diff --git a/docs/design/client.md b/docs/design/client.md
index 9725cb9d..b0b94b44 100644
--- a/docs/design/client.md
+++ b/docs/design/client.md
@@ -87,7 +87,7 @@ Findings (2026-09-28): 卫戍协议 levels have no scene bundle (`mapId` null; t
 
 Correction (2026-10-11, GitHub #532; PR #533 by @andrew05060414): the first finding above was made off season and is wrong. While a season runs, the official hot-update list carries **one prebuilt scene per battlefield** — `scenes/activities/act1autochess/level_act1autochess_m01…m07` and `scenes/activities/act2autochess/level_act2autochess_m01…m04` (each with `…/lightingdata.ab` and `…_lighting_settings.ab`; Android versions `25-11-21-15-21-44_ee1197`, `26-03-13-06-11-47_14fb99`, `26-04-13-12-31-42_e9b560`); the lists of 2026-09-13 and 2026-10-08 have none, and no 卫戍协议 level data either. The asset index of those versions (`<hash>.idx`: each bundle's dependencies) gives each scene's art: act1 m01–m07 and act2 m02 / m04 depend on `arts/maps/map_autochesssand` (m05 and act2 m04 also on `map_doss_shore`), act2 m01 on `map_lakegarden` + `map_syracuse_metro`, act2 m03 on `map_kxmr` + `map_lm_center`. **No battlefield scene depends on `arts/maps/map_autochess`** (the metal theme the procedural board below draws; in the current client the 矢量突破 scenes `act3break` use it). A scene holds the logic tiles (`(row,col)#tileKey` at anchor-local (col, row, −height), high ground 0.4), the art under `GraphicHolder` (static parts merged into "Combined Mesh (root: scene)" objects, lightmapped: Shadowmask mode, one directional key light), and three sub-graphics `HIDDEN@1…3` (`MapSubGraphicHolder`) that the game switches on: the left normal field, the right normal field and the boss field — the areas of `layout.js AREAS`.
 
-Official battlefield scenes (`board3d/load.js loadScenePack`, `scene.js setScenePack`, `materials.js sceneMaterial`): when `data/local-assets.json` lists `scene/<stageId>`, the 3D board draws that scene instead of the procedural tiles, cliffs and background plane; the devices, gate / objective boxes, field edges and terrain overlays stay as below. The base part is always drawn; a `HIDDEN@n` part is drawn when its centre lies in one of the built areas. Without the scene (not extracted, a load failure, an unknown `version`) the procedural metal board is drawn as before. Approximations: the official shaders are not reproduced — a lit material is albedo × (the lightmap's baked light + key light · N·L · the baked shadow mask), in linear light; normal, metallic and emission maps, the vertex-colour blend (`_HG_VERTEX_COLOR_BLEND_ON`), the sky box, the map effects (`mapeff_*`) and the post-processing profile are not drawn; `Torappu/Scene/StylizedWater` is the board's water shader in the material's colours; crates cast no shadow on a scene. **[ASSUMED]** `SCENE_LIGHT` (`direct` 0.8, `indirect` 0.4, `ambient` 0.2: tuned by eye against the PRTS screenshot of 战场#06, the official post-processing being unknown) and the RGBM reading of the lightmap pages (`scenes.py decode_rgbm`: Unity's linear-space decode, range 5). Owner decision (2026-10-12): these extracted files belong to the 0.2.5 asset pack and may ship in the full release zip; a lite package or a source install may download and extract them on that machine. Missing extractor dependencies keep the metal board. The repository still never stores the official files.
+Official battlefield scenes (`board3d/load.js loadScenePack`, `scene.js setScenePack`, `materials.js sceneMaterial`): when `data/local-assets.json` lists `scene/<stageId>`, the 3D board draws that scene instead of the procedural tiles, cliffs and background plane; the devices, gate / objective boxes, field edges and terrain overlays stay as below. The base part is always drawn; a `HIDDEN@n` part is drawn when its centre lies in one of the built areas. Chunks of those shown parts that share a material and a lightmap page are one mesh when the area is built (`load.js mergeSceneChunks`); water shares a mesh across pages because its shader has no lightmap. A switched-off part stays out of that mesh. Without the scene (not extracted, a load failure, an unknown `version`) the procedural metal board is drawn as before. Approximations: the official shaders are not reproduced — a lit material is albedo × (the lightmap's baked light + key light · N·L · the baked shadow mask), in linear light; normal, metallic and emission maps, the vertex-colour blend (`_HG_VERTEX_COLOR_BLEND_ON`), the sky box, the map effects (`mapeff_*`) and the post-processing profile are not drawn; `Torappu/Scene/StylizedWater` is the board's water shader in the material's colours; crates cast no shadow on a scene. **[ASSUMED]** `SCENE_LIGHT` (`direct` 0.8, `indirect` 0.4, `ambient` 0.2: tuned by eye against the PRTS screenshot of 战场#06, the official post-processing being unknown) and the RGBM reading of the lightmap pages (`scenes.py decode_rgbm`: Unity's linear-space decode, range 5). Owner decision (2026-10-12): these extracted files belong to the 0.2.5 asset pack and may ship in the full release zip; a lite package or a source install may download and extract them on that machine. Missing extractor dependencies keep the metal board. The repository still never stores the official files.
 
 Target: a **real 3D board layer** rendered with three.js (vendored ESM, no CDN) underneath the existing Pixi layer:
 - Geometry generated from `data/stages.json` like the official builder: LOW tiles = top quads; HIGH tiles = raised blocks with side walls; forbidden/void, fences, gates (red), objective (blue), hand/temp pads, special terrain; UVs mapped onto the official atlas regions (reuse/extend `public/assets/local/map/autochess/tiles.json`); normal + emission + metallic maps; lighting tuned to match official screenshots (key directional light, ambient/hemisphere, soft contact shadows); official background meshes & texture; device meshes (OBJ exported by `tools/local-extract`) with their textures; animated gate/objective effects.
diff --git a/docs/history/0.2.5.md b/docs/history/0.2.5.md
index 9733914d..106c1995 100644
--- a/docs/history/0.2.5.md
+++ b/docs/history/0.2.5.md
@@ -391,7 +391,9 @@ lightmap pages with the baked shadow mask in alpha, albedo textures) to `public/
 `.cache/official-scenes/*`; `tools/local-extract/fetch_scenes.py` downloads the in-season bundles from the official
 CDN (md5-checked against that version's hot-update list). The 3D board draws a stage's scene when the local-art
 manifest lists it (`board3d/load.js loadScenePack`, `scene.js setScenePack`); the procedural metal board stays the
-fallback and still draws the devices, gates, field edges and terrain overlays.
+fallback and still draws the devices, gates, field edges and terrain overlays. Chunks of the parts on screen that
+share a material and a lightmap page are one mesh (`mergeSceneChunks`), so a battlefield such as act2 m02 (36 chunks,
+5 lightmap pages) stays inside the board's draw-call budget. A switched-off HIDDEN part is left out of that mesh.
 
 Owner decision (2026-10-12): the eleven scenes belong to the 0.2.5 asset pack. The maintainer's full release zip
 includes the extracted files. A lite package or a source install may download and extract them on that machine
diff --git a/public/js/render/board3d/load.js b/public/js/render/board3d/load.js
index 5303e9b2..e1063faa 100644
--- a/public/js/render/board3d/load.js
+++ b/public/js/render/board3d/load.js
@@ -195,6 +195,74 @@ export function parseSceneChunks(doc, buf) {
   return out;
 }
 
+/**
+ * Mesh bucket of a scene chunk. One material and one lightmap page are one draw. Water ignores the page: that shader
+ * has no lightmap (`scene.js` `sceneWaterMaterial`).
+ * @param {{ material?: string, lightmap?: number }} chunk
+ * @param {{ kind?: string }|null} info scene.json materials[name]
+ */
+export function sceneMaterialKey(chunk, info) {
+  return `${chunk?.material}|${info?.kind === 'water' ? '' : chunk?.lightmap}`;
+}
+
+/**
+ * One scene chunk from several that share a material bucket (`sceneMaterialKey`). Vertex attributes stay in the
+ * scene.bin layout (position f32×3, uv f32×2, lightmap uv f32×2, normal i8×4, colour u8×4) and indices are rewritten
+ * with the vertex offset; past 65535 vertices the index is 32-bit (WebGL2). A single chunk is returned as-is, so the
+ * pack's views of scene.bin stay shared. The caller passes chunks of one bucket that are on screen together: a
+ * file-level merge would bake a switched-off HIDDEN part into the base mesh.
+ * @param {object[]|null} chunks
+ * @returns {object|null}
+ */
+export function mergeSceneChunks(chunks) {
+  if (!Array.isArray(chunks) || chunks.length === 0) return null;
+  if (chunks.length === 1) return chunks[0];
+  const first = chunks[0];
+  let nv = 0, ni = 0, index32 = false;
+  for (const c of chunks) {
+    const n = c?.position?.length / 3;
+    if (!Number.isInteger(n) || n <= 0) throw new Error(`scene chunk ${c?.material}: ${c?.position?.length ?? 0} position components`);
+    if (c.material !== first.material) throw new Error(`scene merge mixes ${first.material} and ${c.material}`);
+    if (c.uv?.length !== n * 2 || c.uv1?.length !== n * 2 || c.normal?.length !== n * 4 || c.color?.length !== n * 4) {
+      throw new Error(`scene chunk ${c.material}: attributes do not match ${n} vertices`);
+    }
+    if (!c.index || c.index.length === 0) throw new Error(`scene chunk ${c.material}: no indices`);
+    nv += n;
+    ni += c.index.length;
+    if (c.index instanceof Uint32Array) index32 = true;
+  }
+  if (nv > 65535) index32 = true;
+  const position = new Float32Array(nv * 3);
+  const uv = new Float32Array(nv * 2);
+  const uv1 = new Float32Array(nv * 2);
+  const normal = new Int8Array(nv * 4);
+  const color = new Uint8Array(nv * 4);
+  const index = index32 ? new Uint32Array(ni) : new Uint16Array(ni);
+  let vo = 0, io = 0, bounds = null;
+  for (const c of chunks) {
+    const n = c.position.length / 3;
+    position.set(c.position, vo * 3);
+    uv.set(c.uv, vo * 2);
+    uv1.set(c.uv1, vo * 2);
+    normal.set(c.normal, vo * 4);
+    color.set(c.color, vo * 4);
+    for (let i = 0; i < c.index.length; i++) {
+      const v = c.index[i];
+      if (v < 0 || v >= n) throw new Error(`scene chunk ${c.material}: index ${v} out of ${n}`);
+      index[io + i] = v + vo;
+    }
+    vo += n;
+    io += c.index.length;
+    if (Array.isArray(c.bounds) && c.bounds.length >= 6) {
+      const b = c.bounds;
+      bounds = bounds
+        ? [Math.min(bounds[0], b[0]), Math.min(bounds[1], b[1]), Math.min(bounds[2], b[2]), Math.max(bounds[3], b[3]), Math.max(bounds[4], b[4]), Math.max(bounds[5], b[5])]
+        : b.slice();
+    }
+  }
+  return { material: first.material, lightmap: first.lightmap, group: '', bounds, position, uv, uv1, normal, color, index };
+}
+
 /** Ground rect [x0, y0, x1, y1] (board space) of every named group of chunks (the scene's switchable parts). */
 export function sceneGroupRects(chunks) {
   const out = {};
diff --git a/public/js/render/board3d/scene.js b/public/js/render/board3d/scene.js
index 0e08ce03..502b7806 100644
--- a/public/js/render/board3d/scene.js
+++ b/public/js/render/board3d/scene.js
@@ -19,6 +19,8 @@
 // static crates (merged, same material),
 // decals (MT_autochess_common), fence pipes, blowers (merged, unlit), gate boxes (additive + alpha, merged per
 // material), cyan field edges, terrain overlays (≤ 4), background plane + its shadow catcher — ~12–16 in total.
+// An official scene replaces the tiles, glass, decals, pipes and background with one mesh per material and lightmap
+// page of the parts the built areas show (load.js mergeSceneChunks). Devices, gates, edges and terrain stay.
 // The key light's shadow map is rendered only when the geometry changes (autoUpdate off).
 
 import { buildBoard, objToBoard, boxProjectUV, ROWS, COLS, DEVICE_H, AREAS } from './layout.js';
@@ -28,6 +30,7 @@ import {
   waterMaterial, mireMaterial, infectionMaterial, smogMaterial, dashTexture, environmentMap, sceneMaterial, sceneWaterMaterial,
 } from './materials.js';
 import { syncThreeCamera } from '../projection.js';
+import { mergeSceneChunks, sceneMaterialKey } from './load.js';
 
 /** Lighting rig (tuned against the official screenshots: bright even tops, darker sides, soft shadows). */
 export const LIGHTING = Object.freeze({
@@ -343,18 +346,29 @@ export class BoardScene {
     this.sceneRes.delete(pack.key);
   }
 
-  /** The official scene's meshes: one per chunk of a shown part (the base + the fields of the built areas). */
+  /**
+   * The official scene's meshes: the base plus the fields of the built areas, one mesh per material and lightmap
+   * page (`mergeSceneChunks`). A switched-off HIDDEN part is left out before the merge.
+   */
   _buildScene(pack) {
     const T = this.THREE;
     const res = this._sceneResources(pack);
     const infos = pack.doc?.materials || {};
     this.sceneWater = [];
-    let n = 0;
+    const buckets = new Map();
     for (const c of pack.chunks || []) {
       if (c.group && !sceneGroupVisible(pack.groups?.[c.group], this.area)) continue;
       const info = infos[c.material] || null;
+      const mk = sceneMaterialKey(c, info);
+      let bucket = buckets.get(mk);
+      if (!bucket) { bucket = { info, chunks: [] }; buckets.set(mk, bucket); }
+      bucket.chunks.push(c);
+    }
+    let n = 0;
+    for (const [mk, bucket] of buckets) {
+      const c = mergeSceneChunks(bucket.chunks);
+      const info = bucket.info;
       const water = info?.kind === 'water';
-      const mk = `${c.material}|${water ? '' : c.lightmap}`;
       let mat = res.mats.get(mk);
       if (!mat) {
         mat = water
diff --git a/test/render/board3d-scene.test.js b/test/render/board3d-scene.test.js
index ee87eed4..e07b0761 100644
--- a/test/render/board3d-scene.test.js
+++ b/test/render/board3d-scene.test.js
@@ -18,7 +18,8 @@ import { resolveUvTable } from '../../public/js/render/board3d/atlas.js';
 import { presetCamera } from '../../public/js/render/projection.js';
 import { sceneMaterial, sceneWaterMaterial, sceneBlend, focusUniforms, SCENE_LIGHT } from '../../public/js/render/board3d/materials.js';
 import {
-  parseSceneChunks, sceneGroupRects, loadScenePack, sceneListed, resetBoardPack, sceneGroup, SCENE_TEX_GROUP, SCENE_VERSION, SCENE_VERTEX_BYTES,
+  parseSceneChunks, sceneGroupRects, loadScenePack, sceneListed, resetBoardPack, sceneGroup, sceneMaterialKey, mergeSceneChunks,
+  SCENE_TEX_GROUP, SCENE_VERSION, SCENE_VERTEX_BYTES,
 } from '../../public/js/render/board3d/load.js';
 
 const ROOT = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '../..');
@@ -211,6 +212,45 @@ describe('scene chunks (load.js)', () => {
     assert.equal(parseSceneChunks(doc, null), null);
   });
 
+  test('sceneMaterialKey / mergeSceneChunks: one mesh per material and lightmap page; indices keep each quad', () => {
+    assert.equal(sceneMaterialKey({ material: 'M', lightmap: 3 }, { kind: 'lit' }), 'M|3');
+    assert.equal(sceneMaterialKey({ material: 'M', lightmap: 0 }, null), 'M|0');
+    assert.equal(sceneMaterialKey({ material: 'W', lightmap: -1 }, { kind: 'water' }), 'W|');
+    assert.equal(sceneMaterialKey({ material: 'W', lightmap: 2 }, { kind: 'water' }), 'W|', 'water has no lightmap page');
+    const { doc, bin } = fakeScene([{ material: 'M', x0: 0, y0: 0 }, { material: 'M', x0: 3, y0: 1, group: 'HIDDEN@1' }]);
+    const chunks = parseSceneChunks(doc, bin);
+    assert.equal(mergeSceneChunks([chunks[0]]), chunks[0], 'a single chunk stays the scene.bin view');
+    assert.equal(mergeSceneChunks([]), null);
+    assert.equal(mergeSceneChunks(null), null);
+    const merged = mergeSceneChunks(chunks);
+    assert.equal(merged.position.length / 3, 8);
+    assert.ok(merged.index instanceof Uint16Array);
+    assert.deepEqual([...merged.index], [0, 1, 2, 0, 2, 3, 4, 5, 6, 4, 6, 7]);
+    assert.equal(merged.position[12], 3, 'the second quad keeps its board position');
+    assert.equal(merged.normal[18], 127);
+    assert.deepEqual([...merged.color.slice(16, 20)], [255, 255, 255, 255]);
+    assert.deepEqual([...merged.uv1.slice(8, 12)], [0, 0, 0.5, 0]);
+    assert.deepEqual([...chunks[1].index], [0, 1, 2, 0, 2, 3], 'the source chunk is not rewritten');
+    assert.deepEqual(merged.bounds, [0, 0, 0, 4, 2, 0]);
+    const big = new Float32Array(65535 * 3);
+    const one = {
+      material: 'M', lightmap: 0, group: '', bounds: null,
+      position: big, uv: new Float32Array(65535 * 2), uv1: new Float32Array(65535 * 2),
+      normal: new Int8Array(65535 * 4), color: new Uint8Array(65535 * 4), index: new Uint16Array([0, 0, 0]),
+    };
+    const extra = {
+      material: 'M', lightmap: 0, group: 'HIDDEN@1', bounds: null,
+      position: new Float32Array([9, 8, 7]), uv: new Float32Array(2), uv1: new Float32Array(2),
+      normal: new Int8Array(4), color: new Uint8Array(4), index: new Uint16Array([0, 0, 0]),
+    };
+    const wide = mergeSceneChunks([one, extra]);
+    assert.ok(wide.index instanceof Uint32Array, 'past 65535 vertices the index is 32-bit');
+    assert.equal(wide.position.length / 3, 65536);
+    assert.equal(wide.index[3], 65535);
+    assert.equal(wide.position[65535 * 3], 9);
+    assert.throws(() => mergeSceneChunks([{ ...chunks[0], material: 'Other' }, chunks[1]]), /mixes/);
+  });
+
   test('sceneGroupRects / sceneGroupVisible: the official sub-graphics are the fields of the built areas', () => {
     const { doc, bin } = fakeScene(PARTS);
     const rects = sceneGroupRects(parseSceneChunks(doc, bin));
@@ -305,9 +345,17 @@ describe('BoardScene with an official scene (stub renderer)', () => {
     assert.ok(!board.meshes.board && !board.meshes.glass && !board.meshes.decal && !board.meshes.pipe && !board.meshes.bg && !board.meshes.bgShadow);
     assert.ok(board.meshes.crates && board.meshes.edges && board.meshes.mire, Object.keys(board.meshes).join());
     const meshes = sceneMeshes(board);
-    assert.equal(meshes.length, 4, 'base ×2 + the left normal field ×2 (AREAS.normal)');
+    assert.equal(meshes.length, 3, 'base + the left field: the two M quads share one mesh');
+    assert.deepEqual(meshes.map((m) => m.geometry.getAttribute('position').count).sort((a, b) => a - b), [4, 4, 8]);
+    const xs = meshes.flatMap((m) => {
+      const a = m.geometry.getAttribute('position').array;
+      const out = [];
+      for (let i = 0; i < a.length; i += 3) out.push(a[i]);
+      return out;
+    });
+    assert.ok(xs.includes(9) && xs.includes(4), 'base and the left field');
+    assert.ok(!xs.includes(16) && !xs.includes(11), 'the right field and the boss field stay out');
     for (const m of meshes) {
-      assert.equal(m.geometry.getAttribute('position').count, 4);
       assert.ok(m.geometry.getAttribute('aLm') && m.geometry.getAttribute('aColor').normalized && m.geometry.getAttribute('normal').normalized);
       assert.equal(m.castShadow, false);
     }
@@ -328,9 +376,9 @@ describe('BoardScene with an official scene (stub renderer)', () => {
     assert.equal(lit.uniforms.uMap.value.colorSpace, THREE.SRGBColorSpace);
     assert.equal(lit.uniforms.uLm.value.colorSpace, THREE.NoColorSpace);
     board.setArea(AREAS.boss);
-    assert.equal(sceneMeshes(board).length, 3, 'base ×2 + the boss field');
+    assert.equal(sceneMeshes(board).length, 2, 'base + the boss field, the two M quads merged');
     board.setArea(AREAS.unite);
-    assert.equal(sceneMeshes(board).length, 5, 'base ×2 + both normal fields (2 + 1)');
+    assert.equal(sceneMeshes(board).length, 3, 'base + both normal fields: M merged, water, cutout');
     assert.equal(sceneMeshes(board).find((m) => m.material.uniforms.uMap).material, lit, 'same material object');
     assert.equal(board.sceneRes.size, 1);
     board.destroy();
@@ -353,6 +401,27 @@ describe('BoardScene with an official scene (stub renderer)', () => {
     board.destroy();
   });
 
+  test('a different lightmap page stays its own mesh; water pages share one', () => {
+    const board = new BoardScene(THREE, fakePack(), { renderer: stubRenderer() });
+    const parts = [
+      { material: 'M', x0: 4, y0: 9, lightmap: 0, group: 'HIDDEN@1' },
+      { material: 'M', x0: 9, y0: 15, lightmap: 1 },
+      { material: 'W', x0: 5, y0: 9, lightmap: 0, group: 'HIDDEN@1' },
+      { material: 'W', x0: 6, y0: 9, lightmap: 1, group: 'HIDDEN@1' },
+    ];
+    const { doc, bin } = fakeScene(parts);
+    const chunks = parseSceneChunks(doc, bin);
+    board.setScenePack(stage.id, { key: 'split', stage: stage.id, doc, chunks, groups: sceneGroupRects(chunks), images: { tex: {}, lm: [] } });
+    board.setStage(stage);
+    const meshes = sceneMeshes(board);
+    assert.equal(meshes.length, 3, 'M|0, M|1, and one water mesh');
+    const water = meshes.filter((m) => m.material.uniforms.uDeep);
+    assert.equal(water.length, 1);
+    assert.equal(water[0].geometry.getAttribute('position').count, 8, 'both water quads');
+    assert.equal(board.sceneWater.length, 1);
+    board.destroy();
+  });
+
   test('a scene whose chunks are all hidden parts of other areas keeps the procedural board', () => {
     const board = new BoardScene(THREE, fakePack(), { renderer: stubRenderer() });
     const { doc, bin } = fakeScene([{ material: 'M', x0: 10, y0: 3, group: 'HIDDEN@3' }]);
@@ -391,4 +460,35 @@ describe('extracted scenes (when scene bundles were extracted here)', { skip: !O
       assert.ok(L && Math.abs(Math.hypot(...L.dir) - 1) < 1e-3 && L.dir[2] > 0, 'the key light shines down on the board');
     });
   }
+
+  test('each built area is one mesh per material and lightmap, with every shown vertex and no switched-off part', () => {
+    const views = [['normal', AREAS.normal], ['boss', AREAS.boss], ['unite', AREAS.unite]];
+    for (const g of Object.keys(groups).filter((k) => k.startsWith('scene/act'))) {
+      if (!existsSync(file(groups[g].scene?.path || '/x'))) continue;
+      const doc = JSON.parse(readFileSync(file(groups[g].scene.path), 'utf8'));
+      const bin = readFileSync(file(groups[g].bin.path));
+      const chunks = parseSceneChunks(doc, bin.buffer.slice(bin.byteOffset, bin.byteOffset + bin.length));
+      const rects = sceneGroupRects(chunks);
+      const stage = stages[doc.stage];
+      const board = new BoardScene(THREE, fakePack(), { renderer: stubRenderer() });
+      board.setScenePack(doc.stage, { key: g, stage: doc.stage, doc, chunks, groups: rects, images: { tex: {}, lm: [] } });
+      board.setStage(stage);
+      for (const [name, area] of views) {
+        board.setArea(area);
+        const shown = chunks.filter((c) => !c.group || sceneGroupVisible(rects[c.group], area));
+        const keys = new Set(shown.map((c) => sceneMaterialKey(c, doc.materials[c.material])));
+        const meshes = sceneMeshes(board);
+        assert.equal(meshes.length, keys.size, `${doc.stage} ${name}: ${shown.length} chunks → ${keys.size} meshes`);
+        assert.ok(meshes.length > 0 && meshes.length <= 16, `${doc.stage} ${name}: ${meshes.length} scene draw calls`);
+        let verts = 0;
+        for (const m of meshes) verts += m.geometry.getAttribute('position').count;
+        assert.equal(verts, shown.reduce((a, c) => a + c.position.length / 3, 0), `${doc.stage} ${name} vertices`);
+        if (name !== 'unite') assert.ok(board.root.children.length <= 19, `${doc.stage} ${name}: ${board.root.children.length} meshes beside one battle device still fit 20 draws`);
+      }
+      assert.equal(board.meshes.board, undefined, `${doc.stage}: the scene replaces the metal tiles`);
+      board.setScenePack(doc.stage, null);
+      assert.ok(board.meshes.board && board.meshes.bg, `${doc.stage}: dropping the scene restores the metal board`);
+      board.destroy();
+    }
+  });
 });
diff --git a/test/ui/playtest2.real.e2e.test.js b/test/ui/playtest2.real.e2e.test.js
index 6cb6a3fd..e0bf9011 100644
--- a/test/ui/playtest2.real.e2e.test.js
+++ b/test/ui/playtest2.real.e2e.test.js
@@ -1,6 +1,7 @@
 // Real-server browser E2E of user playtest #2 item 10 (+ item 6 on the real flow): the boss round's prep shows the
 // player's own half of the boss field (tiles, gates, objective) and placing works — solo (标准: R9 最终攻势; 险境:
-// R15 隐秘核心) and co-op (two humans: the host prepares on the LEFT half, the guest on the mirrored RIGHT half) — then
+// R15 隐秘核心) and co-op (two humans: each prepares on the half m.public.bossPairs assigns, the second of the pair
+// on the mirrored RIGHT half) — then
 // the Final Assault starts with the placed units on the boss field. Along the way (item 6): the pen stays hidden with
 // the board (🔍▶▶ shows it, 🔍◀◀ "返回战场" hides it again), scouting a teammate (前往查看) and coming back, and in
 // the boss battle.
@@ -21,6 +22,7 @@ import assert from 'node:assert/strict';
 import { existsSync } from 'node:fs';
 import path from 'node:path';
 import { Client, ROOT, sleep, hasChrome, startRealServer, problemsOf, waitForFunctionLong } from '../e2e/client.mjs';
+import { prepCamera } from '../../public/js/ui/gameLogic/camera.js';
 
 const ENABLED = process.env.SP_E2E === '1' && hasChrome() && existsSync(path.join(ROOT, 'public/assets'));
 const ONLY = process.env.SP_P2_REAL || '';
@@ -101,6 +103,29 @@ async function placeOne(c, dir = 'RIGHT') {
   throw new Error(`${c.label}: nothing could be placed`);
 }
 
+/**
+ * The half this client prepares on, from the published pairing (`m.public.bossPairs` through `prepCamera`).
+ * The first of a pair is on the left half; the second is on the mirrored right half. Seat order is not a side.
+ */
+async function assignedBossSide(c) {
+  const snap = await c.page.evaluate(() => {
+    const s = globalThis.__SP__.store.get();
+    const pub = s.match.public || {};
+    return {
+      me: s.me?.playerId ?? null,
+      phase: pub.phase ?? null, round: pub.round ?? null, bossRound: pub.bossRound ?? null, hiddenRound: pub.hiddenRound ?? null,
+      bossPairs: pub.bossPairs ?? null,
+      players: (pub.players || []).map((p) => ({ playerId: p.playerId, seat: p.seat, alive: p.alive !== false })),
+    };
+  });
+  const cam = prepCamera(snap, snap.me);
+  const pair = (Array.isArray(snap.bossPairs) ? snap.bossPairs : []).find((g) => Array.isArray(g) && g.includes(snap.me));
+  assert.equal(cam.kind, 'bossPrep', `${c.label}: boss-round prep (pairs ${JSON.stringify(snap.bossPairs)})`);
+  assert.ok(pair, `${c.label}: a published pair`);
+  assert.equal(cam.opts.side, pair.indexOf(snap.me) % 2 === 1 ? 'R' : 'L', `${c.label}: the side is the pair index`);
+  return { side: cam.opts.side, me: snap.me, pair, bossPairs: snap.bossPairs };
+}
+
 /** The boss-round prep checks shared by every variant. */
 async function checkBossPrep(c, side, tag) {
   const v = await viewState(c);
@@ -344,7 +369,7 @@ describe('user playtest #2 item 10 — boss-round prep on the boss field (real s
     }
   });
 
-  test('co-op 险境 (R14): host on the left half, guest on the mirrored right half; scouting and 返回 keep the pen hidden', { skip: only('coop'), timeout: 10 * 60 * 1000 }, async () => {
+  test('co-op 险境 (R14): each player on the half bossPairs assigns (the right half mirrored); scouting and 返回 keep the pen hidden', { skip: only('coop'), timeout: 10 * 60 * 1000 }, async () => {
     const srv = await startRealServer({ fast: { timerScale: 1, combatSpeed: 8, startRound: 'boss', items: ['chess_item_6_03_m'] } });
     const P = await pptr();
     const host = new Client(P, srv.base, 'host', { prefix: 'fix' });
@@ -386,8 +411,12 @@ describe('user playtest #2 item 10 — boss-round prep on the boss field (real s
       await sleep(1800);
       const hs = await host.st();
       assert.equal(hs.round, hs.bossRound, 'the boss round');
-      await checkBossPrep(host, 'L', 'host');
-      await checkBossPrep(guest, 'R', 'guest');
+      const hostSeat = await assignedBossSide(host);
+      const guestSeat = await assignedBossSide(guest);
+      assert.ok(hostSeat.pair.includes(guestSeat.me), `the two players share a pair (${JSON.stringify(hostSeat.bossPairs)})`);
+      assert.notEqual(hostSeat.side, guestSeat.side, 'a pair occupies both halves');
+      await checkBossPrep(host, hostSeat.side, 'host');
+      await checkBossPrep(guest, guestSeat.side, 'guest');
       const hp = await placeOne(host, 'RIGHT');
       const gp = await placeOne(guest, 'RIGHT');
       await sleep(600);
@@ -404,12 +433,14 @@ describe('user playtest #2 item 10 — boss-round prep on the boss field (real s
         const w = await viewState(host);
         assert.equal(w.penVisible, 0, 'scouting: no pen figure with the teammate\'s board');
         assert.ok(w.band[1] <= 13, `scouting: no pen rows (${w.band})`);
+        assert.equal(w.camKind, 'bossPrep', 'scouting: the boss field');
+        assert.deepEqual(w.prepField, { kind: 'bossPrep', side: guestSeat.side, mirror: guestSeat.side === 'R' }, 'scouting: the teammate\'s half');
         await host.click('.gm__watching button, .team__back', null, { timeout: 4000 });
         await host.page.waitForFunction(() => document.querySelector('.gm')?.dataset.camera === 'bossPrep', { timeout: 6000 });
         await sleep(900);
         const back = await viewState(host);
         assert.equal(back.penVisible, 0, '返回: no pen figure');
-        assert.deepEqual(back.prepField, { kind: 'bossPrep', side: 'L', mirror: false }, '返回: the own boss half again');
+        assert.deepEqual(back.prepField, { kind: 'bossPrep', side: hostSeat.side, mirror: hostSeat.side === 'R' }, '返回: the own boss half again');
       }
       await penRoundTrip(guest, 'guest');
       // Real clients open their own 教鞭 candidates together; refreshing one tab restores that same private choice.
@@ -454,8 +485,8 @@ describe('user playtest #2 item 10 — boss-round prep on the boss field (real s
         await c.page.waitForFunction(() => globalThis.__SP__.store.get().match.private.personalChoice === null, { timeout: 6000 });
       }
       for (const c of [host, guest]) await c.click('.readybtn');
-      await checkBossBattle(host, hp, 'L', 'host');
-      await checkBossBattle(guest, gp, 'R', 'guest');
+      await checkBossBattle(host, hp, hostSeat.side, 'host');
+      await checkBossBattle(guest, gp, guestSeat.side, 'guest');
       assert.deepEqual(problemsOf([host, guest]), []);
     } finally {
       for (const c of [host, guest]) if (c.problems.length) console.log(c.label, c.problems.slice(0, 20).join('\n'));