diff --git a/frontend/src/plugins/builtin/core-modify/index.ts b/frontend/src/plugins/builtin/core-modify/index.ts
index 30e463c..9ded147 100644
--- a/frontend/src/plugins/builtin/core-modify/index.ts
+++ b/frontend/src/plugins/builtin/core-modify/index.ts
@@ -388,6 +388,213 @@ function makeArrayTool(mode: 'array-rect' | 'array-polar'): ToolExtensionV2 {
 export const arrayRectTool: ToolExtensionV2 = makeArrayTool('array-rect');
 export const arrayPolarTool: ToolExtensionV2 = makeArrayTool('array-polar');
 
+// ─────────────────────────────────────────────────────────────
+// Chamfer (Task D-Ext): schneidet zwei sich schneidende Linien an einer
+// festen Distanz vom Schnittpunkt und verbindet die Enden mit einer
+// geraden Fase. Legacy nutzt trimElement + Verbindungslinie.
+// Klick 1: erste Linie, Klick 2: zweite Linie → 3 Elemente (2 gekürzt + 1 Fase).
+// ─────────────────────────────────────────────────────────────
+let chamferFirst: CADElement | null = null;
+
+export const chamferTool: ToolExtensionV2 = {
+  manifest: {
+    id: 'chamfer', label: 'Chamfer', icon: '\u25e4', ribbonTab: 'canvas', tags: ['pro'],
+    description: 'Zwei Linien anklicken — Fase wird eingefügt',
+  },
+  optionsSchema: [
+    { key: 'chamferDist', label: 'Fase-Distanz', type: 'number', min: 1, max: 100 },
+  ],
+  handlers: {
+    down(e, ctx) {
+      const c = ctx as FullToolContext;
+      if (!c.doc || !c.selection) return;
+      const hit = c.selection.hitTest(e.world.x, e.world.y, 5);
+      if (!hit) return;
+      if (!chamferFirst) {
+        chamferFirst = hit;
+        ctx.setStatus('Chamfer: zweite Linie wählen');
+        return;
+      }
+      const dist = (c.options.chamferDist as number | undefined) ?? 10;
+      // Beide Linien auf dist vom Schnittpunkt kürzen:
+      const t1 = trimElement(chamferFirst, hit);
+      const t2 = trimElement(hit, chamferFirst);
+      if (!t1 || !t2) {
+        ctx.setStatus('Chamfer: kein Schnittpunkt');
+        chamferFirst = null;
+        return;
+      }
+      // Endpunkte nahe am Schnittpunkt holen und um dist zurücksetzen:
+      const props1 = t1.properties as { x1?: number; y1?: number; x2?: number; y2?: number };
+      const props2 = t2.properties as { x1?: number; y1?: number; x2?: number; y2?: number };
+      if (props1.x1 === undefined || props1.y1 === undefined || props1.x2 === undefined || props1.y2 === undefined ||
+          props2.x1 === undefined || props2.y1 === undefined || props2.x2 === undefined || props2.y2 === undefined) {
+        chamferFirst = null;
+        return;
+      }
+      // Nahe Enden (Schnittpunkt-Seite) identifizieren via Schnittpunkt:
+      const isectPt = findIsectPoint(chamferFirst, hit);
+      if (!isectPt) { chamferFirst = null; return; }
+      const near1 = nearEnd(props1 as { x1: number; y1: number; x2: number; y2: number }, isectPt);
+      const near2 = nearEnd(props2 as { x1: number; y1: number; x2: number; y2: number }, isectPt);
+      // Kürze nahe Enden auf dist vom Schnittpunkt:
+      const shrink1 = shrinkTowards(props1 as { x1: number; y1: number; x2: number; y2: number }, near1, isectPt, dist);
+      const shrink2 = shrinkTowards(props2 as { x1: number; y1: number; x2: number; y2: number }, near2, isectPt, dist);
+      // Fase: Linie zwischen den neuen Enden:
+      const chamferLine: CADElement = {
+        ...chamferFirst,
+        id: uid('cham'),
+        type: 'line',
+        x: (shrink1.near.x + shrink2.near.x) / 2,
+        y: (shrink1.near.y + shrink2.near.y) / 2,
+        width: Math.abs(shrink2.near.x - shrink1.near.x),
+        height: Math.abs(shrink2.near.y - shrink1.near.y),
+        properties: {
+          x1: shrink1.near.x, y1: shrink1.near.y,
+          x2: shrink2.near.x, y2: shrink2.near.y,
+          stroke: '#e0e0e0', strokeWidth: 1,
+        },
+      };
+      c.doc.transact(() => {
+        c.doc!.updateElement(chamferFirst!.id, {
+          x: shrink1.cx, y: shrink1.cy,
+          width: Math.abs(props1.x2! - props1.x1!),
+          height: Math.abs(props1.y2! - props1.y1!),
+          properties: props1,
+        });
+        c.doc!.updateElement(hit.id, {
+          x: shrink2.cx, y: shrink2.cy,
+          width: Math.abs(props2.x2! - props2.x1!),
+          height: Math.abs(props2.y2! - props2.y1!),
+          properties: props2,
+        });
+        c.doc!.addElement(chamferLine);
+      });
+      ctx.setStatus('Chamfer erstellt');
+      chamferFirst = null;
+    },
+    cancel(ctx) {
+      chamferFirst = null;
+      ctx.setStatus('Chamfer abgebrochen');
+    },
+  },
+};
+
+function findIsectPoint(a: CADElement, b: CADElement): Pt | null {
+  const pa = a.properties as { x1?: number; y1?: number; x2?: number; y2?: number };
+  const pb = b.properties as { x1?: number; y1?: number; x2?: number; y2?: number };
+  if (pa.x1 === undefined || pb.x1 === undefined) return null;
+  const denom = (pa.x1! - pa.x2!) * (pb.y1! - pb.y2!) - (pa.y1! - pa.y2!) * (pb.x1! - pb.x2!);
+  if (Math.abs(denom) < 1e-10) return null;
+  const t = ((pa.x1! - pb.x1!) * (pb.y1! - pb.y2!) - (pa.y1! - pb.y1!) * (pb.x1! - pb.x2!)) / denom;
+  return { x: pa.x1! + t * (pa.x2! - pa.x1!), y: pa.y1! + t * (pa.y2! - pa.y1!) };
+}
+
+function nearEnd(props: { x1: number; y1: number; x2: number; y2: number }, pt: Pt): 'start' | 'end' {
+  const d1 = Math.hypot(props.x1 - pt.x, props.y1 - pt.y);
+  const d2 = Math.hypot(props.x2 - pt.x, props.y2 - pt.y);
+  return d1 < d2 ? 'start' : 'end';
+}
+
+function shrinkTowards(
+  props: { x1: number; y1: number; x2: number; y2: number },
+  near: 'start' | 'end',
+  isectPt: Pt,
+  dist: number,
+): { near: Pt; cx: number; cy: number } {
+  if (near === 'start') {
+    const len = Math.hypot(props.x2 - props.x1, props.y2 - props.y1);
+    if (len === 0) return { near: { x: props.x1, y: props.y1 }, cx: props.x1, cy: props.y1 };
+    const ratio = Math.min(dist / len, 1);
+    const nx = props.x1 + (props.x2 - props.x1) * ratio;
+    const ny = props.y1 + (props.y2 - props.y1) * ratio;
+    return { near: { x: nx, y: ny }, cx: (nx + props.x2) / 2, cy: (ny + props.y2) / 2 };
+  }
+  const len = Math.hypot(props.x2 - props.x1, props.y2 - props.y1);
+  if (len === 0) return { near: { x: props.x2, y: props.y2 }, cx: props.x2, cy: props.y2 };
+  const ratio = Math.min(dist / len, 1);
+  const nx = props.x2 + (props.x1 - props.x2) * ratio;
+  const ny = props.y2 + (props.y1 - props.y2) * ratio;
+  return { near: { x: nx, y: ny }, cx: (nx + props.x1) / 2, cy: (ny + props.y1) / 2 };
+}
+
+// ─────────────────────────────────────────────────────────────
+// Lengthen (Task D-Ext): verlängert/verkürzt eine Linie am geklickten
+// Ende um einen Delta-Wert. Klick 1: Linie, Klick 2: Seite.
+// ─────────────────────────────────────────────────────────────
+let lengthenEl: CADElement | null = null;
+
+export const lengthenTool: ToolExtensionV2 = {
+  manifest: {
+    id: 'lengthen', label: 'Lengthen', icon: '\u2194', ribbonTab: 'canvas', tags: ['pro'],
+    description: 'Linie anklicken, dann Delta-Ziel klicken (Options: lengthenDelta)',
+  },
+  optionsSchema: [
+    { key: 'lengthenDelta', label: 'Delta', type: 'number' },
+  ],
+  handlers: {
+    down(e, ctx) {
+      const c = ctx as FullToolContext;
+      if (!c.doc || !c.selection) return;
+      if (!lengthenEl) {
+        const hit = c.selection.hitTest(e.world.x, e.world.y, 5);
+        if (!hit || hit.type !== 'line') {
+          ctx.setStatus('Lengthen: nur Linien');
+          return;
+        }
+        lengthenEl = hit;
+        ctx.setStatus('Lengthen: Klick in Verlängerungsrichtung');
+        return;
+      }
+      const el = c.doc.getElement(lengthenEl.id);
+      if (!el) { lengthenEl = null; return; }
+      const props = el.properties as { x1?: number; y1?: number; x2?: number; y2?: number };
+      if (props.x1 === undefined || props.y1 === undefined || props.x2 === undefined || props.y2 === undefined) {
+        lengthenEl = null;
+        return;
+      }
+      const delta = (c.options.lengthenDelta as number | undefined) ?? 10;
+      // Wähle das Ende, das dem Klick am nächsten ist:
+      const dStart = Math.hypot(e.world.x - (props.x1 as number), e.world.y - (props.y1 as number));
+      const dEnd = Math.hypot(e.world.x - (props.x2 as number), e.world.y - (props.y2 as number));
+      const nearIsStart = dStart < dEnd;
+      // Richtungsvektor (vom fernen Ende zum nahen Ende):
+      const dirX = nearIsStart ? (props.x1! - props.x2!) : (props.x2! - props.x1!);
+      const dirY = nearIsStart ? (props.y1! - props.y2!) : (props.y2! - props.y1!);
+      const len = Math.hypot(dirX, dirY);
+      if (len === 0) { lengthenEl = null; return; }
+      const ux = dirX / len;
+      const uy = dirY / len;
+      if (nearIsStart) {
+        props.x1 = (props.x1 as number) + ux * delta;
+        props.y1 = (props.y1 as number) + uy * delta;
+      } else {
+        props.x2 = (props.x2 as number) + ux * delta;
+        props.y2 = (props.y2 as number) + uy * delta;
+      }
+      const nx1 = props.x1 as number;
+      const ny1 = props.y1 as number;
+      const nx2 = props.x2 as number;
+      const ny2 = props.y2 as number;
+      c.doc.transact(() => {
+        c.doc!.updateElement(el.id, {
+          x: (nx1 + nx2) / 2,
+          y: (ny1 + ny2) / 2,
+          width: Math.abs(nx2 - nx1),
+          height: Math.abs(ny2 - ny1),
+          properties: props,
+        });
+      });
+      ctx.setStatus(`Lengthen: Linie um ${delta} angepasst`);
+      lengthenEl = null;
+    },
+    cancel(ctx) {
+      lengthenEl = null;
+      ctx.setStatus('Lengthen abgebrochen');
+    },
+  },
+};
+
 // ─────────────────────────────────────────────────────────────
 // Trim / Extend / Fillet (Task A4.10) — baut auf BUG-2-reparierter
 // findIntersection-Geometrie (B2). Legacy-Ablauf:
@@ -581,11 +788,11 @@ export const coreModifyPlugin: PluginV2 = {
   manifest: {
     id: 'core-modify',
     name: 'Bearbeiten (Kern)',
-    version: '1.6.0',
+    version: '1.7.0',
     author: 'web-cad team',
-    description: 'Auswahl, Schraffur, Move/Copy/Rotate/Scale/Mirror/Delete/Offset/Trim/Extend/Fillet/Arrays (V2).',
+    description: 'Auswahl, Schraffur, Move/Copy/Rotate/Scale/Mirror/Delete/Offset/Trim/Extend/Fillet/Arrays/Chamfer/Lengthen (V2).',
     category: 'tools',
     enabledByDefault: true,
   },
-  tools: [selectTool, hatchTool, moveTool, copyTool, rotateTool, scaleTool, mirrorTool, deleteTool, offsetTool, trimTool, extendTool, filletTool, arrayRectTool, arrayPolarTool],
+  tools: [selectTool, hatchTool, moveTool, copyTool, rotateTool, scaleTool, mirrorTool, deleteTool, offsetTool, trimTool, extendTool, filletTool, arrayRectTool, arrayPolarTool, chamferTool, lengthenTool],
 };