diff --git a/src/index.html b/src/index.html
index 70c9cbe..961617d 100644
--- a/src/index.html
+++ b/src/index.html
@@ -76,7 +76,7 @@
     <div id="room-list"></div>
   </div>
 
-  <div id="info">Click a room to select it. Scroll to zoom, drag to orbit.</div>
+  <div id="info">Click a room to select it. Click furniture to edit. Scroll to zoom, drag to orbit.</div>
 
   <script type="importmap">
   {
@@ -88,16 +88,35 @@
   </script>
   <script type="module">
     import { HouseRenderer } from './renderer.js';
+    import { DesignState } from './state.js';
+    import { InteractionManager } from './interaction.js';
 
     const viewer = document.getElementById('viewer');
-    const renderer = new HouseRenderer(viewer);
+    const houseRenderer = new HouseRenderer(viewer);
 
     let selectedRoom = null;
+    let designState = null;
+    let interaction = null;
 
-    renderer.loadHouse('../data/sample-house.json').then(async (house) => {
+    houseRenderer.loadHouse('../data/sample-house.json').then(async (house) => {
       document.getElementById('house-name').textContent = house.name;
-      await renderer.loadCatalog('../data/furniture-catalog.json');
-      await renderer.loadDesign('../designs/sample-house-design.json');
+      await houseRenderer.loadCatalog('../data/furniture-catalog.json');
+      const design = await houseRenderer.loadDesign('../designs/sample-house-design.json');
+
+      // Initialize state and interaction manager
+      designState = new DesignState(design);
+      interaction = new InteractionManager(houseRenderer, designState);
+
+      interaction.onChange((type, detail) => {
+        if (type === 'select') {
+          document.getElementById('info').textContent =
+            `Selected: ${detail.itemName} — R to rotate, Delete to remove, Escape to deselect`;
+        } else if (type === 'deselect') {
+          document.getElementById('info').textContent =
+            'Click a room to select it. Click furniture to edit. Scroll to zoom, drag to orbit.';
+        }
+      });
+
       buildFloorButtons();
       buildRoomList();
     }).catch(err => {
@@ -108,12 +127,12 @@
     function buildFloorButtons() {
       const container = document.getElementById('floor-buttons');
       container.innerHTML = '';
-      for (const floor of renderer.getFloors()) {
+      for (const floor of houseRenderer.getFloors()) {
         const btn = document.createElement('button');
-        btn.className = 'floor-btn' + (floor.index === renderer.currentFloor ? ' active' : '');
+        btn.className = 'floor-btn' + (floor.index === houseRenderer.currentFloor ? ' active' : '');
         btn.textContent = floor.name;
         btn.addEventListener('click', () => {
-          renderer.showFloor(floor.index);
+          houseRenderer.showFloor(floor.index);
           document.querySelectorAll('.floor-btn').forEach(b => b.classList.remove('active'));
           btn.classList.add('active');
           buildRoomList();
@@ -126,7 +145,7 @@
     function buildRoomList() {
       const container = document.getElementById('room-list');
       container.innerHTML = '';
-      for (const room of renderer.getRooms()) {
+      for (const room of houseRenderer.getRooms()) {
         const item = document.createElement('div');
         item.className = 'room-item';
         item.dataset.roomId = room.id;
@@ -138,11 +157,11 @@
 
     function selectRoom(roomId) {
       selectedRoom = roomId;
-      renderer.focusRoom(roomId);
+      houseRenderer.focusRoom(roomId);
       document.querySelectorAll('.room-item').forEach(el => {
         el.classList.toggle('active', el.dataset.roomId === roomId);
       });
-      const room = renderer.getRooms().find(r => r.id === roomId);
+      const room = houseRenderer.getRooms().find(r => r.id === roomId);
       if (room) {
         document.getElementById('info').textContent = `${room.name} (${room.nameEN}) — ${room.area} m²`;
       }
@@ -151,11 +170,6 @@
     viewer.addEventListener('roomclick', (e) => {
       selectRoom(e.detail.roomId);
     });
-
-    viewer.addEventListener('furnitureclick', (e) => {
-      const d = e.detail;
-      document.getElementById('info').textContent = `${d.itemName} — in ${renderer.getRooms().find(r => r.id === d.roomId)?.name || d.roomId}`;
-    });
   </script>
 </body>
 </html>
diff --git a/src/interaction.js b/src/interaction.js
new file mode 100644
index 0000000..6c5a202
--- /dev/null
+++ b/src/interaction.js
@@ -0,0 +1,327 @@
+import * as THREE from 'three';
+
+/**
+ * InteractionManager — mode system, selection, keyboard shortcuts.
+ *
+ * Modes: view (default) | select | move | rotate | place
+ * Receives HouseRenderer + DesignState, hooks into renderer events.
+ */
+export class InteractionManager {
+  constructor(renderer, state) {
+    this.renderer = renderer;
+    this.state = state;
+    this.mode = 'view';
+    this.selectedObject = null;
+    this.selectedRoomId = null;
+    this.selectedIndex = -1;
+
+    this._outlineMaterial = new THREE.MeshBasicMaterial({
+      color: 0x00e5ff,
+      wireframe: true,
+      transparent: true,
+      opacity: 0.6
+    });
+    this._outlineGroup = null;
+
+    this._listeners = new Set();
+
+    // Bind event handlers (keep references for dispose)
+    this._onFurnitureClick = this._onFurnitureClick.bind(this);
+    this._onRoomClick = this._onRoomClick.bind(this);
+    this._onKeyDown = this._onKeyDown.bind(this);
+    this._onFloorChange = this._onFloorChange.bind(this);
+
+    this.renderer.container.addEventListener('furnitureclick', this._onFurnitureClick);
+    this.renderer.container.addEventListener('roomclick', this._onRoomClick);
+    this.renderer.container.addEventListener('floorchange', this._onFloorChange);
+    window.addEventListener('keydown', this._onKeyDown);
+
+    // Listen to DesignState changes to keep scene in sync
+    this._unsubState = this.state.onChange((type, detail) => this._onStateChange(type, detail));
+  }
+
+  // ---- Mode system ----
+
+  setMode(newMode) {
+    if (this.mode === newMode) return;
+    const oldMode = this.mode;
+    this.mode = newMode;
+
+    // Leaving select/move/rotate means clear selection
+    if (newMode === 'view') {
+      this.clearSelection();
+    }
+
+    this._emit('modechange', { oldMode, newMode });
+  }
+
+  // ---- Selection ----
+
+  select(meshGroup) {
+    if (this.selectedObject === meshGroup) return;
+    this.clearSelection();
+
+    this.selectedObject = meshGroup;
+    this.selectedRoomId = meshGroup.userData.roomId;
+    this.selectedIndex = meshGroup.userData.furnitureIndex;
+
+    this._addOutline(meshGroup);
+
+    if (this.mode === 'view') {
+      this.mode = 'select';
+    }
+
+    this._emit('select', {
+      roomId: this.selectedRoomId,
+      index: this.selectedIndex,
+      catalogId: meshGroup.userData.catalogId,
+      itemName: meshGroup.userData.itemName,
+      mesh: meshGroup
+    });
+  }
+
+  clearSelection() {
+    if (!this.selectedObject) return;
+    this._removeOutline();
+    const prev = {
+      roomId: this.selectedRoomId,
+      index: this.selectedIndex
+    };
+    this.selectedObject = null;
+    this.selectedRoomId = null;
+    this.selectedIndex = -1;
+    this._emit('deselect', prev);
+  }
+
+  // ---- Keyboard shortcuts ----
+
+  _onKeyDown(event) {
+    // Don't intercept when typing in an input
+    if (event.target.tagName === 'INPUT' || event.target.tagName === 'TEXTAREA') return;
+
+    // Ctrl+Z / Cmd+Z — undo
+    if ((event.ctrlKey || event.metaKey) && !event.shiftKey && event.key === 'z') {
+      event.preventDefault();
+      this.state.undo();
+      return;
+    }
+
+    // Ctrl+Shift+Z / Cmd+Shift+Z — redo
+    if ((event.ctrlKey || event.metaKey) && event.shiftKey && event.key === 'Z') {
+      event.preventDefault();
+      this.state.redo();
+      return;
+    }
+
+    // Ctrl+Y — redo (alternative)
+    if ((event.ctrlKey || event.metaKey) && event.key === 'y') {
+      event.preventDefault();
+      this.state.redo();
+      return;
+    }
+
+    // Escape — deselect / return to view mode
+    if (event.key === 'Escape') {
+      this.clearSelection();
+      this.setMode('view');
+      return;
+    }
+
+    // Following shortcuts require a selection
+    if (!this.selectedObject) return;
+
+    // Delete / Backspace — remove selected furniture
+    if (event.key === 'Delete' || event.key === 'Backspace') {
+      event.preventDefault();
+      this._deleteSelected();
+      return;
+    }
+
+    // R — rotate 90° clockwise
+    if (event.key === 'r' || event.key === 'R') {
+      const delta = event.shiftKey ? 90 : -90;
+      const item = this.state.getFurniture(this.selectedRoomId, this.selectedIndex);
+      if (item) {
+        const newRotation = ((item.rotation || 0) + delta + 360) % 360;
+        this.state.rotateFurniture(this.selectedRoomId, this.selectedIndex, newRotation);
+      }
+      return;
+    }
+  }
+
+  // ---- Event handlers ----
+
+  _onFurnitureClick(event) {
+    const { mesh } = event.detail;
+    if (mesh) {
+      this.select(mesh);
+    }
+  }
+
+  _onRoomClick(_event) {
+    // Clicking a room (not furniture) clears furniture selection
+    if (this.selectedObject) {
+      this.clearSelection();
+    }
+  }
+
+  _onFloorChange(_event) {
+    // Floor switch invalidates selection (meshes are disposed)
+    this.selectedObject = null;
+    this.selectedRoomId = null;
+    this.selectedIndex = -1;
+    this._outlineGroup = null;
+  }
+
+  _onStateChange(type, _detail) {
+    // On undo/redo/load, re-render the floor to reflect new state
+    if (type === 'undo' || type === 'redo' || type === 'design-load') {
+      this.renderer.designData = this.state.design;
+      const wasSelected = this.selectedRoomId;
+      const wasIndex = this.selectedIndex;
+
+      this._outlineGroup = null;
+      this.selectedObject = null;
+
+      this.renderer._clearFloor();
+      const floor = this.renderer.houseData.floors[this.renderer.currentFloor];
+      if (floor) {
+        for (const room of floor.rooms) {
+          this.renderer._renderRoom(room, floor.ceilingHeight);
+        }
+      }
+      this.renderer._placeFurnitureForFloor();
+
+      // Try to re-select the same item after re-render
+      if (wasSelected !== null && wasIndex >= 0) {
+        const mesh = this._findFurnitureMesh(wasSelected, wasIndex);
+        if (mesh) {
+          this.select(mesh);
+        } else {
+          this.selectedRoomId = null;
+          this.selectedIndex = -1;
+          this._emit('deselect', { roomId: wasSelected, index: wasIndex });
+        }
+      }
+    }
+
+    // On individual mutations, update the mesh in place
+    if (type === 'furniture-move' || type === 'furniture-rotate') {
+      this._syncMeshFromState(_detail.roomId, _detail.index);
+    }
+
+    if (type === 'furniture-remove') {
+      // Mesh was already removed by state; re-render the floor
+      this.clearSelection();
+      this.renderer.designData = this.state.design;
+      this.renderer._clearFloor();
+      const floor = this.renderer.houseData.floors[this.renderer.currentFloor];
+      if (floor) {
+        for (const room of floor.rooms) {
+          this.renderer._renderRoom(room, floor.ceilingHeight);
+        }
+      }
+      this.renderer._placeFurnitureForFloor();
+    }
+  }
+
+  // ---- Outline ----
+
+  _addOutline(meshGroup) {
+    this._removeOutline();
+    const outline = new THREE.Group();
+    outline.userData._isOutline = true;
+
+    meshGroup.traverse(child => {
+      if (child.isMesh && child.geometry) {
+        const clone = new THREE.Mesh(child.geometry, this._outlineMaterial);
+        // Copy the child's local transform relative to the group
+        clone.position.copy(child.position);
+        clone.rotation.copy(child.rotation);
+        clone.scale.copy(child.scale).multiplyScalar(1.04);
+        outline.add(clone);
+      }
+    });
+
+    meshGroup.add(outline);
+    this._outlineGroup = outline;
+  }
+
+  _removeOutline() {
+    if (this._outlineGroup && this._outlineGroup.parent) {
+      this._outlineGroup.parent.remove(this._outlineGroup);
+    }
+    this._outlineGroup = null;
+  }
+
+  // ---- Helpers ----
+
+  _deleteSelected() {
+    if (!this.selectedObject || this.selectedRoomId === null || this.selectedIndex < 0) return;
+    const roomId = this.selectedRoomId;
+    const index = this.selectedIndex;
+    this.clearSelection();
+    this.state.removeFurniture(roomId, index);
+  }
+
+  _findFurnitureMesh(roomId, index) {
+    for (const mesh of this.renderer.furnitureMeshes.values()) {
+      if (mesh.userData.roomId === roomId && mesh.userData.furnitureIndex === index) {
+        return mesh;
+      }
+    }
+    return null;
+  }
+
+  _syncMeshFromState(roomId, index) {
+    const item = this.state.getFurniture(roomId, index);
+    const mesh = this._findFurnitureMesh(roomId, index);
+    if (!item || !mesh) return;
+
+    // Get room position offset
+    const floor = this.renderer.houseData.floors[this.renderer.currentFloor];
+    const room = floor?.rooms.find(r => r.id === roomId);
+    if (!room) return;
+
+    const rx = room.position.x + item.position.x;
+    const rz = room.position.y + item.position.z;
+    const ry = item.wallMounted ? (item.position.y ?? 0) : 0;
+    mesh.position.set(rx, ry, rz);
+    mesh.rotation.y = -(item.rotation * Math.PI) / 180;
+  }
+
+  // ---- Observer pattern ----
+
+  /**
+   * Listen for interaction events.
+   * Types: select, deselect, modechange
+   * Returns unsubscribe function.
+   */
+  onChange(listener) {
+    this._listeners.add(listener);
+    return () => this._listeners.delete(listener);
+  }
+
+  _emit(type, detail) {
+    for (const fn of this._listeners) {
+      try {
+        fn(type, detail);
+      } catch (err) {
+        console.error('InteractionManager listener error:', err);
+      }
+    }
+  }
+
+  // ---- Cleanup ----
+
+  dispose() {
+    this.renderer.container.removeEventListener('furnitureclick', this._onFurnitureClick);
+    this.renderer.container.removeEventListener('roomclick', this._onRoomClick);
+    this.renderer.container.removeEventListener('floorchange', this._onFloorChange);
+    window.removeEventListener('keydown', this._onKeyDown);
+    this._unsubState();
+    this._removeOutline();
+    this._outlineMaterial.dispose();
+    this._listeners.clear();
+  }
+}
diff --git a/src/renderer.js b/src/renderer.js
index 2876f09..e68089d 100644
--- a/src/renderer.js
+++ b/src/renderer.js
@@ -575,6 +575,7 @@ export class HouseRenderer {
           isFurniture: true,
           catalogId: placement.catalogId,
           roomId: roomDesign.roomId,
+          furnitureIndex: i,
           itemName: catalogItem.name,
           wallMounted: !!placement.wallMounted
         };