修复顶角墙缺左半：DS1 只列 type 3，引擎会自己补画 type 4

现象：墙角（两段墙交汇的上顶点）左边一块渲染不正常——角的左脸缺失，右半的墙基露出来，
接缝处出现台阶/突块。例：第三章「下水道二层」（sewertreasure1）有 5 处。

根因：D2 的顶角美术是两半拼的，DS1 只存「顶角右半」（type 3），左半（type 4）从不列出；
引擎在装配房间瓦片时会自己补——
  DRLGROOMTILE_InitWallTileData（D2Common/DRLG/RoomTile.cpp，1.10f 0x6FD889C0）:
      if (nTileType == TILETYPE_WALL_TOP_CORNER_RIGHT)
          再以同格的同份 packed tile 信息追加一个 TILETYPE_WALL_TOP_CORNER_LEFT 图块
我们的渲染器只画 DS1 列的引用，所以这一步从未发生。

改动：buildIsoMapScene 的墙循环里，type 3 解析成功后，用同一 style:sequence 精确解析
type 4 伙伴，同格、按各自的 minBlockY 规则绘制，并把它并入碰撞栅格；新增
scene.cornerPairs / scene.missingCornerPairs 供校验使用。verify-tiles 增加两条断言。

实测：35 关共 411 个 type 3，全部有 type 4 伙伴（缺失 0），墙绘制数 9103 → 9514；
「下水道二层」72 → 77 面墙，与 5 个顶角一致。

scripts/verify-tiles.ts

@@ -12,7 +12,10 @@
 //   3. `looseRefs == 0`（没有任何引用走类型无关兜底）与 `missingTiles == 0`——
 //      这两条合起来保证"画出的类型 == 引用的类型"；
 //   4. 位置自洽：地面 `y == (cx+cy)*40` 且瓦片 `minBlockY == 0`；
-//      墙 `y == (cx+cy)*40 + minBlockY + 80`；屋顶 `y == (cx+cy)*40 - roofHeight`。
+//      墙 `y == (cx+cy)*40 + minBlockY + 80`；屋顶 `y == (cx+cy)*40 - roofHeight`；
+//   5. 顶角（DS1 `type 3`）必须连带画出左半（`type 4`）——引擎在
+//      `DRLGROOMTILE_InitWallTileData` 里就是这么做的，DS1 自己从不列左半。
+//      漏掉它时墙角会缺一块，看起来像"渲染不正常"。
 //
 //   node scripts/verify-tiles.ts [--dir=samples/d2] [--limit=35]
 //
@@ -69,6 +72,9 @@ async function main(): Promise<void> {
   let looseRefs = 0
   let missingTiles = 0
   let positionMismatch = 0
+  let cornerRefs = 0
+  let cornerPairs = 0
+  let missingCornerPairs = 0
   const worst: [number, string][] = []
 
   for (const row of tables.levels.rows) {
@@ -99,6 +105,13 @@ async function main(): Promise<void> {
 
     const seed = levelSeed(info.ds1Names[0]!)
     const scene = buildIsoMapScene(ds1, libs, seed)
+    for (const cellRef of ds1.cells.flat()) {
+      for (const wall of cellRef.walls) {
+        if (!wall.hidden && wall.prop1 !== 0 && wall.type === 3) cornerRefs += 1
+      }
+    }
+    cornerPairs += scene.cornerPairs
+    missingCornerPairs += scene.missingCornerPairs
     looseRefs += scene.looseRefs
     missingTiles += scene.missingTiles
 
@@ -139,6 +152,9 @@ async function main(): Promise<void> {
   check('没有任何引用走类型无关兜底', looseRefs === 0, `looseRefs ${String(looseRefs)}`)
   check('没有解析不到的引用', missingTiles === 0, `missingTiles ${String(missingTiles)}`)
   check('地面/墙/屋顶的位置公式自洽', positionMismatch === 0, `${String(positionMismatch)} 个不符`)
+  check('每个顶角右半都画出了左半伙伴', cornerRefs > 0 && cornerPairs === cornerRefs,
+    `${String(cornerPairs)}/${String(cornerRefs)} 个 type-3 墙带了 type-4 伙伴`)
+  check('没有解析不到的顶角伙伴', missingCornerPairs === 0, `${String(missingCornerPairs)} 个`)
   if (worst.length > 0 && worst[0]![0] > 0) console.log(`   最严重：${worst.slice(0, 5).map(([pct, name]) => `${name} ${pct.toFixed(1)}%`).join('，')}`)
 
   const passed = checks.filter(entry => entry.ok).length

src/game/d2map.ts

@@ -66,6 +66,19 @@ const FLOOR_TILE_TYPE = 0
  * painter order and out of the wall offset rule.
  */
 const ROOF_WALL_TYPE = 15
+/**
+ * DS1 wall types of the two halves of a "top" (north) corner.
+ *
+ * The engine never draws the right half alone: `DRLGROOMTILE_InitWallTileData`
+ * (`D2Common/DRLG/RoomTile.cpp`) adds a `TILETYPE_WALL_TOP_CORNER_RIGHT` wall and
+ * then, in the same cell and with the same packed tile information, a second
+ * `TILETYPE_WALL_TOP_CORNER_LEFT` tile — fetched from the tile cache with the same
+ * style/sequence. Without that companion the corner is missing its left face, which
+ * is what a "broken corner block" looks like on screen.
+ */
+const TOP_CORNER_RIGHT_TYPE = 3
+/** The companion half of {@link TOP_CORNER_RIGHT_TYPE}. */
+const TOP_CORNER_LEFT_TYPE = 4
 /** One tile to draw, in screen pixels. */
 export interface IsoDraw {
   /** Index into {@link IsoMapScene.frames}. */
@@ -155,6 +168,15 @@ export interface IsoMapScene {
    * `npm run verify:tiles` exists to catch.
    */
   readonly looseRefs: number
+  /**
+   * Top-corner-right walls that got their left half drawn as well.
+   *
+   * The engine always adds the companion tile (`DRLGROOMTILE_InitWallTileData`), so
+   * this should equal the number of type-3 walls in the level.
+   */
+  readonly cornerPairs: number
+  /** Top-corner-right walls whose left half could not be resolved (should be 0). */
+  readonly missingCornerPairs: number
 }
 
 /**
@@ -405,6 +427,8 @@ export function buildIsoMapScene(level: Ds1, libraries: readonly Dt1[], seed = 0
   // skipping them would silently drop blocking sub-tiles.
   let shadowBlocked = 0
   let looseRefs = 0
+  let cornerPairs = 0
+  let missingCornerPairs = 0
   const stamp = (cellX: number, cellY: number, tile: Dt1Tile): void => {
     for (let subY = 0; subY < SUB_TILES_PER_TILE; subY += 1) {
       for (let subX = 0; subX < SUB_TILES_PER_TILE; subX += 1) {
@@ -494,6 +518,29 @@ export function buildIsoMapScene(level: Ds1, libraries: readonly Dt1[], seed = 0
           rawWalls.push(draw)
         }
         stamp(cellX, cellY, tile)
+
+        // A top-corner-right wall drags its left half along (see
+        // {@link TOP_CORNER_RIGHT_TYPE}): same cell, same style/sequence, resolved as
+        // a type-4 tile, drawn with its own block shift like any other wall. The
+        // engine's DS1s never list the left half themselves, so this is the only way
+        // the corner gets both faces — 411 of them across the 35 preset levels.
+        if (tile.type === TOP_CORNER_RIGHT_TYPE) {
+          const companion = resolveExactType(pool, wall.style, wall.sequence, TOP_CORNER_LEFT_TYPE, cellX, cellY, seed)
+          if (companion === undefined) {
+            missingCornerPairs += 1
+            noteMissing('corner-left', wall.style, wall.sequence, TOP_CORNER_LEFT_TYPE, cellX, cellY)
+          } else {
+            const leftTile = libraries[companion.library]!.tiles[companion.tile]!
+            rawWalls.push({
+              frameIndex: frameFor(companion.library, companion.tile),
+              x: orthoX + TILE_ANCHOR_X,
+              y: orthoY + leftTile.minBlockY + WALL_SURFACE_HEIGHT,
+              cellX, cellY, library: companion.library, tile: companion.tile,
+            })
+            cornerPairs += 1
+            stamp(cellX, cellY, leftTile)
+          }
+        }
       }
     }
   }
@@ -540,6 +587,8 @@ export function buildIsoMapScene(level: Ds1, libraries: readonly Dt1[], seed = 0
     clippedTiles,
     shadowBlockedSubtiles: shadowBlocked,
     looseRefs,
+    cornerPairs,
+    missingCornerPairs,
     duplicateRefs: pool.duplicates,
   }
 }