diff --git a/demo/golden/matrix.mjs b/demo/golden/matrix.mjs
index 24a64a73..46d8e749 100644
--- a/demo/golden/matrix.mjs
+++ b/demo/golden/matrix.mjs
@@ -1339,6 +1339,14 @@ export const GOLDEN_SCENARIOS = Object.freeze([
     // must keep the same smooth circular rim; the wall still clips its side.
     zoom: 4, zoomCenter: [500, 380],
     ledStripOverride: { points: [[0.43, 0.35], [0.535, 0.35]] }, ...stage },
+  { id: 'led-strip-rectangle-door-zoom-light', fixture: 'visual', ledStrips: true, space: 'golden-led',
+    mode: 'view', fillMode: 'none', language: 'en', theme: 'light', viewport: { width: 1000, height: 760 },
+    // #787: four stored corners must remain four straight visible sides. The
+    // right side crosses led-door: the opening is optically open, but neither
+    // the stripe nor its emitter line may step back to the wall axis there.
+    zoom: 1.15, zoomCenter: [310, 350],
+    ledStripOverride: { points: [[0.068333, 0.088333], [0.551667, 0.088333],
+      [0.551667, 0.611667], [0.068333, 0.611667], [0.068333, 0.088333]] }, ...stage },
   { id: 'led-strip-off-light', fixture: 'visual', ledStrips: true, space: 'golden-led',
     mode: 'view', fillMode: 'none', stateOverrides: LED_STRIPS_OFF, language: 'en', theme: 'light',
     viewport: { width: 1000, height: 760 }, ...stage },
diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index a82f57ef..d7d37c0c 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -2,6 +2,11 @@
 
 ## Unreleased
 
+- Fixed rectangular LED strips on wall faces: corners remain exact miters and
+  doors, gates and passages no longer pull the stripe or its Glow emitters
+  back to the wall axis, causing steps and bends
+  ([#787](https://github.com/Matysh/houseplan-card/issues/787)).
+
 - Fixed LED-strip Glow end caps so free ends stay smoothly round at high zoom
   instead of exposing polygon facets depending on nearby walls
   ([#786](https://github.com/Matysh/houseplan-card/issues/786)).
diff --git a/docs/CHANGELOG.ru.md b/docs/CHANGELOG.ru.md
index 261e1223..6b88511c 100755
--- a/docs/CHANGELOG.ru.md
+++ b/docs/CHANGELOG.ru.md
@@ -8,6 +8,11 @@
 
 ## Не выпущено
 
+- Исправлены прямоугольные LED-ленты на гранях стен: углы теперь остаются
+  точными стыками, а двери, ворота и проходы больше не возвращают ленту и
+  излучатели Glow на ось стены, создавая ступеньки и изгибы
+  ([#787](https://github.com/Matysh/houseplan-card/issues/787)).
+
 - Исправлены торцы Glow у LED-лент: свободные концы остаются
   плавно круглыми при сильном приближении и больше не показывают грани
   многоугольника в зависимости от соседних стен
diff --git a/docs/LIGHT.md b/docs/LIGHT.md
index 4bfa7ff0..43b55cbf 100644
--- a/docs/LIGHT.md
+++ b/docs/LIGHT.md
@@ -437,6 +437,14 @@ only the geometry differs:
   opening; Dashed zero walls are transparent. Emitters on a thick face sit
   `epsilonGeom` (0.001 cm) outward into free floor; a part buried in a body
   emits nothing; a strip entirely inside a wall has no field.
+- **Wall openings and corners.** A door, gate or passage remains optically
+  open, but an internal gap between two collinear pieces of the same wall face
+  inherits their free-side normal. The visible stripe and its emitters
+  therefore stay on one straight line through the opening. At a genuine turn,
+  safely intersecting shifted sides use that bounded intersection as their
+  single miter; unsafe acute angles retain the short connector. A stored
+  four-corner loop consequently stays a four-corner rectangle without steps
+  at openings or diagonal corner inserts (#787).
 - **Core.** With effective Glow (space `glow_enabled` + room `glow`) the core
   stays white and the colour is the field; without Glow the core takes the
   source colour and there is no field. Off: white core, no field.
diff --git a/docs/design/led-strips/ACCEPTANCE.md b/docs/design/led-strips/ACCEPTANCE.md
index 587d0420..4ed6dce1 100644
--- a/docs/design/led-strips/ACCEPTANCE.md
+++ b/docs/design/led-strips/ACCEPTANCE.md
@@ -42,7 +42,7 @@ behaviours, not of positions.
 | Off: white core, no field, both themes | stripe state `off` | smoke `smoke_led_strip_glow.mjs`, `led-strip-off-light` |
 | On with Glow: white core + coloured field; without Glow: core in the source colour, no field | `ledStripView` + `resolveGlowAppearance` | smoke `smoke_led_strip_glow.mjs` |
 | Glow is the space/room switch, independent of `fill_mode` | `glowFor(room)` | `lighting-led-strip-glow-dark` uses `fill_mode: none` |
-| Per-piece offset: t/2 on a thick face into free floor, 0 on free floor and zero walls; continuous transition | `visibleStripPath` | unit `test/led-strip-geometry.test.mjs` (AC8) |
+| Per-piece offset: t/2 on a thick face into free floor, 0 on free floor and zero walls; continuous transition; a collinear door gap keeps the flanking face normal and shifted sides meet at one bounded miter | `stripPieces` + `visibleStripPath` | unit `test/led-strip-geometry.test.mjs` (AC8, #787); golden `led-strip-rectangle-door-zoom-light` |
 | Field 30 cm by default, own `glow_radius_cm` wins; round free ends; no seams, bands, missing free runs or doubled brightness at corners/closure | `ledFrame`, one continuous path through exact circular free fans and obstacle-clipped visibility fans in `led-strip-field` | unit `test/led-strip-runtime.test.mjs`; golden `led-strip-long-zigzag-glow-light`, `led-strip-endcaps-zoom-light`; reference pair |
 | Shared `glowAlpha` / `GLOW_FALLOFF` / `GLOW_FADE_MS` | field bands from `falloffAt` | unit `test/led-strip-runtime.test.mjs` |
 | Field under icons, badges and labels; icons not tinted | glow layer below the device layer | reference pair (designer tinting deliberately not reproduced) |
diff --git a/src/led-strip-geometry.ts b/src/led-strip-geometry.ts
index 33ca30f7..11651ce7 100755
--- a/src/led-strip-geometry.ts
+++ b/src/led-strip-geometry.ts
@@ -176,7 +176,11 @@ function freeNormal(a: Pt, b: Pt, at: Pt, ctx: FaceContext): [number, number] |
   return plusInside ? [-nx + 0, -ny + 0] : [nx + 0, ny + 0];
 }
 
-/** Split every stored segment into face pieces and free pieces (ТЗ §3). */
+/**
+ * Split every stored segment into face pieces and free pieces (ТЗ §3).
+ * An internal opening between collinear pieces of the same body face inherits
+ * their free side: a door is optically open, but it does not bend the strip.
+ */
 export function stripPieces(points: readonly Pt[], ctx: FaceContext | null): StripPiece[] {
   const path = compactPoints(points);
   const pieces: StripPiece[] = [];
@@ -187,6 +191,7 @@ export function stripPieces(points: readonly Pt[], ctx: FaceContext | null): Str
   }
   for (let i = 1; i < path.length; i++) {
     const a = path[i - 1], b = path[i];
+    const local: Array<StripPiece & { matched: boolean }> = [];
     const intervals: Array<[number, number]> = [];
     if (ctx) {
       for (const face of faces) {
@@ -203,21 +208,82 @@ export function stripPieces(points: readonly Pt[], ctx: FaceContext | null): Str
     }
     let cursor = 0;
     for (const [t0, t1] of merged) {
-      if (t0 > cursor) pieces.push({ a: lerp(a, b, cursor), b: lerp(a, b, t0), free: null });
+      if (t0 > cursor) local.push({ a: lerp(a, b, cursor), b: lerp(a, b, t0), free: null, matched: false });
       const pa = lerp(a, b, t0), pb = lerp(a, b, t1);
       const mid = lerp(a, b, (t0 + t1) / 2);
-      pieces.push({ a: pa, b: pb, free: ctx ? freeNormal(a, b, mid, ctx) : null });
+      local.push({ a: pa, b: pb, free: ctx ? freeNormal(a, b, mid, ctx) : null, matched: true });
       cursor = t1;
     }
-    if (cursor < 1) pieces.push({ a: lerp(a, b, cursor), b: [b[0], b[1]], free: null });
+    if (cursor < 1) local.push({ a: lerp(a, b, cursor), b: [b[0], b[1]], free: null, matched: false });
+
+    // A door/gate/passage cuts a gap out of a physical face. The stored strip
+    // still follows one straight wall side through that gap, so keep the free
+    // side selected by the two flanking face pieces. Leading/trailing free
+    // pieces are deliberately not inherited: a strip that actually leaves a
+    // wall must still return to its stored path.
+    for (let j = 1; j + 1 < local.length; j++) {
+      const prev = local[j - 1], gap = local[j], next = local[j + 1];
+      if (gap.matched || !prev.matched || !next.matched || !prev.free || !next.free) continue;
+      if (Math.hypot(prev.free[0] - next.free[0], prev.free[1] - next.free[1]) <= 1e-9) {
+        gap.free = [prev.free[0], prev.free[1]];
+      }
+    }
+    pieces.push(...local.map(({ a: pa, b: pb, free }) => ({ a: pa, b: pb, free })));
   }
   return pieces.filter((piece) => dist(piece.a, piece.b) > 0);
 }
 
+function shiftedLineIntersection(
+  prev: StripPiece, next: StripPiece, offset: number,
+): [number, number] | null {
+  if (!prev.free || !next.free || !same(prev.b, next.a)) return null;
+  const pa: [number, number] = [prev.a[0] + prev.free[0] * offset, prev.a[1] + prev.free[1] * offset];
+  const pb: [number, number] = [prev.b[0] + prev.free[0] * offset, prev.b[1] + prev.free[1] * offset];
+  const qa: [number, number] = [next.a[0] + next.free[0] * offset, next.a[1] + next.free[1] * offset];
+  const qb: [number, number] = [next.b[0] + next.free[0] * offset, next.b[1] + next.free[1] * offset];
+  const r = sub(pb, pa), s = sub(qb, qa);
+  const den = r[0] * s[1] - r[1] * s[0];
+  if (Math.abs(den) <= 1e-12) return null;
+  const qmp = sub(qa, pa);
+  const t = (qmp[0] * s[1] - qmp[1] * s[0]) / den;
+  const hit: [number, number] = [pa[0] + r[0] * t, pa[1] + r[1] * t];
+  // Acute angles can put an infinite-line intersection far away. Keep the
+  // existing short connector there instead of producing a long miter spike.
+  const maxMiter = Math.max(Math.abs(offset) * 4, 1e-9);
+  return dist(hit, pb) <= maxMiter && dist(hit, qa) <= maxMiter ? hit : null;
+}
+
+function redundantCollinear(a: Pt, b: Pt, c: Pt): boolean {
+  const ab = sub(b, a), bc = sub(c, b);
+  const scale = Math.max(1, Math.hypot(...ab) * Math.hypot(...bc));
+  const cross = ab[0] * bc[1] - ab[1] * bc[0];
+  const forward = ab[0] * bc[0] + ab[1] * bc[1];
+  return Math.abs(cross) <= 1e-12 * scale && forward >= -1e-12;
+}
+
+function simplifyVisiblePoints(points: Array<[number, number]>, closed: boolean): Array<[number, number]> {
+  const out = [...points];
+  let changed = true;
+  while (changed && out.length > (closed ? 3 : 2)) {
+    changed = false;
+    const first = closed ? 0 : 1, last = closed ? out.length : out.length - 1;
+    for (let i = first; i < last; i++) {
+      const prev = out[(i - 1 + out.length) % out.length];
+      const next = out[(i + 1) % out.length];
+      if (!redundantCollinear(prev, out[i], next)) continue;
+      out.splice(i, 1);
+      changed = true;
+      break;
+    }
+  }
+  return out;
+}
+
 /**
  * The derived visible path (ТЗ §3): a face piece shifted `offset` along its
- * free normal, a free piece unshifted, consecutive pieces joined by a short
- * connector (drawn with round joins) — no gap, no square patch, no long miter.
+ * free normal, a free piece unshifted. Shifted sides meeting at a real corner
+ * meet at their bounded line intersection; wall/free transitions and unsafe
+ * acute angles retain the short connector — no gap and no long miter spike.
  * Closed strips close through the same rule. Shared by both strokes, the hit
  * path, focus and 2.5D: one derivation, never a stored position.
  */
@@ -226,21 +292,35 @@ export function visibleStripPath(
 ): { points: Array<[number, number]>; closed: boolean } {
   const closed = isClosedStrip(compactPoints(points));
   const pieces = stripPieces(points, ctx);
+  const shifted = pieces.map((piece) => {
+    const shift = piece.free ? [piece.free[0] * offset, piece.free[1] * offset] : [0, 0];
+    return {
+      a: [piece.a[0] + shift[0], piece.a[1] + shift[1]] as [number, number],
+      b: [piece.b[0] + shift[0], piece.b[1] + shift[1]] as [number, number],
+    };
+  });
+  const joins: Array<[number, number] | null> = pieces.map(() => null);
+  for (let i = 0; i + 1 < pieces.length; i++) {
+    joins[i] = shiftedLineIntersection(pieces[i], pieces[i + 1], offset);
+  }
+  if (closed && pieces.length > 1) {
+    joins[pieces.length - 1] = shiftedLineIntersection(pieces[pieces.length - 1], pieces[0], offset);
+  }
   const out: Array<[number, number]> = [];
   const push = (p: [number, number]) => {
     const last = out[out.length - 1];
     if (!last || Math.hypot(last[0] - p[0], last[1] - p[1]) > 1e-12) out.push(p);
   };
-  for (const piece of pieces) {
-    const shift = piece.free ? [piece.free[0] * offset, piece.free[1] * offset] : [0, 0];
-    push([piece.a[0] + shift[0], piece.a[1] + shift[1]]);
-    push([piece.b[0] + shift[0], piece.b[1] + shift[1]]);
+  for (let i = 0; i < pieces.length; i++) {
+    const previousJoin = i > 0 ? joins[i - 1] : closed ? joins[pieces.length - 1] : null;
+    push(previousJoin ?? shifted[i].a);
+    push(joins[i] ?? shifted[i].b);
   }
   if (closed && out.length > 2) {
     const first = out[0], last = out[out.length - 1];
     if (Math.hypot(first[0] - last[0], first[1] - last[1]) <= 1e-12) out.pop();
   }
-  return { points: out, closed };
+  return { points: simplifyVisiblePoints(out, closed), closed };
 }
 
 export function pathD(path: { points: ReadonlyArray<Pt>; closed: boolean }): string {
diff --git a/test/led-strip-geometry.test.mjs b/test/led-strip-geometry.test.mjs
index 291c8a8a..601155a6 100755
--- a/test/led-strip-geometry.test.mjs
+++ b/test/led-strip-geometry.test.mjs
@@ -93,6 +93,40 @@ test('AC8: a closed strip closes through the same rule without a seam point', ()
   assert.deepEqual(path.points, [[2, 3], [6, 3], [6, 6], [2, 6]]);
 });
 
+test('#787: a four-corner strip stays rectangular across a door opening', () => {
+  // Opaque body faces around a door gap y=3..5 on the rectangle's right side.
+  const faces = [
+    { a: [0, 0], b: [10, 0] }, { a: [10, 0], b: [10, 3] },
+    { a: [10, 5], b: [10, 10] }, { a: [10, 10], b: [0, 10] },
+    { a: [0, 10], b: [0, 0] },
+  ];
+  const openingCtx = {
+    faces,
+    inside: ([x, y]) => (y > -1 && y < 0 && x > 0 && x < 10)
+      || (x > 10 && x < 11 && ((y > 0 && y < 3) || (y > 5 && y < 10)))
+      || (y > 10 && y < 11 && x > 0 && x < 10)
+      || (x > -1 && x < 0 && y > 0 && y < 10),
+    epsilon: 1e-5,
+  };
+  const stored = [[0, 0], [10, 0], [10, 10], [0, 10], [0, 0]];
+  const before = JSON.stringify(stored);
+  const right = stripPieces([[10, 0], [10, 10]], openingCtx);
+  assert.equal(right.length, 3, 'the opening remains a separate derived piece');
+  assert.ok(right.every((piece) => JSON.stringify(piece.free) === JSON.stringify([-1, 0])),
+    'the internal opening inherits the same free side from both wall faces');
+
+  assert.deepEqual(visibleStripPath(stored, openingCtx, 0.25), {
+    points: [[0.25, 0.25], [9.75, 0.25], [9.75, 9.75], [0.25, 9.75]],
+    closed: true,
+  }, 'shifted wall sides meet at exact miters without steps or diagonal inserts');
+  assert.equal(JSON.stringify(stored), before, 'the stored four-corner contour is untouched');
+
+  const emitters = emitterSamples([[10, 0], [10, 10]], openingCtx, 0.5);
+  assert.ok(emitters.length > 0);
+  for (const point of emitters) close(point[0], 10 - openingCtx.epsilon, 1e-12,
+    'Glow stays on one side through the optically open doorway');
+});
+
 test('ТЗ §6: emitters sit epsilon outward on a face, cover the length, skip buried parts', () => {
   const onFace = emitterSamples([[2, 1], [8, 1]], ctx, 1);
   assert.equal(onFace.length, 7, 'every vertex plus spacing ≤ 1');