fix(UC-02): arch review — furniture x/z offsets + ceiling chain fidelity

- Add x_offset/z_offset to PositionedBlock for multi-block furniture clusters
- Furniture items now spread across 2-3 positions (matching original Java code)
- Offsets multiplied by inward direction for correct corner orientation
- Fix has_ceiling_chain: only oubliette has ceiling chains (was true for all 6)
- Fix firstCornerSpecial: oubliette cauldron uses x/z offset +1 (inward diagonal)
- Update parser to read x_offset/z_offset (defaults to 0)

src/main/java/com/tiedup/remake/worldgen/DecorationConfig.java

@@ -27,10 +27,17 @@ public record DecorationConfig(
 ) {
 
     /**
-     * A block state with an associated Y offset for positioned placement.
+     * A block state with positional offsets for placement.
      *
      * @param state   the block state to place
+     * @param xOffset horizontal X offset from base position (0 = no offset)
      * @param yOffset vertical offset from the base position
+     * @param zOffset horizontal Z offset from base position (0 = no offset)
      */
-    public record PositionedBlock(BlockState state, int yOffset) {}
+    public record PositionedBlock(BlockState state, int xOffset, int yOffset, int zOffset) {
+        /** Convenience constructor for Y-offset-only blocks (most common case). */
+        public PositionedBlock(BlockState state, int yOffset) {
+            this(state, 0, yOffset, 0);
+        }
+    }
 }

src/main/java/com/tiedup/remake/worldgen/HangingCagePiece.java

@@ -660,24 +660,35 @@ public class HangingCagePiece extends StructurePiece {
         }
 
         // First corner special (e.g. water cauldron, skull, TNT, sculk catalyst)
+        // x/z offsets are multiplied by inward direction (toward room center)
         if (deco.firstCornerSpecial() != null && corners.length > 0) {
             int[] sc = corners[0];
-            if (layout.isInShape(sc[0], sc[1]) && !layout.isWall(sc[0], sc[1])) {
+            int dirX = sc[0] < 6 ? 1 : -1;
+            int dirZ = sc[1] < 6 ? 1 : -1;
+            int scx = sc[0] + deco.firstCornerSpecial().xOffset() * dirX;
+            int scz = sc[1] + deco.firstCornerSpecial().zOffset() * dirZ;
+            if (layout.isInShape(scx, scz) && !layout.isWall(scx, scz)) {
                 safeSetBlock(level,
-                    new BlockPos(baseX + sc[0], floorY + deco.firstCornerSpecial().yOffset(), baseZ + sc[1]),
+                    new BlockPos(baseX + scx, floorY + deco.firstCornerSpecial().yOffset(), baseZ + scz),
                     deco.firstCornerSpecial().state(), chunkBB);
             }
         }
 
-        // Furniture cluster at corners[1] (e.g. barrel+brewing_stand, soul_campfire+cauldron)
+        // Furniture cluster at corners[1] — each item has x/z offsets relative to the
+        // base furniture position. x_offset/z_offset values are multiplied by the
+        // inward direction (toward room center) to handle all 4 corner orientations.
         if (corners.length > 1) {
             int[] fc = corners[1];
-            int fcx = fc[0] + (fc[0] < 6 ? 1 : -1);
-            int fcz = fc[1] + (fc[1] < 6 ? 1 : -1);
-            if (layout.isInShape(fcx, fcz) && !layout.isWall(fcx, fcz)) {
-                for (DecorationConfig.PositionedBlock pb : deco.furnitureCluster()) {
+            int dirX = fc[0] < 6 ? 1 : -1;
+            int dirZ = fc[1] < 6 ? 1 : -1;
+            int fcx = fc[0] + dirX;
+            int fcz = fc[1] + dirZ;
+            for (DecorationConfig.PositionedBlock pb : deco.furnitureCluster()) {
+                int px = fcx + pb.xOffset() * dirX;
+                int pz = fcz + pb.zOffset() * dirZ;
+                if (layout.isInShape(px, pz) && !layout.isWall(px, pz)) {
                     safeSetBlock(level,
-                        new BlockPos(baseX + fcx, floorY + pb.yOffset(), baseZ + fcz),
+                        new BlockPos(baseX + px, floorY + pb.yOffset(), baseZ + pz),
                         pb.state(), chunkBB);
                 }
             }

src/main/java/com/tiedup/remake/worldgen/RoomThemeParser.java

@@ -433,7 +433,7 @@ public final class RoomThemeParser {
     }
 
     /**
-     * Parse a single positioned block: { "block": "...", "y_offset": 0 }
+     * Parse a single positioned block: { "block": "...", "x_offset": 0, "y_offset": 0, "z_offset": 0 }
      */
     @Nullable
     private static DecorationConfig.PositionedBlock parsePositionedBlock(
@@ -445,8 +445,10 @@ public final class RoomThemeParser {
         BlockState state = parseBlockState(blockStr, fileId);
         if (state == null) return null;
 
+        int xOffset = getIntOrDefault(obj, "x_offset", 0);
         int yOffset = getIntOrDefault(obj, "y_offset", 0);
-        return new DecorationConfig.PositionedBlock(state, yOffset);
+        int zOffset = getIntOrDefault(obj, "z_offset", 0);
+        return new DecorationConfig.PositionedBlock(state, xOffset, yOffset, zOffset);
     }
 
     // ===== Primitive Helpers =====