fix: resolve chain segment thickness in one place

Issue: #234
User-Visible: yes

demo/smoke_wall_chain_thickness.mjs

@@ -0,0 +1,110 @@
+/**
+ * Issue #234: a chain stores the thickness it was drawn with.
+ *
+ * The defect: "thickness of segment i" was decided by six independent formulas
+ * with three different fallbacks, so a chain drawn at 30 cm could be previewed
+ * at 30 and written as 15. The check below builds a chain whose last segment has
+ * no recorded thickness — the shape a mid-edit toolbar field used to produce —
+ * and then reads three things that used to disagree: the committed partitions,
+ * what the Thickness tool reports for the same stretch, and what a resumed
+ * legacy draft carries.
+ */
+import { launch, checkAll, finish } from './serve.mjs';
+const { page, browser } = await launch();
+
+const res = await page.evaluate(async () => {
+  const out = {};
+  const c = window.__card;
+  const upd = async () => { c._cfgEpoch++; c.requestUpdate(); await c.updateComplete; };
+  const sp = () => c._serverCfg.spaces.find((s) => s.id === c._space);
+
+  c._setMode('plan');
+  c._tool = 'draw';
+  await upd();
+
+  const space = sp();
+  const savedRooms = JSON.parse(JSON.stringify(space.rooms || []));
+  const savedPartitions = JSON.parse(JSON.stringify(space.partitions || []));
+  const savedDrafts = space.room_drafts ? JSON.parse(JSON.stringify(space.room_drafts)) : null;
+  space.rooms = [];
+  space.partitions = [];
+  delete space.room_drafts;
+  await upd();
+
+  const g = c._gridPitch;
+  const pts = [
+    [100, 100],
+    [100 + 6 * g, 100],
+    [100 + 6 * g, 100 + 6 * g],
+    [100 + 12 * g, 100 + 6 * g],
+  ];
+
+  // Two recorded segments at 30 and 25 cm, then a third point whose thickness
+  // is missing: exactly what a field left mid-edit produced before #234.
+  c._drawWallField = '30';
+  await upd();
+  out.fieldAcceptedThirty = c._drawWallCm === 30;
+  c._activeDraftId = null;
+  c._path = [pts[0], pts[1], pts[2], pts[3]];
+  c._draftSegmentCms = [30, 25];
+  c._closingWallCm = null;
+  await upd();
+
+  // Preview and the writer must agree on that third segment.
+  const previewD = (c.shadowRoot || c.renderRoot)
+    ?.querySelector('path.drawwall-preview')?.getAttribute('d') || '';
+  out.previewRendered = previewD.length > 0;
+
+  out.committed = c._finishWallChain();
+  await upd();
+  const stored = (sp().partitions || []).map((p) => p.cm);
+  out.storedThreeSegments = stored.length === 3;
+  out.storedFirstThirty = stored[0] === 30;
+  out.storedSecondTwentyFive = stored[1] === 25;
+  // The gap inherits the previous segment, never the global default.
+  out.gapInheritedPrevious = stored[2] === 25;
+  out.nothingFellBackToFifteen = !stored.includes(15);
+
+  // The Thickness tool reads the same value it stored: the mismatch between
+  // highlight and record is how the defect was noticed in the first place.
+  const mid = (a, b) => [(a[0] + b[0]) / 2, (a[1] + b[1]) / 2];
+  const path = [pts[0], pts[1], pts[2], pts[3]];
+  const reported = [
+    c._wallSourceCmAt(mid(pts[0], pts[1]), path, [30, 25]),
+    c._wallSourceCmAt(mid(pts[1], pts[2]), path, [30, 25]),
+    c._wallSourceCmAt(mid(pts[2], pts[3]), path, [30, 25]),
+  ];
+  out.highlightMatchesStored = reported[0] === stored[0]
+    && reported[1] === stored[1] && reported[2] === stored[2];
+
+  // A draft saved with fewer records than segments (data written before this
+  // fix) resumes with a full vector instead of carrying a hidden 15 cm.
+  space.partitions = [];
+  space.room_drafts = [{
+    id: 'legacy-234',
+    points: pts.map((p) => [p[0] / 1000, p[1] / 1000]),
+    segments: [{ cm: 30 }],
+  }];
+  c._resumeDraftBySpace[c._space] = 'legacy-234';
+  c._path = [];
+  c._draftSegmentCms = [];
+  c._activeDraftId = null;
+  await upd();
+  c._resumeLastDraft();
+  await upd();
+  out.legacyResumedFullVector = c._draftSegmentCms.length === c._path.length - 1;
+  out.legacyGapsInheritedThirty = c._draftSegmentCms.every((cm) => cm === 30);
+
+  c._path = [];
+  c._draftSegmentCms = [];
+  c._activeDraftId = null;
+  delete c._resumeDraftBySpace[c._space];
+  space.rooms = savedRooms;
+  space.partitions = savedPartitions;
+  if (savedDrafts) space.room_drafts = savedDrafts; else delete space.room_drafts;
+  await upd();
+  return out;
+});
+
+checkAll(res);
+await finish(browser);

docs/CHANGELOG.md

@@ -2,6 +2,14 @@
 
 ## Unreleased
 
+- A chain of walls now stores the thickness it was drawn with. A segment whose
+  thickness was not recorded — which happened while the toolbar field was being
+  edited between segments — used to be previewed at the drawn value and saved at
+  15 cm, and the plan only revealed it later when the Thickness tool reported a
+  number nobody had chosen. Preview, both writers and the Thickness highlight now
+  read one resolver, and a missing record inherits the previous segment of the
+  same chain ([#234](https://github.com/Matysh/houseplan-card/issues/234)).
+
 - Wall hatching no longer changes density with the space's grid scale. The same
   15 cm wall used to look different on plans with different `cell_cm` — from a
   dense set of stripes to almost none, a 25× spread. The step is now a distance

docs/CHANGELOG.ru.md

@@ -8,6 +8,14 @@
 
 ## Не выпущено
 
+- Цепочка стен сохраняет ту толщину, которой её нарисовали. Отрезок, толщина
+  которого не была записана — это случалось, если поле толщины правили между
+  отрезками, — показывался с нарисованной толщиной, а сохранялся с 15 см, и
+  расхождение обнаруживалось позже: инструмент «Толщина» подсвечивал значение,
+  которого никто не выбирал. Теперь превью, оба пути записи и подсветка читают
+  один резолвер, а пропуск наследует толщину предыдущего отрезка той же цепочки
+  ([#234](https://github.com/Matysh/houseplan-card/issues/234)).
+
 - Плотность штриховки стен больше не зависит от масштаба пространства. Раньше
   одна и та же стена 15 см выглядела на планах с разным `cell_cm` по-разному —
   от плотной сетки полос до почти пустой полосы, разброс достигал 25 раз.

scripts/mutation-gate.mjs

@@ -40,6 +40,47 @@ import { fileURLToPath } from 'node:url';
 // `find` обязан встречаться в файле ровно один раз: патч, который ложится «куда
 // попало», проверяет не то, что объявлен проверять. Это контролирует --check.
 export const MUTANTS = [
+  {
+    id: 'chain-thickness-falls-back-to-default',
+    guard: 'npx tsc -p tsconfig.test.json && node scripts/fix-test-build.mjs '
+      + '&& node --test --test-name-pattern="chainSegmentCms fills a gap" '
+      + 'test/wall-face-graph.test.mjs',
+    because: 'a segment whose thickness was not recorded must inherit the previous segment of '
+      + 'its own chain — the value the person watched on screen — instead of the global default '
+      + 'that silently replaced 30 cm with 15 cm in the stored plan (#234)',
+    patches: [{
+      file: 'src/wall-face-graph.ts',
+      find: '    const cm = own ?? previous ?? fallbackTail;',
+      replace: '    const cm = own ?? fallbackTail;',
+    }],
+  },
+  {
+    id: 'chain-thickness-preview-diverges',
+    guard: 'npx tsc -p tsconfig.test.json && node scripts/fix-test-build.mjs '
+      + '&& node --test --test-name-pattern="owns no fallback of its own" '
+      + 'test/wall-face-graph.test.mjs',
+    because: 'the preview and every writer must read one resolver; two formulas for one meaning '
+      + 'is what let the editor show 30 cm while the config kept 15 (#234)',
+    patches: [{
+      file: 'src/wall-face-graph.ts',
+      find: '    result.push({ a: [a[0], a[1]], b: [b[0], b[1]], cm: cms[i] });',
+      replace: '    result.push({ a: [a[0], a[1]], b: [b[0], b[1]], '
+        + 'cm: Number.isFinite(cms[i]) && cms[i] >= 0 ? cms[i] : 15 });',
+    }],
+  },
+  {
+    id: 'chain-thickness-length-invariant-dropped',
+    guard: 'npx tsc -p tsconfig.test.json && node scripts/fix-test-build.mjs '
+      + '&& node --test --test-name-pattern="always returns exactly segmentCount" '
+      + 'test/wall-face-graph.test.mjs',
+    because: 'the resolver must return one thickness per segment for any input: the array drifting '
+      + 'shorter than the path is the mechanism that produced the whole defect (#234)',
+    patches: [{
+      file: 'src/wall-face-graph.ts',
+      find: '  for (let i = 0; i < count; i++) {',
+      replace: '  for (let i = 0; i < Math.min(count, (recorded?.length ?? 0)); i++) {',
+    }],
+  },
   {
     id: 'snapn-returns-input-near-node',
     guard: 'npx tsc -p tsconfig.test.json && node scripts/fix-test-build.mjs '

src/houseplan-card.ts

@@ -158,7 +158,7 @@ import {
 } from './plan-snap-overlay';
 import {
   atomizeWallSegments, buildWallFaceGraph, findNewWallFacesInGraphs,
-  normalizeUnifiedWallTool, wallChainSegments,
+  normalizeUnifiedWallTool, wallChainSegments, chainSegmentCms,
   type WallFaceGraph, type WallGraphFace, type WallGraphSourceSegment,
 } from './wall-face-graph';
 import {
@@ -2617,7 +2617,9 @@ class HouseplanCard extends LitElement {
     if (draft) {
       this._activeDraftId = draft.id;
       this._path = draft.points.map((point) => [...point]);
-      this._draftSegmentCms = draft.segments.map((segment) => segment.cm);
+      this._draftSegmentCms = this._adoptDraftCms(
+        this._path, draft.segments.map((segment: any) => segment.cm), draft.id,
+      );
       this._resumeDraftBySpace[this._space] = draft.id;
     } else {
       this._activeDraftId = null;
@@ -6574,7 +6576,11 @@ class HouseplanCard extends LitElement {
       return true;
     }
     const segments = wallChainSegments(
-      this._path, this._draftSegmentCms, DRAW_WALL_DEFAULT_CM,
+      this._path,
+      chainSegmentCms(
+        this._path.length - 1, this._draftSegmentCms,
+        this._drawWallCm, DRAW_WALL_DEFAULT_CM,
+      ),
     );
     const segmentCount = segments.length;
     if ((sp.partitions || []).length + segmentCount > MAX_PARTITIONS) {
@@ -7268,9 +7274,13 @@ class HouseplanCard extends LitElement {
         this._path = endHit.reverse
           ? [...endHit.draft.points].reverse().map((p) => [...p])
           : endHit.draft.points.map((p) => [...p]);
-        this._draftSegmentCms = endHit.reverse
-          ? [...endHit.draft.segments].reverse().map((s) => s.cm)
-          : endHit.draft.segments.map((s) => s.cm);
+        this._draftSegmentCms = this._adoptDraftCms(
+          this._path,
+          endHit.reverse
+            ? [...endHit.draft.segments].reverse().map((s) => s.cm)
+            : endHit.draft.segments.map((s) => s.cm),
+          endHit.draft.id,
+        );
         return;
       }
       this._activeDraftId = null;
@@ -7289,8 +7299,16 @@ class HouseplanCard extends LitElement {
       return;
     }
     if (!this._canAppendRoomDraftPoint()) return;
+    // Точка и толщина её отрезка пишутся вместе (#234). Раньше запись жила в
+    // отдельном методе, который молча выходил при невалидном поле толщины, и
+    // тогда `_draftSegmentCms` становился короче числа отрезков: превью
+    // показывало текущее поле, а запись — 15 см. Инвариант читается прямо
+    // здесь, а не выводится из двух проверок в разных местах.
+    const cm = this._drawWallCm;
+    if (cm == null) { this._showPhysicalRange(100); return; }
     const beforePath = this._path.map((point) => [...point]);
     this._path = [...this._path, pt];
+    this._draftSegmentCms = [...this._draftSegmentCms, cm];
     this._persistActiveDraftSegment();
     this._offerWallFaces(beforePath);
   }
@@ -7395,8 +7413,10 @@ class HouseplanCard extends LitElement {
     sp.room_drafts.push(saved);
     this._activeDraftId = id;
     this._resumeDraftBySpace[this._space] = id;
-    this._draftSegmentCms = persistedSegments.map((s: any) => Number(s.cm));
     this._path = persistedPoints;
+    this._draftSegmentCms = this._adoptDraftCms(
+      persistedPoints, persistedSegments.map((s: any) => Number(s.cm)), id,
+    );
     this._physicalSel = null;
     this._recordGeometry(this._t('history.draft_merge'), before);
     this._saveConfig();
@@ -7406,12 +7426,35 @@ class HouseplanCard extends LitElement {
     }
   }
 
-  /** Persist every completed draft segment immediately. */
+  /**
+   * Thickness array adopted from storage, brought to the length of the path.
+   *
+   * A record written before #234 may be shorter than the path: the resolver
+   * fills the gaps by the same rule the preview and the writers use, so a
+   * resumed draft cannot carry a hidden 15 cm into the next save. Reported to
+   * the console rather than to the user: the person did not cause it and cannot
+   * fix it.
+   */
+  private _adoptDraftCms(path: readonly (readonly number[])[], recorded: readonly (number | null | undefined)[], id?: string): number[] {
+    const count = Math.max(0, path.length - 1);
+    const resolved = chainSegmentCms(count, recorded, this._drawWallCm, DRAW_WALL_DEFAULT_CM);
+    if (recorded.length !== count) {
+      console.debug(
+        `[houseplan] draft ${id ?? '?'}: восстановлено толщин ${count - recorded.length} (#234)`,
+      );
+    }
+    return resolved;
+  }
+
+  /**
+   * Persist every completed draft segment immediately.
+   *
+   * The thickness of the new segment is already recorded by the caller (#234):
+   * this method must not decide whether to record it, or the array and the path
+   * drift apart the moment the toolbar field is mid-edit.
+   */
   private _persistActiveDraftSegment(): void {
     if (this._path.length < 2 || !this._curSpaceCfg) return;
-    const cm = this._drawWallCm;
-    if (cm == null) return;
-    this._draftSegmentCms = [...this._draftSegmentCms, cm];
     const before = this._geometrySnapshot();
     const sp = this._curSpaceCfg as any;
     sp.room_drafts ||= [];
@@ -12383,10 +12426,17 @@ class HouseplanCard extends LitElement {
       return validCm(model.room_drafts.find((item) => item.id === draftId)?.segments[index]?.cm)
         ?? DRAW_WALL_DEFAULT_CM;
     }
+    // Толщина отрезка активной цепочки решается тем же резолвером (#234):
+    // именно это значение подсвечивает инструмент «Толщина», и расхождение с
+    // записью здесь было тем способом, которым дефект и обнаружился.
+    const resolved = chainSegmentCms(
+      Math.max(0, activePath.length - 1), activeCms,
+      this._drawWallCm, DRAW_WALL_DEFAULT_CM,
+    );
     for (let i = 0; i + 1 < activePath.length; i++) {
       const a = activePath[i], b = activePath[i + 1];
       if (distToSegment(point, [a[0], a[1], b[0], b[1]]) <= epsilon) {
-        return validCm(activeCms[i]) ?? DRAW_WALL_DEFAULT_CM;
+        return resolved[i] ?? DRAW_WALL_DEFAULT_CM;
       }
     }
     return DRAW_WALL_DEFAULT_CM;
@@ -12441,7 +12491,11 @@ class HouseplanCard extends LitElement {
     const partitions: Array<{ a: number[]; b: number[]; cm: number }> = [];
     if (!accepted.length) {
       partitions.push(...wallChainSegments(
-        batch.activePath, batch.activeCms, DRAW_WALL_DEFAULT_CM,
+        batch.activePath,
+        chainSegmentCms(
+          batch.activePath.length - 1, batch.activeCms,
+          this._drawWallCm, DRAW_WALL_DEFAULT_CM,
+        ),
       ));
     } else {
       const consumed = new Set(accepted.flatMap((decision) => decision.candidate.atomKeys));
@@ -12656,8 +12710,12 @@ class HouseplanCard extends LitElement {
     // Draw-session wall thickness: apply to new edges only; keep neighbour cm
     // on shared stretches. Split naming does not use the Draw field.
     if (!wasSplit) {
-      const edgeCms = [...this._draftSegmentCms, this._closingWallCm || this._drawWallCm || DRAW_WALL_DEFAULT_CM];
-      const cm = edgeCms[0] || this._drawWallCm;
+      const edgeCms = chainSegmentCms(
+        verts.length,
+        [...this._draftSegmentCms, this._closingWallCm ?? undefined],
+        this._drawWallCm, DRAW_WALL_DEFAULT_CM,
+      );
+      const cm = edgeCms[0];
       if (cm != null) {
         this._cfgEpoch++; // the new room must be in the model before keying
         const openCuts = this._openCuts();
@@ -12681,7 +12739,7 @@ class HouseplanCard extends LitElement {
             return distToSegment(mid, [a[0], a[1], b[0], b[1]]) <= this._gridPitch * 0.02;
           });
           if (source >= 0) next = setWallThickness(
-            next, iv.a, iv.b, edgeCms[source] || cm,
+            next, iv.a, iv.b, edgeCms[source],
             this._wallKeyPitch, NORM_W,
           );
         }
@@ -12759,7 +12817,9 @@ class HouseplanCard extends LitElement {
     if (!draft) { delete this._resumeDraftBySpace[this._space]; return; }
     this._activeDraftId = id;
     this._path = draft.points.map((p) => [...p]);
-    this._draftSegmentCms = draft.segments.map((s) => s.cm);
+    this._draftSegmentCms = this._adoptDraftCms(
+      this._path, draft.segments.map((s: any) => s.cm), draft.id,
+    );
     this._clearPlanSnapHover();
   }
 
@@ -13029,8 +13089,14 @@ class HouseplanCard extends LitElement {
       return;
     }
     const before = this._geometrySnapshot();
-    const cms = [...this._draftSegmentCms,
-      this._closingWallCm || this._drawWallCm || DRAW_WALL_DEFAULT_CM];
+    // Замкнутый контур: отрезков столько же, сколько вершин, и последний —
+    // закрывающий. Его известное значение подаётся резолверу как запись, всё
+    // остальное решает единое правило (#234).
+    const cms = chainSegmentCms(
+      verts.length,
+      [...this._draftSegmentCms, this._closingWallCm ?? undefined],
+      this._drawWallCm, DRAW_WALL_DEFAULT_CM,
+    );
     sp.partitions ||= [];
     const seed = Date.now().toString(36);
     for (let i = 0; i < verts.length; i++) {
@@ -13039,7 +13105,7 @@ class HouseplanCard extends LitElement {
         id: `partition-${seed}-${i}`,
         a: [a[0] / NORM_W, a[1] / NORM_W],
         b: [b[0] / NORM_W, b[1] / NORM_W],
-        cm: cms[i] || DRAW_WALL_DEFAULT_CM,
+        cm: cms[i],
       });
     }
     if (this._activeDraftId && Array.isArray(sp.room_drafts)) {
@@ -18544,15 +18610,17 @@ class HouseplanCard extends LitElement {
       if (this._cursorPt) return [...path, this._cursorPt];
       return path.length >= 2 ? path : null;
     })();
+    // Превью берёт толщины из того же резолвера, что и запись (#234). Раньше
+    // здесь была вторая формула, и расходились они ровно на пропуске: на экране
+    // текущее поле, в конфиге — 15 см.
     const previewHalfDepths = previewPts
-      ? previewPts.slice(0, -1).map((_, i) => {
-          const cm = Number(this._draftSegmentCms[i]) > 0
-            ? Number(this._draftSegmentCms[i])
-            : this._contourClosed && i === previewPts.length - 2
-              ? (this._closingWallCm || drawCm || DRAW_WALL_DEFAULT_CM)
-              : (drawCm || DRAW_WALL_DEFAULT_CM);
-          return wallCmToUnits(cm, this._cellCm, this._gridPitch) / 2;
-        })
+      ? chainSegmentCms(
+          previewPts.length - 1,
+          this._contourClosed
+            ? [...this._draftSegmentCms, this._closingWallCm ?? undefined]
+            : this._draftSegmentCms,
+          drawCm, DRAW_WALL_DEFAULT_CM,
+        ).map((cm) => wallCmToUnits(cm, this._cellCm, this._gridPitch) / 2)
       : [];
     const previewD = previewPts
       ? drawWallPreviewD(

src/wall-face-graph.ts

@@ -55,10 +55,60 @@ export function normalizeUnifiedWallTool(value: unknown): unknown {
 }
 
 /** Immutable open-chain projection used by explicit finish and full rejection. */
+/**
+ * Thickness of every segment in a chain — the single answer to that question.
+ *
+ * Issue #234: five call sites decided it independently and disagreed in three
+ * different ways. The preview filled a gap with the toolbar field, the two
+ * partition writers with a hard-coded 15 cm, the room writer with the first
+ * edge's value. So a chain drawn at 30 cm was shown at 30 and stored at 15, and
+ * the owner discovered it much later by hovering a wall. Two formulas for one
+ * meaning always drift; there is exactly one here now.
+ *
+ * A missing record inherits the previous segment of the same chain, then the
+ * toolbar field, then the default (owner's decision 2026-08-21): that is what
+ * the person saw on screen while drawing, and a global default is not.
+ *
+ * Strictly positive is the validity boundary. The previous `wallChainSegments`
+ * accepted a recorded zero, which cannot be drawn through the UI (1..100 cm,
+ * `docs/WALL-THICKNESS.md`) but can sit in an old draft.
+ */
+export function chainSegmentCms(
+  segmentCount: number,
+  recorded: readonly (number | null | undefined)[] | null | undefined,
+  activeCm: number | null | undefined,
+  defaultCm: number,
+): number[] {
+  const count = Number.isFinite(segmentCount) && segmentCount > 0
+    ? Math.floor(segmentCount) : 0;
+  const valid = (value: unknown): number | null =>
+    typeof value === 'number' && Number.isFinite(value) && value > 0 ? value : null;
+  // `defaultCm` — ответственность вызывающего: он передаёт
+  // DRAW_WALL_DEFAULT_CM. Константа сюда не импортируется намеренно — этот
+  // модуль не зависит ни от чего, и второе место, где живёт число 15, было бы
+  // ровно тем дублированием, которое задача и убирает. Невалидный default —
+  // дефект вызывающего, поэтому он приводится к минимальной допустимой
+  // толщине (1 см, docs/WALL-THICKNESS.md), а не к выдуманному значению.
+  const fallbackTail = valid(activeCm) ?? valid(defaultCm) ?? 1;
+  const out: number[] = [];
+  let previous: number | null = null;
+  for (let i = 0; i < count; i++) {
+    const own = valid(recorded?.[i]);
+    const cm = own ?? previous ?? fallbackTail;
+    out.push(cm);
+    previous = cm;
+  }
+  return out;
+}
+
+/**
+ * Drawable segments of a chain. Thickness arrives already resolved (#234): this
+ * function no longer owns a fallback of its own, because owning one is how the
+ * disagreement started.
+ */
 export function wallChainSegments(
   path: readonly (readonly number[])[],
   cms: readonly number[],
-  defaultCm: number,
 ): WallChainSegment[] {
   const result: WallChainSegment[] = [];
   for (let i = 0; i + 1 < path.length; i++) {
@@ -66,8 +116,9 @@ export function wallChainSegments(
     const b = path[i + 1];
     if (!finitePoint(a) || !finitePoint(b)
         || Math.hypot(b[0] - a[0], b[1] - a[1]) <= Number.EPSILON) continue;
-    const cm = Number.isFinite(cms[i]) && cms[i] >= 0 ? cms[i] : defaultCm;
-    result.push({ a: [a[0], a[1]], b: [b[0], b[1]], cm });
+    // The resolver guarantees a positive number per index; a caller that skips
+    // it is a defect, so the value is used as given rather than re-defaulted.
+    result.push({ a: [a[0], a[1]], b: [b[0], b[1]], cm: cms[i] });
   }
   return result;
 }

test/wall-face-graph.test.mjs

@@ -7,6 +7,7 @@ import {
   findNewWallFacesInGraphs,
   normalizeUnifiedWallTool,
   wallChainSegments,
+  chainSegmentCms,
 } from '../test-build/wall-face-graph.js';
 
 const edge = (key, a, b) => ({ key, a, b });
@@ -24,14 +25,76 @@ test('legacy Partition token becomes Walls without mutating other tools', () =>
 });
 
 test('open chain converts endpoints and per-segment thickness without mutation', () => {
+  // Толщины приходят уже разрешёнными (#234): своего fallback у функции нет.
   const path = [[0, 0], [100, 0], [100, 50]];
   const before = JSON.stringify(path);
-  assert.deepEqual(wallChainSegments(path, [0, 25], 15), [
-    { a: [0, 0], b: [100, 0], cm: 0 },
+  assert.deepEqual(wallChainSegments(path, [30, 25]), [
+    { a: [0, 0], b: [100, 0], cm: 30 },
     { a: [100, 0], b: [100, 50], cm: 25 },
   ]);
   assert.equal(JSON.stringify(path), before);
-  assert.deepEqual(wallChainSegments([[0, 0]], [], 15), []);
+  assert.deepEqual(wallChainSegments([[0, 0]], []), []);
+});
+
+test('chainSegmentCms fills a gap from the previous segment, then the field (#234)', () => {
+  // Симптом задачи: цепочка нарисована 30 см, запись последнего отрезка
+  // потеряна. Раньше запись давала 15, превью — 30; теперь ответ один.
+  assert.deepEqual(chainSegmentCms(3, [30, 30], 30, 15), [30, 30, 30]);
+  // Дырка в середине наследует предыдущий, а не следующий и не дефолт.
+  assert.deepEqual(chainSegmentCms(4, [30, undefined, 20], 12, 15), [30, 30, 20, 20]);
+  // Нет ни одной записи — текущее поле.
+  assert.deepEqual(chainSegmentCms(2, [], 22, 15), [22, 22]);
+  // Нет и поля — дефолт вызывающего.
+  assert.deepEqual(chainSegmentCms(2, [], null, 15), [15, 15]);
+});
+
+test('chainSegmentCms treats only strictly positive records as valid (#234)', () => {
+  // Прежняя wallChainSegments считала записанный 0 валидным; через UI ноль
+  // недостижим (1..100 см), но в старом черновике лежать может.
+  assert.deepEqual(chainSegmentCms(3, [0, 30, 0], 25, 15), [25, 30, 30]);
+  assert.deepEqual(chainSegmentCms(4, [NaN, -5, null, 'x'], 18, 15), [18, 18, 18, 18]);
+  assert.deepEqual(chainSegmentCms(2, [Infinity, 40], 18, 15), [18, 40]);
+});
+
+test('chainSegmentCms always returns exactly segmentCount positive numbers (#234)', () => {
+  // Инвариант: длина результата равна числу отрезков при любом входе — именно
+  // его отсутствие и позволяло массиву разъехаться с путём.
+  for (const count of [0, 1, 5]) {
+    for (const recorded of [[], [30], [30, 30, 30, 30, 30, 30, 30], [null, 0, NaN]]) {
+      const out = chainSegmentCms(count, recorded, 20, 15);
+      assert.equal(out.length, count);
+      assert.ok(out.every((cm) => typeof cm === 'number' && cm > 0), JSON.stringify(out));
+    }
+  }
+  // Мусор в самих аргументах длины и дефолта не роняет резолвер.
+  assert.deepEqual(chainSegmentCms(-1, [30], 20, 15), []);
+  assert.deepEqual(chainSegmentCms(2, [30], null, NaN), [30, 30]);
+  assert.deepEqual(chainSegmentCms(2, null, null, null), [1, 1]);
+});
+
+test('wallChainSegments owns no fallback of its own (#234)', () => {
+  // Свойство, а не курьёз: единственный источник значения — резолвер. Если у
+  // этой функции появится собственный дефолт, вернётся ровно та ситуация, из
+  // которой выросла задача — две формулы для одного смысла. Поэтому пропуск
+  // здесь обязан остаться пропуском, а не превратиться в 15 см.
+  const path = [[0, 0], [100, 0], [100, 50]];
+  const out = wallChainSegments(path, [30]);
+  assert.equal(out.length, 2);
+  assert.equal(out[0].cm, 30);
+  assert.equal(out[1].cm, undefined);
+});
+
+test('the preview and the writers cannot disagree, because the source is one (#234)', () => {
+  // Это ядро задачи, поэтому проверяется как свойство, а не как пример:
+  // вектор для превью и вектор для записи строятся одним вызовом.
+  const path = [[0, 0], [100, 0], [100, 60], [0, 60]];
+  const recorded = [30, 30];
+  const field = 30;
+  const resolved = chainSegmentCms(path.length - 1, recorded, field, 15);
+  const written = wallChainSegments(path, resolved).map((segment) => segment.cm);
+  assert.deepEqual(written, resolved);
+  // И то, что раньше расходилось: последний отрезок больше не 15.
+  assert.equal(written[written.length - 1], 30);
 });
 
 test('atomizes endpoint, T, proper X and collinear overlap with provenance', () => {