    2. is there enough daylit wall for that area, given every interior leaf
+       needs ``L >= A/(1.6202*h)`` before it fails crinkliness.
+
+    "Daylit" is measured exactly as ``Fitness.area_outside`` does: an external
+    boundary counts unless its perimeter type is ``private`` or ``fortified``.
+
+    Advisory only — it never blocks a run, since an author may deliberately be
+    exploring an over-tight brief.
+    """
+    from . import geometry
+    from . import programme as _prog
+
+    try:
+        root = dom.load(f"{programme_dir}/init.dom")
+        per = root.perimeter or {}
+        daylit = sum(geometry.edge_length(root, e) for e in range(4)
+                     if (per.get(geometry.boundary_id(root, e)) or "").lower()
+                     not in ("private", "fortified"))
+        plot = geometry.area(root)
+        height = root.height or 3.0
+        reqs = _prog.load_programme_dir(str(programme_dir))
+        storeys = max(_prog.n_storeys_required(reqs),
+                      _prog.storey_minimum(str(programme_dir)))
+        built = sum(r.size * r.count for r in reqs.values()) / max(storeys, 1)
+    except Exception:
+        return                              # advisory only; never block a run
+
+    if not plot or not daylit:
+        return
+
+    if built > plot:
+        print(f"WARNING: programme demands {built:.0f} m2 per storey on a "
+              f"{plot:.0f} m2 plot ({100 * built / plot:.0f}%). Every room will "
+              f"be squeezed below its target however long the search runs. "
+              f"(DESIGN.md §39.11)", file=sys.stderr)
+    needed = built / (1.6202 * height)
+    if needed > daylit:
+        court = (needed - daylit) * 1.5
+        note = (f", but only {plot - built:.0f} m2 of plot is spare"
+                if court > plot - built else "")
+        print(f"WARNING: {built:.0f} m2 per storey needs ~{needed:.0f} m of daylit "
+              f"wall; the plot's non-private perimeter gives {daylit:.0f} m. "
+              f"Roughly {court:.0f} m2 of courtyard closes the gap{note}. "
+              f"(DESIGN.md §38.3)", file=sys.stderr)
+
+
 def main(argv=None) -> int:
     args = _parse_args(argv)
 
@@ -246,6 +300,8 @@ def main(argv=None) -> int:
     else:
         out = args.output.resolve()
 
+    _preflight(programme_dir)
+
     print(f"seed         : {seed_file}", file=sys.stderr)
     print(f"programme    : {programme_dir.name}", file=sys.stderr)
     print(f"budget       : {args.budget}", file=sys.stderr)

src/homemaker_layout/fitness.py

@@ -118,6 +118,40 @@ _SOFT_FAIL_MARKERS = (
 )
 
 
+# homemaker-py-2v1 (DESIGN.md §39.8) — the fails that punish severing a level's
+# circulation. These are the ONLY counter-pressure against a structural x6 gain:
+# deleting a circulation leaf merges it into its sibling, converting corridor
+# into habitable area, and value_inside/value_circulation is 300/50.
+_CONNECTIVITY_FAIL_MARKERS = ("not connected", "inaccessible usable space")
+
+
+def is_connectivity_fail(fail: str) -> bool:
+    """True for a level-connectivity failure (``level N not connected`` /
+    ``N inaccessible usable space``)."""
+    return any(m in fail for m in _CONNECTIVITY_FAIL_MARKERS)
+
+
+def connectivity_weight_for(value_inside: float, value_circulation: float) -> float:
+    """Smallest integer weight at which severing circulation is net-NEGATIVE.
+
+    Merging a circulation leaf into a habitable sibling multiplies value by
+    ``value_inside / value_circulation`` (x6 at the defaults). One failure costs
+    x0.5. So the penalty only outweighs the gain once
+    ``0.5**w < value_circulation / value_inside``, i.e.
+    ``w > log(vc/vi) / log(0.5)`` — 2.58 at the defaults, hence 3.
+
+    Derived from the value rates rather than hard-coded, so the two stay in step
+    if either rate is ever retuned.
+    """
+    import math
+    if value_inside <= 0 or value_circulation <= 0:
+        return 1.0
+    ratio = value_circulation / value_inside
+    if ratio >= 1.0:                      # circulation already worth as much
+        return 1.0
+    return float(math.ceil(math.log(ratio) / math.log(0.5)))
+
+
 def classify_fail_tier(fail: str) -> str:
     """Return ``"hard"`` or ``"soft"`` for one failure string.
 
@@ -390,9 +424,22 @@ class Fitness:
         # leaf with no daylit wall. "urb" (default) = stock hard 0.0, byte-
         # identical to every prior run. "floor"/"compact_ok"/"exempt_circulation"
         # are the three candidate repairs — see quality_uncrinkliness.
+        # homemaker-py-2v1 (§39.8), EXPERIMENTAL: 1.0 (default) is the flat rule,
+        # byte-identical to every prior run. "auto" derives the smallest weight
+        # that makes severing circulation net-negative; a number sets it explicitly.
+        cw = self.conf("connectivity_weight")
+        if cw is None:
+            self._connectivity_weight = 1.0
+        elif isinstance(cw, str) and cw.lower() == "auto":
+            self._connectivity_weight = connectivity_weight_for(
+                float(self.conf("value_inside")),
+                float(self.conf("value_circulation")))
+        else:
+            self._connectivity_weight = float(cw)
         self._crinkliness_mode = str(self.conf("crinkliness_mode") or "urb")
         if self._crinkliness_mode not in (
-                "urb", "floor", "compact_ok", "exempt_circulation"):
+                "urb", "floor", "compact_ok", "exempt_circulation",
+                "usage_daylight"):
             raise ValueError(
                 f"unknown crinkliness_mode: {self._crinkliness_mode!r}")
         # The floored value stays BELOW FAIL_THRESHOLD, so a buried leaf still
@@ -417,6 +464,16 @@ class Fitness:
         req = (self._programme or {}).get(leaf.type)
         return req.usage if req else ""
 
+    def needs_daylight(self, leaf: Node) -> bool:
+        """Does this leaf's declared usage want a window? (homemaker-py-ssz)
+
+        True only for uses a person occupies (``programme.DAYLIGHT_USAGES``).
+        A generic ``C``/``O``/``S`` leaf has no programme entry and so is False,
+        which is the intended reading: a corridor or a covered courtyard is not
+        failing when it has no daylit wall.
+        """
+        return self.usage_of(leaf) in _programme.DAYLIGHT_USAGES
+
     # ------------------------------------------------------------------ #
     # Type superposition + collapse (homemaker-py-9o5)
     # ------------------------------------------------------------------ #
@@ -1161,15 +1218,33 @@ class Fitness:
             # (c) internal corridors are ordinary architecture; stop requiring
             # every circulation leaf to reach daylight.
             return 1.0
+
+        # (b)/(d) one-sided: being MORE compact than target is not a defect the
+        # way over-exposure is. Over-exposure still is one -- a crinkly leaf
+        # costs envelope whatever it is used for -- so this clips the compact
+        # side only, it does not switch the factor off.
+        #
+        # `compact_ok` applies that to every leaf; `usage_daylight` applies it
+        # only where nobody is sitting -- a store, a toilet, plant, a corridor,
+        # a covered courtyard -- and leaves habitable rooms on stock behaviour,
+        # so a windowless bedroom is still the hard failure it should be.
+        one_sided = mode == "compact_ok" or (
+            mode == "usage_daylight" and not self.needs_daylight(leaf))
+
         if not crink:
+            # Zero exposure IS the compact limit (1/crink -> inf), so a
+            # one-sided factor has to score it 1.0. Reaching here and returning
+            # the floor instead was the flaw in the first `compact_ok`: it
+            # announced that compact is not a defect and then punished the most
+            # compact case of all hardest (§38.8).
+            if one_sided:
+                return 1.0
             # (a) floor: keep buried leaves rankable by their other factors
             # instead of collapsing the whole quality product to zero.
-            return self._crinkliness_floor if mode in ("floor", "compact_ok") else 0.0
+            return self._crinkliness_floor if mode == "floor" else 0.0
+
         q = gaussian(1 / crink, 1.0, distance, sigma)
-        if mode == "compact_ok" and 1 / crink > distance:
-            # (b) one-sided: being MORE compact than target is not a defect the
-            # way over-exposure is, so clip to 1.0 on the compact side rather
-            # than decaying symmetrically into a fail.
+        if one_sided and 1 / crink > distance:
             return 1.0
         return max(q, self._crinkliness_floor) if mode in ("floor", "compact_ok") else q
 
@@ -1925,7 +2000,22 @@ class Fitness:
         building_factor = self.evaluate_building(root, tracking)
         value *= building_factor
 
-        # 0.5^n failure penalty (programme-driven mode, not 0.1^n)
+        # 0.5^n failure penalty (programme-driven mode, not 0.1^n).
+        #
+        # homemaker-py-2v1: connectivity failures may carry EXTRA weight. Under
+        # the flat rule every failure costs x0.5, but severing a level's
+        # circulation *gains* value_inside/value_circulation = x6 (the corridor
+        # becomes habitable area when it merges into its sibling), so the
+        # objective was net-positive on destroying the spine — measured x4.06 on
+        # a well-daylit circulation leaf. ``connectivity_weight`` counts each
+        # connectivity fail as w failures; ``"auto"`` derives the smallest w that
+        # makes severing net-negative from the value rates themselves.
+        w = self._connectivity_weight
+        if w != 1.0:
+            n_conn = sum(1 for f in failures if is_connectivity_fail(f))
+            n_other = len(failures) - n_conn
+            value *= 0.5 ** (n_other + w * n_conn)
+        else:
             value *= 0.5 ** len(failures)
 
         score = value / cost if cost != 0.0 else 0.0

src/homemaker_layout/operators.py

@@ -460,6 +460,80 @@ def mutate_bridge_circulation(root: dom.Node, rng: np.random.Generator,
     return _finalise(child), f"bridge_circulation lvl{li}: {names} -> C"
 
 
+def repair_circulation_settled(lvl: dom.Node, reqs, max_bridges: int = 8) -> int:
+    """Reconnect a storey's circulation AFTER the geometry has settled.
+
+    homemaker-py-yql (DESIGN.md §39.9). ``_assign_adjacency_aware`` picks
+    circulation as a CONNECTED dominating set, but it does so against the
+    pre-resize geometry; ``_size_divisions_from_targets`` then moves every wall
+    to hit the programme's area targets and the shared boundaries the dominating
+    set relied on shrink below ``door_width`` or vanish outright. Measured on
+    health-centre: 41 of 49 circulation-to-circulation edges destroyed by the
+    resize, surviving shared walls squeezed to 0.54-1.11 m against a 1.2 m
+    threshold — so only 5% of constructed seeds started connected, against 100%
+    with the resize disabled.
+
+    This is the same alternating-minimisation fix §37.7 applied to room
+    assignment (``_cpsat_relabel_settled``): re-run the step against the
+    geometry that actually resulted. Retypes the cheapest bridging leaves to
+    ``C``, preferring generic outside, then unassigned, and crossing a required
+    room last — the cost model ``mutate_bridge_circulation`` already uses.
+
+    Returns the number of leaves retyped. Idempotent once connected.
+    """
+    import networkx as nx
+
+    from . import geometry as _geo, graph as _graph
+
+    def _cost(node: dom.Node) -> int:
+        if dom.is_circulation(node):
+            return 0
+        if not node.type:
+            return 1
+        if node.type in dom.GENERIC_OUTSIDE:
+            return 0
+        if reqs and node.type in reqs:
+            return 5
+        return 1
+
+    retyped = 0
+    for _ in range(max_bridges):
+        _geo.clear_cache()
+        G = _geo.leaf_graph(lvl, _graph.DOOR_WIDTH)
+        circ = [x for x in G.nodes() if dom.is_circulation(x)]
+        if not circ:
+            return retyped
+        comps = list(nx.connected_components(G.subgraph(circ)))
+        if len(comps) <= 1:
+            return retyped
+        weighted = G.copy()
+        for u, v, data in weighted.edges(data=True):
+            data["bridge_weight"] = (_cost(u) + _cost(v)) / 2.0
+        best_path = None
+        best_weight = None
+        for i in range(len(comps)):
+            for j in range(i + 1, len(comps)):
+                for a in comps[i]:
+                    for b in comps[j]:
+                        try:
+                            path = nx.shortest_path(weighted, a, b,
+                                                    weight="bridge_weight")
+                        except nx.NetworkXNoPath:
+                            continue
+                        w = sum(_cost(x) for x in path[1:-1])
+                        if best_weight is None or w < best_weight:
+                            best_weight, best_path = w, path
+        if not best_path:
+            return retyped
+        middle = [x for x in best_path[1:-1] if not dom.is_circulation(x)]
+        if not middle:
+            return retyped          # components already touch; nothing to retype
+        for leaf in middle:
+            leaf.type = "C"
+            retyped += 1
+    return retyped
+
+
 def _shape_failing(leaf: dom.Node, fit) -> bool:
     """A named-room leaf whose width or proportion factor actually fails
     (``< fitness.FAIL_THRESHOLD``) under ``fit``, the same Gaussian quality
@@ -802,6 +876,129 @@ def _size_divisions_from_targets(lvl: dom.Node, reqs, fmin: float = 0.04,
     geometry.clear_cache()
 
 
+def _circ_components(lvl: dom.Node) -> int:
+    """Number of connected components among this storey's circulation leaves."""
+    import networkx as nx
+
+    from . import geometry as _geo, graph as _graph
+
+    _geo.clear_cache()
+    G = _geo.leaf_graph(lvl, _graph.DOOR_WIDTH)
+    circ = [x for x in G.nodes() if dom.is_circulation(x)]
+    if not circ:
+        return 0
+    return nx.number_connected_components(G.subgraph(circ))
+
+
+def _circ_edges(lvl: dom.Node) -> list[tuple]:
+    """Circulation-to-circulation adjacencies on this storey, as leaf pairs."""
+    from . import geometry as _geo, graph as _graph
+
+    _geo.clear_cache()
+    G = _geo.leaf_graph(lvl, _graph.DOOR_WIDTH)
+    return [(a, b) for a, b in G.edges()
+            if dom.is_circulation(a) and dom.is_circulation(b)]
+
+
+def _circ_edge_absent(lvl: dom.Node, a: dom.Node, b: dom.Node) -> bool:
+    from . import geometry as _geo, graph as _graph
+
+    _geo.clear_cache()
+    G = _geo.leaf_graph(lvl, _graph.DOOR_WIDTH)
+    return not (G.has_node(a) and G.has_node(b) and G.has_edge(a, b))
+
+
+def _size_divisions_preserving_circulation(lvl: dom.Node, reqs,
+                                           max_reverts: int = 12, **kw) -> int:
+    """Resize toward the programme's area targets WITHOUT severing circulation.
+
+    homemaker-py-3z0 (DESIGN.md §39.10). ``_assign_adjacency_aware`` picks
+    circulation as a CONNECTED dominating set, then
+    ``_size_divisions_from_targets`` re-cuts every node — new ratio *and* new
+    rotation — and the shared boundaries the dominating set relied on shrink
+    below ``door_width`` or vanish. Measured (§39.9): fully-connected constructed
+    seeds 1/20, 1/20, 0/20 across the corpus, against 100% with the resize
+    skipped entirely. Both halves of the re-cut do damage, in different
+    proportions per programme — on health-centre it is entirely the ratio, on
+    maple-court mostly the rotation — so a fix has to be able to give back
+    either.
+
+    Rather than rebuild the connection afterwards by retyping rooms to ``C``
+    (measured a net loss — it displaces required rooms at a 3-5 fail cascade
+    each, §39.9), this gives back the *geometry* and keeps the programme intact:
+    snapshot every cut, resize, then greedily revert whichever single cut most
+    reduces the circulation component count until the storey is connected again.
+    Reverting a cut costs only the area-target accuracy of that one subtree, and
+    the inner loop optimises ratios anyway — nothing is displaced and no label
+    changes.
+
+    Returns the number of cuts reverted.
+    """
+    from . import geometry as _geo
+
+    nodes = []
+
+    def _walk(node: dom.Node) -> None:
+        if node.divided:
+            nodes.append(node)
+            _walk(node.left)
+            _walk(node.right)
+
+    _walk(lvl)
+    before = {id(x): (x.rotation, list(x.division) if x.division else None)
+              for x in nodes}
+    _pre_circ_edges = _circ_edges(lvl)
+
+    _size_divisions_from_targets(lvl, reqs, **kw)
+
+    if _circ_components(lvl) <= 1:
+        _geo.clear_cache()
+        return 0
+
+    # Which circulation pairs were adjacent BEFORE the re-cut and are not now?
+    # Those are the connections the resize broke, and the cuts that govern each
+    # are exactly the ones between the two leaves — so revert those, rather than
+    # hunting for a single cut that happens to reduce the component count. A
+    # plain greedy gets stuck: often no ONE revert helps even though two would.
+    def _paths_between(a: dom.Node, b: dom.Node) -> list[dom.Node]:
+        """Divided nodes on the tree path joining two leaves (via their LCA)."""
+        def _chain(x: dom.Node) -> list[dom.Node]:
+            out = []
+            while x is not None:
+                out.append(x)
+                x = x.parent
+            return out
+        ca, cb = _chain(a), _chain(b)
+        common = set(map(id, cb))
+        lca = next((x for x in ca if id(x) in common), None)
+        if lca is None:
+            return []
+        seen, out = set(), []
+        for chain in (ca, cb):
+            for x in chain:
+                if x.divided and id(x) not in seen:
+                    out.append(x)
+                    seen.add(id(x))
+                if x is lca:
+                    break
+        return out
+
+    broken = [(a, b) for a, b in _pre_circ_edges
+              if _circ_edge_absent(lvl, a, b)]
+    reverted = 0
+    for a, b in broken:
+        if _circ_components(lvl) <= 1 or reverted >= max_reverts:
+            break
+        for node in _paths_between(a, b):
+            rot, div = before.get(id(node), (None, None))
+            if div is None or (node.rotation == rot and node.division == div):
+                continue
+            node.rotation, node.division = rot, list(div)
+            reverted += 1
+    _geo.clear_cache()
+    return reverted
+
+
 def _grow_balanced(node: dom.Node, code: str, k: int) -> None:
     """Turn ``node`` (a leaf) into a balanced binary subtree of ``k`` leaves, all
     typed ``code``. Split ratio/rotation are placeholders ([0.5,0.5], rot 0);
@@ -1207,7 +1404,9 @@ def constructive_topology(seed_root: dom.Node, reqs, rng: np.random.Generator,
                           outside_divisor: int = 3,
                           construction_beam_width: int = 1,
                           multi_use: bool = False,
-                          assign_solver: str = "greedy") -> dom.Node:
+                          assign_solver: str = "greedy",
+                          repair_circulation: bool = False,
+                          preserve_circulation: bool = False) -> dom.Node:
     """Build a seed that instantiates every required space by construction.
 
     The §11.0 diagnosis: random divide+retype chains leave required programme
@@ -1312,11 +1511,14 @@ def constructive_topology(seed_root: dom.Node, reqs, rng: np.random.Generator,
             leaf_co = _leaf_colocate_from_plan(lvl, colocate_plan, reqs) if multi_use else {}
             leaf_extra = {lf: reqs[co].size for lf, co in leaf_co.items()
                           if co in reqs and reqs[co].size > 0}
-            _size_divisions_from_targets(
-                lvl, reqs, leaf_mult=_leaf_mult_from_plan(lvl, share_plan),
+            _resize = (_size_divisions_preserving_circulation if preserve_circulation
+                       else _size_divisions_from_targets)
+            _resize(lvl, reqs, leaf_mult=_leaf_mult_from_plan(lvl, share_plan),
                     leaf_extra=leaf_extra)
             if adjacency_aware and assign_solver == "cpsat":
                 _cpsat_relabel_settled(lvl, reqs)
+            if repair_circulation:
+                repair_circulation_settled(lvl, reqs)
 
     return _finalise(child)
 

src/homemaker_layout/programme.py

@@ -104,6 +104,12 @@ TOILET_STRIPS = ("living", "kitchen", "toilet")
 # Sociable rooms keep their MOST central circulation neighbour; terminal rooms
 # and toilets keep their LEAST central one.
 SOCIABLE_USAGES = ("living", "kitchen")
+# Uses a person OCCUPIES, and which therefore want a window. Everything else --
+# stores, toilets, plant, corridors, covered courtyards -- is ordinary buried
+# architecture, and `crinkliness_mode="usage_daylight"` stops the objective
+# demanding daylight for it (homemaker-py-ssz, DESIGN.md §38.8). A generic
+# `C`/`O`/`S` leaf has no programme usage and is exempt for the same reason.
+DAYLIGHT_USAGES = ("living", "kitchen", "bedroom")
 
 
 def validate_codes(codes) -> None:

tests/test_fitness.py

@@ -528,6 +528,93 @@ def test_crinkliness_exempt_circulation_only_exempts_circulation():
     assert f.quality_uncrinkliness(room, None, {}) == 0.0
 
 
+def test_crinkliness_compact_ok_scores_the_buried_limit_as_compact():
+    """Regression (§38.8): a zero-exposure leaf IS the compact limit.
+
+    The first `compact_ok` returned the floor here, i.e. it announced that
+    being compact is not a defect and then punished the most compact case of
+    all hardest -- which is why it measured inert on buried leaves.
+    """
+    f, leaf = _stub_fit("compact_ok", stub=0.0)
+    assert f.quality_uncrinkliness(leaf, None, {}) == 1.0
+
+
+def _usage_fit(mode, stub, code, usage):
+    """Stub Fitness carrying a one-space programme, so `usage_of` resolves."""
+    conf = dict(CONF_DEFAULTS)
+    conf["crinkliness_mode"] = mode
+    conf["spaces"] = {code: {"usage": usage, "size": [4.0, 1.0]}}
+    f = _StubCrink(conf, dict(COST_DEFAULTS))
+    f._stub = stub
+    return f, _leaf(code)
+
+
+@pytest.mark.parametrize("usage", ["toilet", "utility", "none"])
+def test_usage_daylight_exempts_uses_nobody_sits_in(usage):
+    """A buried store or toilet is ordinary architecture, not a failure."""
+    f, leaf = _usage_fit("usage_daylight", 0.0, "x1", usage)
+    assert f.needs_daylight(leaf) is False
+    assert f.quality_uncrinkliness(leaf, None, {}) == 1.0
+
+
+@pytest.mark.parametrize("usage", ["living", "kitchen", "bedroom"])
+def test_usage_daylight_still_fails_a_windowless_habitable_room(usage):
+    """The point of keying on usage: a bedroom with no daylight stays a hard
+    zero, exactly as stock. A mode that rescued this would be deleting the
+    fail category, not fixing the objective."""
+    f, leaf = _usage_fit("usage_daylight", 0.0, "x1", usage)
+    assert f.needs_daylight(leaf) is True
+    assert f.quality_uncrinkliness(leaf, None, {}) == 0.0
+
+
+def test_usage_daylight_exempts_generic_types():
+    """Generic `C`/`S` have no programme entry; a corridor needs no window."""
+    f, _ = _usage_fit("usage_daylight", 0.0, "x1", "living")
+    for code in ("C", "S"):
+        assert f.quality_uncrinkliness(_leaf(code), None, {}) == 1.0
+
+
+def test_usage_daylight_still_punishes_over_exposure():
+    """Exempt from needing daylight is not exempt from envelope cost: the
+    factor is clipped on the compact side only, never switched off."""
+    target = CONF_DEFAULTS["uncrinkliness"][0]
+    f, leaf = _usage_fit("usage_daylight", 1.0 / (target / 2), "x1", "utility")
+    assert f.quality_uncrinkliness(leaf, None, {}) < 1.0
+
+
+def test_usage_daylight_leaves_stock_urb_untouched():
+    """Same tree, mode off -> stock hard zero for every usage."""
+    for usage in ("living", "toilet", "none"):
+        f, leaf = _usage_fit("urb", 0.0, "x1", usage)
+        assert f.quality_uncrinkliness(leaf, None, {}) == 0.0
+
+
 def test_crinkliness_mode_unknown_raises():
     with pytest.raises(ValueError, match="crinkliness_mode"):
         _stub_fit("nonsense")
+
+
+# --------------------------------------------------------------------------- #
+# homemaker-py-2v1 / DESIGN.md §39.8 — connectivity_weight (EXPERIMENTAL, NULL)
+# --------------------------------------------------------------------------- #
+def test_connectivity_weight_defaults_to_flat_rule():
+    """Default must reproduce the flat 0.5^n penalty exactly."""
+    assert Fitness(conf={})._connectivity_weight == 1.0
+
+
+def test_connectivity_weight_auto_is_derived_from_the_value_gap():
+    """Not a magic number: the smallest w making 0.5^w < value_circulation /
+    value_inside, so it tracks the rates if either is retuned."""
+    from homemaker_layout.fitness import connectivity_weight_for
+    assert connectivity_weight_for(300.0, 50.0) == 3.0     # 0.5^3 < 1/6 < 0.5^2
+    assert connectivity_weight_for(100.0, 100.0) == 1.0    # no gap, no extra weight
+    assert connectivity_weight_for(400.0, 50.0) == 3.0     # 1/8 -> exactly 3
+    assert Fitness(conf={"connectivity_weight": "auto"})._connectivity_weight == 3.0
+
+
+def test_is_connectivity_fail_matches_both_strings():
+    from homemaker_layout.fitness import is_connectivity_fail
+    assert is_connectivity_fail("level 0 not connected")
+    assert is_connectivity_fail("1 inaccessible usable space")
+    assert not is_connectivity_fail("0/llr crinkliness")
+    assert not is_connectivity_fail("missing required space: b1")

tests/test_operators.py

@@ -937,3 +937,89 @@ def test_assign_cpsat_beats_greedy_on_a_namespace_clean_programme():
         return total
 
     assert secondary_fails("cpsat") < secondary_fails("greedy")
+
+
+# --------------------------------------------------------------------------- #
+# homemaker-py-yql / DESIGN.md §39.9 — settled-geometry circulation repair
+# --------------------------------------------------------------------------- #
+@pytest.mark.skipif(not HARBOR.is_dir(), reason="harbor-house not available")
+def test_repair_circulation_default_off_reproduces_prior_seeds():
+    """Default off must be byte-identical, like every other experimental flag."""
+    from homemaker_layout import programme
+
+    reqs = programme.load_programme_dir(str(HARBOR))
+    types = sorted(reqs) + ["C", "O"]
+    seed = dom.load(str(HARBOR / "init.dom"))
+    kw = dict(min_storeys=programme.storey_minimum(str(HARBOR)),
+              adjacency_aware=True, proportion_aware=True, circ_divisor=3)
+
+    def sig(**extra):
+        root = operators.constructive_topology(
+            seed, reqs, np.random.default_rng(3), types, **kw, **extra)
+        return tuple(lf.type for lvl in dom.levels(root) for lf in lvl.leaves())
+
+    assert sig() == sig(repair_circulation=False)
+
+
+@pytest.mark.skipif(not HARBOR.is_dir(), reason="harbor-house not available")
+def test_repair_circulation_reconnects_every_storey():
+    """§39.9: the constructed circulation dominating set is connected, but
+    _size_divisions_from_targets then moves every wall and the shared
+    boundaries it relied on drop below door_width. Repairing against the
+    SETTLED geometry restores connectivity — measured 52% -> 100% of levels on
+    harbor-house. (Whether that is a net WIN is a different question: it is
+    not, see §39.9 — it displaces required rooms. Hence default off.)
+    """
+    import networkx as nx
+
+    from homemaker_layout import geometry, graph as graph_mod, programme
+
+    reqs = programme.load_programme_dir(str(HARBOR))
+    types = sorted(reqs) + ["C", "O"]
+    seed = dom.load(str(HARBOR / "init.dom"))
+
+    def levels_connected(repair: bool) -> tuple[int, int]:
+        ok = tot = 0
+        for s in range(6):
+            root = operators.constructive_topology(
+                seed, reqs, np.random.default_rng(s), types,
+                min_storeys=programme.storey_minimum(str(HARBOR)),
+                adjacency_aware=True, proportion_aware=True, circ_divisor=3,
+                repair_circulation=repair)
+            for lvl in dom.levels(root):
+                geometry.clear_cache()
+                G = geometry.leaf_graph(lvl, graph_mod.DOOR_WIDTH)
+                circ = [n for n in G.nodes() if dom.is_circulation(n)]
+                tot += 1
+                if circ and nx.is_connected(G.subgraph(circ)):
+                    ok += 1
+        return ok, tot
+
+    off_ok, off_tot = levels_connected(False)
+    on_ok, on_tot = levels_connected(True)
+    assert on_ok == on_tot, f"repair left {on_tot - on_ok} storeys disconnected"
+    assert on_ok > off_ok, f"repair did not help: {off_ok}/{off_tot} -> {on_ok}/{on_tot}"
+
+
+@pytest.mark.skipif(not HARBOR.is_dir(), reason="harbor-house not available")
+def test_preserve_circulation_default_off_reproduces_prior_seeds():
+    """§39.10 measured NULL, so the default must stay byte-identical."""
+    from homemaker_layout import geometry, programme
+
+    reqs = programme.load_programme_dir(str(HARBOR))
+    types = sorted(reqs) + ["C", "O"]
+    seed = dom.load(str(HARBOR / "init.dom"))
+    kw = dict(min_storeys=programme.storey_minimum(str(HARBOR)),
+              adjacency_aware=True, proportion_aware=True, circ_divisor=3)
+
+    def sig(**extra):
+        geometry.clear_cache()
+        root = operators.constructive_topology(
+            seed, reqs, np.random.default_rng(5), types, **kw, **extra)
+        geometry.clear_cache()
+        return tuple((lf.type, round(geometry.area(lf), 6))
+                     for lvl in dom.levels(root) for lf in lvl.leaves())
+
+    assert sig() == sig(preserve_circulation=False)
+    # ...and it does change something when enabled, or the A/B measured nothing
+    assert sig() != sig(preserve_circulation=True)