Lane D R22 (v4.0): citizens at pack scale — fitzroy stress PASS + the thin-tail clustering finding (ledger #5)

Against A's pack absorb (3face97, 23 towns / 36 goldens). selfcheck ALL GREEN
161300/161300, synthetic 0x3fa36874 frozen.

FITZROY STRESS: PASS — the sim doesn't notice 2x scale. 160 shops -> 139 seated (21
dropped, counted), 1859 nodes / 2408 edges (biggest of the epoch), 376 active peds,
0 NaN, 0.08 ms/frame, 22 chunk rosters, 454 identity sigs, 103 patronage visits.
A's R21 cluster bias survives the mecca (min 8 shops within 160m). Nothing needed
touching; the citizen field is not a budget risk at any scale this epoch reaches.

THIN TAIL — "does 12 shops still read alive?" ANSWER: only if they CLUSTER. I checked
both 12-shop towns because they disagree, and the disagreement is the finding:
- darwin_real ALIVE: 27m median nearest-neighbour spacing, 7 of 12 shops within 160m of
  the hub, 18 visits (13 hero).
- toowoomba_real DEAD: 388m median spacing (14x) across a 4.6km road network, only 3
  shops within 160m of its own densest point, 1417 patronage checks -> 0 finds, 0 visits.
  Not a shopping town — a road network with occasional shops.
Verified real, not an R20-style sampling error: 9 shops open at 14:00 in BOTH, camera
stood on the town's own densest point. 0 NaN / 0.05 ms/frame either way.

FILED for E/Fable (curation, not code): MIN_TOWN_SHOPS counts shops, but what makes a
town read alive is clustering. A cheap test that separates them: ">=5 shops within 160m
of the densest point" — darwin 7 PASS, toowoomba 3 FAIL. Toowoomba ships in the v4.0
pack today with no main street to walk. Cull or accept as a known thin-tail (it costs
nothing). E/Fable's call — A's venue bias correctly exempts it ("no better candidate").

D->F: citizens at pack scale GREEN, no D-side blocker for v4.0. Toowoomba is curation,
not a citizen defect — the tag isn't gated on it from me.
Carried to v4.x: GIG_RANGE 34m radius vs single-chunk lookup (8.7% chunk-blind).
Last flag before the retro: R20's main-street relocation half remains unowned (fitzroy
13 hero vs 90 texture visits); one call of this harness re-runs it if v4.x wants it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/LANES/LANE_D_NOTES.md

@@ -6,6 +6,71 @@ _rotOnly/head-bone normalize/upgradeStreetPeople). Measurements on the M3 Ultra
 
 ---
 
+## ROUND 22 — v4.0 THE EPOCH CLOSE: citizens at pack scale (ledger #5)
+
+*PROCITY-D, 2026-07-16. The fitzroy stress audit (160 shops — the densest citizen field this epoch) + the
+thin-tail spot-check. Against A's pack absorb (`3face97`, 23 towns / 36 goldens) — `selfcheck` **ALL GREEN
+161300/161300**, synthetic `0x3fa36874` frozen.*
+
+### Fitzroy stress: PASS — the sim doesn't notice
+| metric | fitzroy_real |
+|---|---|
+| shops | 160 → **139 seated** (21 dropped, counted by cause — A's fence at 2× scale) |
+| graph | **1859 nodes / 2408 edges** (biggest of the epoch) |
+| **active peds** | **376** (avg == max — saturated) |
+| **NaN** | **0** |
+| **sim cost** | **0.08 ms/frame** at 376 peds |
+| chunk rosters / identity sigs | 22 / 454 |
+| venues (A's R21 cluster bias) | 3, **min 8 shops within 160 m** ✓ |
+| patronage | 3086 checks, 79.6 % null, **103 visits** |
+| plan gen | 194 ms |
+
+**Nothing needed touching at 2× scale.** Zero NaN, rosters stream, identity signatures accumulate,
+determinism holds, and the sim layer costs **0.08 ms/frame** with 376 active citizens — the citizen field is
+not a budget risk at any scale this epoch reaches. A's cluster bias survives the mecca (min 8 ≥ the ≥3 bar).
+
+### Thin tail: "does 12 shops still read alive?" — **it depends entirely on CLUSTERING, and one pack town fails**
+I spot-checked **both** 12-shop towns rather than one, because they disagree — and the disagreement is the finding:
+
+| | darwin_real — **ALIVE** | toowoomba_real — **DEAD** |
+|---|---|---|
+| shops / road ways | 12 / 341 | 12 / **866** |
+| **median nearest-neighbour spacing** | **27 m** (a real strip) | **388 m** (14×) |
+| shops within 160 m of the hub | **7 of 12** | **3** |
+| median shop → hub | 101 m | **739 m** (max 2117) |
+| densest cluster | 6 neighbours | **2** |
+| min venue neighbours (A's bias) | 6 ✓ | **1** (no better candidate exists) |
+| open at 14:00 | 9 | **9** (hours are NOT the cause) |
+| patronage | 1455 checks, **18 visits** (13 hero) | 1417 checks, **0 finds, 0 visits** |
+| NaN / sim cost | 0 / 0.05 ms | 0 / 0.05 ms |
+
+**Both towns pass `MIN_TOWN_SHOPS`. One has a high street; the other doesn't.** Darwin's 12 shops sit 27 m
+apart with 7 of them on one strip — it reads as a small town with a main street. Toowoomba's 12 sit ~388 m
+apart across a **4.6 km** road network: **1417 patronage checks returned zero finds** and no citizen shopped
+once in the whole soak. It isn't a shopping town — it's a road network with occasional shops. (I verified
+this is real, not my R20-style sampling error: shops are **open**, camera stood on the town's own densest
+point, and that point only has 3 shops within 160 m.)
+
+**→ FILED for E / Fable (curation, not code): the floor measures the wrong thing.** `MIN_TOWN_SHOPS` counts
+shops; what makes a town read alive is whether they **cluster**. A cheap curation test that separates these
+two cleanly: **"≥5 shops within 160 m of the town's densest point"** — darwin 7 PASS, toowoomba 3 FAIL.
+Toowoomba is in the v4.0 pack today and has no main street to walk. Cull it, or accept it as a known
+thin-tail (it costs nothing — 0 NaN, 0.05 ms/frame — it just has nothing to do). **E/Fable's call, not mine**;
+A's venue bias is *correctly* exempting it ("no better candidate"), so this is a pack-curation question.
+
+### Handshakes
+- **D → F (gate):** citizens at pack scale **GREEN**. 23-town pack: fitzroy (160 shops / 376 peds) clean at
+  0 NaN and 0.08 ms/frame, thin tail stable, determinism + rosters + identity hold everywhere. **No D-side
+  blocker for `v4.0`.** The toowoomba item is curation, not a citizen defect — tag isn't gated on it from me.
+- **Carried to v4.x (unchanged):** `GIG_RANGE` 34 m radius vs the single-chunk `_nearestOpenShop` lookup
+  (8.7 % of in-range peds chunk-blind; fix = chunk + 8 neighbours).
+- **Still unowned (last flag before the retro):** R20's *main-street relocation* half — heroes are a
+  0–19 % minority of the densest cluster on the widened towns (fitzroy: 13 hero vs 90 texture visits). E's
+  3× texture cap bounds the ratio town-wide; whether the **hero strip is the densest cluster** was never
+  verified. If it matters for v4.x, it's a one-call re-run of this harness.
+
+---
+
 ## ROUND 21 — v4.0-beta CLOSE: relocation verify (ledger #4)
 
 *PROCITY-D, 2026-07-16. Verifying A's venue cluster-adjacency bias (`110c828`), which Fable assigned from