Re-verify 1ph: the iio bug could never have touched it

d86 asked for the rigorous version of 35's spot-check -- check out the
codebase at the 1ph commit, backport the iio stale-leaf-share fix, re-run
the historical seed sets.

One constraint had to be worked around: this repository's history begins
2026-07-30, six days AFTER the 1ph commit (2026-07-24), so that checkout
does not exist here. Closest reachable stand-in is 391f510 (2026-07-30), a
genuine ancestor of the iio fix and therefore pre-iio, carrying that era's
examples/ and objective. Measured there, not at the true 1ph commit, and
that is a real limitation of the reproduction.

Protocol as published: programme-house, budget 3000, 4 workers, seeds 1-20,
ON vs OFF, both arms finished with --collapse. Run twice over one worktree,
as-is then with the 22-line iio hunk applied.

                            OFF    ON     W/L/T    mean diff  t(df=19)
  published 1ph             7.95   7.10   11/6/3   +0.85      2.38
  pre-iio 391f510           8.05   7.10   11/6/3   +0.95      2.59
  same + iio fix            8.05   7.10   11/6/3   +0.95      2.59

The published verdict reproduces, and the iio fix changes nothing: 0 of 40
(seed, arm) cells differ, per-seed counts equal cell by cell.

It could not have been otherwise. The bug needs a leaf carrying a STALE
share/share_type, and leaf-sharing only stamps a share where a code has
count > 1 -- programme-house declares count: 1 for all six codes. Over 8
constructed seeds at that commit, programme-house had share_type set on 0
of 56 leaves; harbor-house on 24 of 128. _collapse_value reads
leaf.share_type, so the bug is structurally unreachable on the 1ph
protocol. That is why 35 saw 2/3 harbor seeds diverge by 5-8 fails while
programme-house at N=20 moves not one cell: harbor has codes at counts 10,
6 and 5.

20's retroactive caveat is discharged for the 1ph section and stays live
for harbor-house/qpk, where shares exist and divergence was measured.

Kept experiments/rerun_1ph_protocol.sh and both result TSVs.

Closes homemaker-py-d86.

Lint at parity (46); tests 384 passed, 0 failed.

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

DESIGN.md

@@ -2784,6 +2784,13 @@ is real per-seed noise (not a directional bias) that does not appear to overturn
 verdict above, but the exact historical per-seed numbers quoted in this section were not re-measured
 under the fix. See §35 for the mechanism and what was (and wasn't) re-confirmed.
 
+**Caveat DISCHARGED for this section (`homemaker-py-d86`, §38.18).** The 1ph protocol has now been
+re-run at N=20 on a pre-iio commit with and without the fix backported: all 40 (seed, arm) cells are
+identical, and the reason is structural rather than lucky — programme-house declares `count: 1` for
+every code, so no leaf ever acquires a share and the stale-share bug cannot fire on this programme
+at all. The numbers above stand. The caveat remains live for harbor-house/qpk, where shares do exist
+and §35 measured real divergence.
+
 ## 21. Insert/relocate-circulation repair operator (`homemaker-py-8sh`) — DONE (mixed, kept off)
 
 **Motivation.** qi6's remaining candidate (§18): mechanism (a), an explicit search-time
@@ -5778,6 +5785,59 @@ over 2/3/4 workers, asserting each is internally stable and deliberately not
 asserting they agree with each other) and
 `test_scoring_a_frozen_design_is_deterministic`.
 
+### 38.18 The 1ph verdict re-verified: the iio bug could never have touched it (`homemaker-py-d86`)
+
+`d86` asked for the rigorous version of §35's spot-check: take the codebase at the
+`1ph` commit, backport the `iio` stale-leaf-share fix, and re-run the actual
+historical seed sets to see whether the published verdict would have changed.
+
+**One constraint had to be worked around.** This repository's history begins
+**2026-07-30**, six days *after* the 1ph commit (2026-07-24) — the historical
+checkout the issue asks for does not exist here. The closest reachable stand-in
+is `391f510` (2026-07-30), which is a genuine ancestor of the iio fix
+(`929be5b`, 2026-08-01) and therefore pre-iio, and which carries that era's
+`examples/` and objective. Everything below is measured there, not at the true
+1ph commit, and that is a real limitation of the reproduction.
+
+**Protocol as published:** programme-house `init.dom`, budget 3000, 4 workers,
+seeds 1–20, ON vs OFF, both arms finished with `--collapse`. Run twice over the
+same worktree — once as-is, once with the 22-line `iio` `fitness.py` hunk applied.
+
+| codebase | OFF | ON | W/L/T | mean diff | t (df=19) |
+|---|---|---|---|---|---|
+| published 1ph (2026-07-24) | 7.95 | 7.10 | 11/6/3 | +0.85 | 2.38 |
+| pre-iio `391f510` | **8.05** | **7.10** | **11/6/3** | **+0.95** | **2.59** |
+| the same, + iio fix backported | 8.05 | 7.10 | 11/6/3 | +0.95 | 2.59 |
+
+Two results:
+
+1. **The published verdict reproduces.** ON beats OFF, significant at N=20, with
+   a win/loss/tie split identical to the published 11/6/3.
+2. **The iio fix changes nothing — 0 of 40 (seed, arm) cells differ.** Not a
+   coincidence of means: the per-seed fail counts are equal cell by cell.
+
+**And it could not have been otherwise.** The iio bug needs a leaf carrying a
+*stale* `share`/`share_type` — leftover multiplicity from a code the leaf has
+since been retyped away from. Leaf-sharing only ever stamps a share when a code
+has `count > 1`, and **programme-house declares `count: 1` for all six of its
+codes**. Measured directly over 8 constructed seeds at that commit:
+
+| programme | leaves | `share > 1` | `share_type` set |
+|---|---|---|---|
+| programme-house | 56 | **0** | **0** |
+| harbor-house | 128 | 24 | 24 |
+
+`_collapse_value` reads `leaf.share_type`; on programme-house it is never set,
+so the bug is **structurally unreachable on the 1ph protocol**. That is why §35
+saw 2 of 3 harbor seeds diverge by 5–8 fails while programme-house at N=20 moves
+not one cell — harbor has codes at counts 10, 6 and 5.
+
+§20's retroactive caveat is therefore **discharged for the 1ph section** and
+stays live for harbor-house/qpk, where shares exist and the divergence was
+measured. Worth noting for future archaeology: "was this measurement affected by
+bug X" is often answerable from the programme's structure without re-running
+anything.
+
 ## 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

experiments/rerun_1ph_protocol.sh

@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+# Re-run the 1ph protocol (DESIGN.md §20): programme-house init.dom, budget 3000,
+# 4 workers, seeds 1-20, ON vs OFF, BOTH arms finished with --collapse.
+set -u
+W="$1"; TAG="$2"; OUT="$3"
+cd "$W/examples/programme-house"
+: > "$OUT"
+for seed in $(seq 1 20); do
+  for arm in on off; do
+    flag=""; [ "$arm" = "off" ] && flag="--no-collapse-insearch"
+    t0=$(date +%s)
+    PYTHONPATH="$W/src" timeout 600 python -m homemaker_layout.evolve init.dom \
+      --budget 3000 --seed "$seed" --workers 4 --collapse $flag \
+      --output "$OUT.$arm.dom" > "$OUT.$arm.log" 2>&1
+    t1=$(date +%s)
+    n=$(PYTHONPATH="$W/src" python - "$OUT.$arm.dom" <<'PY'
+import copy, sys
+from homemaker_layout import dom, fitness
+conf, cost = fitness.load_config(".")
+_, f = fitness.Fitness(conf, cost).score_with_fails(copy.deepcopy(dom.load(sys.argv[1])))
+print(len(f))
+PY
+)
+    echo -e "$TAG\t$seed\t$arm\t$n\t$((t1-t0))" >> "$OUT"
+  done
+done

experiments/results/d86_1ph_iiofix.tsv

@@ -0,0 +1,40 @@
+iiofix	1	on	5	8
+iiofix	1	off	8	6
+iiofix	2	on	7	8
+iiofix	2	off	8	6
+iiofix	3	on	9	8
+iiofix	3	off	8	6
+iiofix	4	on	9	7
+iiofix	4	off	11	5
+iiofix	5	on	9	8
+iiofix	5	off	8	7
+iiofix	6	on	8	7
+iiofix	6	off	11	5
+iiofix	7	on	9	8
+iiofix	7	off	11	6
+iiofix	8	on	8	8
+iiofix	8	off	7	7
+iiofix	9	on	6	7
+iiofix	9	off	9	6
+iiofix	10	on	4	8
+iiofix	10	off	7	7
+iiofix	11	on	5	7
+iiofix	11	off	5	6
+iiofix	12	on	7	8
+iiofix	12	off	6	7
+iiofix	13	on	6	7
+iiofix	13	off	9	6
+iiofix	14	on	8	8
+iiofix	14	off	7	6
+iiofix	15	on	6	8
+iiofix	15	off	8	6
+iiofix	16	on	8	7
+iiofix	16	off	8	6
+iiofix	17	on	6	7
+iiofix	17	off	8	6
+iiofix	18	on	7	7
+iiofix	18	off	8	6
+iiofix	19	on	8	7
+iiofix	19	off	7	6
+iiofix	20	on	7	7
+iiofix	20	off	7	6

experiments/results/d86_1ph_preiio.tsv

@@ -0,0 +1,40 @@
+preiio	1	on	5	8
+preiio	1	off	8	6
+preiio	2	on	7	7
+preiio	2	off	8	6
+preiio	3	on	9	7
+preiio	3	off	8	7
+preiio	4	on	9	8
+preiio	4	off	11	6
+preiio	5	on	9	8
+preiio	5	off	8	7
+preiio	6	on	8	8
+preiio	6	off	11	6
+preiio	7	on	9	7
+preiio	7	off	11	6
+preiio	8	on	8	7
+preiio	8	off	7	6
+preiio	9	on	6	8
+preiio	9	off	9	5
+preiio	10	on	4	7
+preiio	10	off	7	7
+preiio	11	on	5	7
+preiio	11	off	5	6
+preiio	12	on	7	8
+preiio	12	off	6	7
+preiio	13	on	6	8
+preiio	13	off	9	6
+preiio	14	on	8	8
+preiio	14	off	7	6
+preiio	15	on	6	8
+preiio	15	off	8	6
+preiio	16	on	8	7
+preiio	16	off	8	5
+preiio	17	on	6	7
+preiio	17	off	8	6
+preiio	18	on	7	7
+preiio	18	off	8	5
+preiio	19	on	8	7
+preiio	19	off	7	5
+preiio	20	on	7	7
+preiio	20	off	7	6