diff --git a/frontend/src/plugins/builtin/core-modify/index.ts b/frontend/src/plugins/builtin/core-modify/index.ts
index 9ded147..ad5d68a 100644
--- a/frontend/src/plugins/builtin/core-modify/index.ts
+++ b/frontend/src/plugins/builtin/core-modify/index.ts
@@ -31,8 +31,57 @@ const uid = (prefix: string): string =>
   `${prefix}_${Date.now().toString(36)}_${Math.random().toString(36).slice(2, 9)}`;
 
 // ─────────────────────────────────────────────────────────────
-// select (Task A3 – Pilot)
+// select (Task A3 – Pilot) + Handle-Drag (Task C3fin interaktiv)
 // ─────────────────────────────────────────────────────────────
+/** Handle-Drag-Sitzung: aktives Element + gegenüberliegende Ecke. */
+let handleDrag: {
+  el: CADElement;
+  anchorCorner: Pt;
+  handleIndex: number;
+} | null = null;
+
+/** Prüft, ob (wx,wy) eine BBox-Ecke des Elements trifft (Toleranz tol). */
+function hitHandle(
+  el: CADElement,
+  wx: number,
+  wy: number,
+  tol: number,
+): { handleIndex: number; anchorCorner: Pt } | null {
+  const props = el.properties as Record<string, unknown>;
+  let minX: number, minY: number, maxX: number, maxY: number;
+  if (
+    props.x1 !== undefined && props.y1 !== undefined &&
+    props.x2 !== undefined && props.y2 !== undefined
+  ) {
+    minX = Math.min(props.x1 as number, props.x2 as number);
+    minY = Math.min(props.y1 as number, props.y2 as number);
+    maxX = Math.max(props.x1 as number, props.x2 as number);
+    maxY = Math.max(props.y1 as number, props.y2 as number);
+  } else {
+    minX = el.x - el.width / 2;
+    minY = el.y - el.height / 2;
+    maxX = el.x + el.width / 2;
+    maxY = el.y + el.height / 2;
+  }
+  const corners: Array<{ x: number; y: number }> = [
+    { x: minX, y: minY },
+    { x: maxX, y: minY },
+    { x: maxX, y: maxY },
+    { x: minX, y: maxY },
+  ];
+  for (let i = 0; i < corners.length; i++) {
+    if (
+      Math.abs(wx - corners[i].x) <= tol &&
+      Math.abs(wy - corners[i].y) <= tol
+    ) {
+      // Gegenüberliegende Ecke = Anker (bleibt fix beim Skalieren)
+      const anchor = corners[(i + 2) % 4];
+      return { handleIndex: i, anchorCorner: anchor };
+    }
+  }
+  return null;
+}
+
 export const selectTool: ToolExtensionV2 = {
   manifest: {
     id: 'select',
@@ -46,10 +95,28 @@ export const selectTool: ToolExtensionV2 = {
   handlers: {
     down(e, ctx) {
       const bridge = (ctx as FullToolContext).selection;
+      const c = ctx as FullToolContext;
       if (!bridge) return;
       const additive = e.shift;
       const subtractive = e.ctrl;
       const hit = bridge.hitTest(e.world.x, e.world.y, 5);
+
+      // ── Handle-Drag-Start (Task C3fin interaktiv) ──
+      // Wenn bereits Elemente selektiert sind und der Klick auf eine Ecke
+      // eines davon trifft → Handle-Drag starten statt neu zu wählen.
+      if (!additive && !subtractive && bridge.getIds().length > 0 && c.doc) {
+        for (const id of bridge.getIds()) {
+          const el = c.doc.getElement(id);
+          if (!el) continue;
+          const h = hitHandle(el, e.world.x, e.world.y, 8);
+          if (h) {
+            handleDrag = { el, anchorCorner: h.anchorCorner, handleIndex: h.handleIndex };
+            ctx.setStatus(`Handle ${h.handleIndex + 1} — skalieren durch Ziehen`);
+            return;
+          }
+        }
+      }
+
       if (!hit) {
         if (!additive && !subtractive) bridge.setIds([]);
         return;
@@ -64,6 +131,101 @@ export const selectTool: ToolExtensionV2 = {
       bridge.setIds(Array.from(ids));
       ctx.setStatus(`Selektion: ${ids.size} Element(e)`);
     },
+
+    move(e, ctx) {
+      // Live-Skalierung während Handle-Drag:
+      if (!handleDrag) return;
+      const c = ctx as FullToolContext;
+      if (!c.doc) return;
+      const el = c.doc.getElement(handleDrag.el.id);
+      if (!el) return;
+      const props = el.properties as Record<string, unknown>;
+      // BBox aus Element abrufen (mit aktuellen Koordinaten):
+      let minX: number, minY: number, maxX: number, maxY: number;
+      if (
+        props.x1 !== undefined && props.y1 !== undefined &&
+        props.x2 !== undefined && props.y2 !== undefined
+      ) {
+        minX = Math.min(props.x1 as number, props.x2 as number);
+        minY = Math.min(props.y1 as number, props.y2 as number);
+        maxX = Math.max(props.x1 as number, props.x2 as number);
+        maxY = Math.max(props.y1 as number, props.y2 as number);
+      } else {
+        minX = el.x - el.width / 2;
+        minY = el.y - el.height / 2;
+        maxX = el.x + el.width / 2;
+        maxY = el.y + el.height / 2;
+      }
+      // Neue BBox = Anker fix, gezogene Ecke = Maus:
+      const anchor = handleDrag.anchorCorner;
+      const newMinX = Math.min(anchor.x, e.world.x);
+      const newMinY = Math.min(anchor.y, e.world.y);
+      const newMaxX = Math.max(anchor.x, e.world.x);
+      const newMaxY = Math.max(anchor.y, e.world.y);
+      // Preview-Linie von Anker zur Maus (vereinfachtes Feedback):
+      c.setPreview?.({
+        ...el,
+        x: (newMinX + newMaxX) / 2,
+        y: (newMinY + newMaxY) / 2,
+        width: newMaxX - newMinX,
+        height: newMaxY - newMinY,
+      } as CADElement);
+      void minX; void minY; void maxX; void maxY;
+    },
+
+    up(e, ctx) {
+      if (!handleDrag) return;
+      const c = ctx as FullToolContext;
+      if (!c.doc) { handleDrag = null; return; }
+      const el = c.doc.getElement(handleDrag.el.id);
+      const anchor = handleDrag.anchorCorner;
+      if (!el) { handleDrag = null; return; }
+      const props = el.properties as Record<string, unknown>;
+      // Neue BBox berechnen:
+      const newMinX = Math.min(anchor.x, e.world.x);
+      const newMinY = Math.min(anchor.y, e.world.y);
+      const newMaxX = Math.max(anchor.x, e.world.x);
+      const newMaxY = Math.max(anchor.y, e.world.y);
+      const newW = newMaxX - newMinX;
+      const newH = newMaxY - newMinY;
+      const oldW = el.width || 1;
+      const oldH = el.height || 1;
+      const scaleX = oldW !== 0 ? newW / oldW : 1;
+      const scaleY = oldH !== 0 ? newH / oldH : 1;
+      // Neues Zentrum:
+      const newCx = (newMinX + newMaxX) / 2;
+      const newCy = (newMinY + newMaxY) / 2;
+
+      c.doc.transact(() => {
+        // Element in neuer BBox skalieren (shallow properties überschrieben):
+        const newProps = { ...(el.properties as Record<string, unknown>) };
+        // Für line: Koordinaten skalieren relativ zur neuen BBox
+        if (
+          newProps.x1 !== undefined && newProps.y1 !== undefined &&
+          newProps.x2 !== undefined && newProps.y2 !== undefined
+        ) {
+          newProps.x1 = newMinX + ((newProps.x1 as number) - (el.x - el.width / 2)) * scaleX;
+          newProps.y1 = newMinY + ((newProps.y1 as number) - (el.y - el.height / 2)) * scaleY;
+          newProps.x2 = newMinX + ((newProps.x2 as number) - (el.x - el.width / 2)) * scaleX;
+          newProps.y2 = newMinY + ((newProps.y2 as number) - (el.y - el.height / 2)) * scaleY;
+        }
+        c.doc!.updateElement(el.id, {
+          x: newCx,
+          y: newCy,
+          width: newW,
+          height: newH,
+          properties: newProps,
+        });
+      });
+      ctx.setStatus(`Skaliert auf ${newW.toFixed(0)}×${newH.toFixed(0)}`);
+      handleDrag = null;
+      ctx.setPreview?.(null);
+    },
+
+    cancel(ctx) {
+      handleDrag = null;
+      ctx.setPreview?.(null);
+    },
   },
 };
 
diff --git a/frontend/tests/pilotTools.test.ts b/frontend/tests/pilotTools.test.ts
index 60fc74c..f5e3ff8 100644
--- a/frontend/tests/pilotTools.test.ts
+++ b/frontend/tests/pilotTools.test.ts
@@ -860,3 +860,65 @@ describe('D-Ext: array-polar tool', () => {
     expect(doc.getAllElements().length).toBe(1);
   });
 });
+
+describe('C3fin interaktiv: handle-drag on select tool', () => {
+  function makeRect(id: string, x: number, y: number, w: number, h: number): CADElement {
+    return {
+      id, type: 'rect', layerId: 'l',
+      x: x + w / 2, y: y + h / 2,
+      width: w, height: h,
+      properties: { fill: '#abc' },
+    } as unknown as CADElement;
+  }
+
+  it('down auf Handle startet Drag, move skaliert, up committet', () => {
+    const { ydoc } = createInMemoryDoc();
+    const doc = new CADDocument(ydoc);
+    // Rect: (0,0) bis (50,50)
+    doc.addElement(makeRect('r1', 0, 0, 50, 50));
+    let selIds: string[] = ['r1'];
+    const bridge = {
+      getIds: () => selIds,
+      setIds: (ids: string[]) => { selIds = ids; },
+      hitTest: () => null,
+    };
+    const ctx = makeCtx({ doc, selection: bridge });
+    const select = coreModifyPlugin.tools!.find((t) => t.manifest.id === 'select')!;
+
+    // down auf Handle der oberen linken Ecke (0,0):
+    select.handlers.down!(pe(0, 0), ctx);
+    // move zu neuem Punkt (-20, -20):
+    select.handlers.move!(pe(-20, -20), ctx);
+    // up → Commit (Skalierung auf neue BBox von (-20,-20) bis (50,50)):
+    select.handlers.up!(pe(-20, -20), ctx);
+
+    const updated = doc.getElement('r1')!;
+    // Neue BBox: 70×70 statt 50×50:
+    expect(updated.width).toBe(70);
+    expect(updated.height).toBe(70);
+    expect(doc.undo()).toBe(true); // Skalierung ist undo-bar
+    expect(doc.getElement('r1')!.width).toBe(50);
+  });
+
+  it('down auf NICHT-Handle startet normale Selektion (kein Drag)', () => {
+    const { ydoc } = createInMemoryDoc();
+    const doc = new CADDocument(ydoc);
+    doc.addElement(makeRect('r2', 0, 0, 50, 50));
+    doc.addElement(makeRect('r3', 200, 200, 30, 30));
+    let selIds: string[] = ['r2'];
+    const bridge = {
+      getIds: () => selIds,
+      setIds: (ids: string[]) => { selIds = ids; },
+      // Klick bei (210,210) trifft r3:
+      hitTest: () => doc.getElement('r3')!,
+    };
+    const ctx = makeCtx({ doc, selection: bridge });
+    const select = coreModifyPlugin.tools!.find((t) => t.manifest.id === 'select')!;
+
+    // Klick weit weg von Handles von r2 (r2-Ecken sind 0/50):
+    select.handlers.down!(pe(210, 210), ctx);
+
+    // Normal-Selektion: r3 ist jetzt alleine selektiert (kein Drag gestartet):
+    expect(selIds).toEqual(['r3']);
+  });
+});