diff --git a/lib/canvas/agent-mutations.ts b/lib/canvas/agent-mutations.ts
index 15fe50083..22f731827 100644
--- a/lib/canvas/agent-mutations.ts
+++ b/lib/canvas/agent-mutations.ts
@@ -433,6 +433,34 @@ function getNodePosition(node: any) {
   };
 }
 
+function removeCanvasNodesAndConnectedEdges(params: {
+  nodes: any[];
+  edges: any[];
+  nodeIds: string[];
+}) {
+  const deleteSet = new Set(params.nodeIds.filter(Boolean));
+  if (deleteSet.size === 0) return [];
+
+  const removedNodeIds = params.nodes
+    .filter((node) => deleteSet.has(node?.id))
+    .map((node) => node.id);
+  if (removedNodeIds.length === 0) return [];
+
+  for (let index = params.nodes.length - 1; index >= 0; index -= 1) {
+    if (deleteSet.has(params.nodes[index]?.id)) {
+      params.nodes.splice(index, 1);
+    }
+  }
+  for (let index = params.edges.length - 1; index >= 0; index -= 1) {
+    const edge = params.edges[index];
+    if (deleteSet.has(edge?.source) || deleteSet.has(edge?.target)) {
+      params.edges.splice(index, 1);
+    }
+  }
+
+  return removedNodeIds;
+}
+
 function isConfirmedHighRiskPlan(plan: CanvasOperationPlan) {
   const metadata = (plan.metadata || {}) as Record<string, unknown>;
   return plan.confirmed === true || metadata.confirmedByUser === true;
@@ -1458,6 +1486,7 @@ function applyOperationToCanvasData(params: {
   if (params.plan.operation === "fill_slot" && !targetSlot) {
     throw new CanvasAgentMutationError("目标 slot 不存在");
   }
+  let replacedSlotNodeIds: string[] = [];
   if (targetSlot && params.plan.operation === "fill_slot") {
     const targetSlotData = (targetSlot.data || {}) as Record<string, unknown>;
     const fillPolicy = normalizeSlotFillPolicy(targetSlotData.fillPolicy);
@@ -1470,13 +1499,28 @@ function applyOperationToCanvasData(params: {
       mediaItems,
     });
 
-    if (fillPolicy === "replace-existing" && filledNodeIds.length > 0) {
+    if (params.baseCanvasWasStale && fillPolicy === "replace-existing") {
       throw new CanvasAgentMutationError(
-        "当前 slot 已有结果，替换已有结果需要用户确认",
+        "画布已更新，替换 slot 前需要刷新并确认",
         409,
-        "CANVAS_AGENT_CONFIRMATION_REQUIRED"
+        "STALE_CANVAS_REVISION"
       );
     }
+
+    if (fillPolicy === "replace-existing" && filledNodeIds.length > 0) {
+      if (!isConfirmedHighRiskPlan(params.plan)) {
+        throw new CanvasAgentMutationError(
+          "当前 slot 已有结果，替换已有结果需要用户确认",
+          409,
+          "CANVAS_AGENT_CONFIRMATION_REQUIRED"
+        );
+      }
+      replacedSlotNodeIds = removeCanvasNodesAndConnectedEdges({
+        nodes,
+        edges,
+        nodeIds: filledNodeIds,
+      });
+    }
     if (fillPolicy === "replace-empty" && filledNodeIds.length > 0) {
       throw new CanvasAgentMutationError(
         "当前 slot 已被填充，请新建 slot 或使用追加版本",
@@ -1484,13 +1528,6 @@ function applyOperationToCanvasData(params: {
         "CANVAS_AGENT_CONFLICT"
       );
     }
-    if (params.baseCanvasWasStale && fillPolicy === "replace-existing") {
-      throw new CanvasAgentMutationError(
-        "画布已更新，替换 slot 前需要刷新并确认",
-        409,
-        "STALE_CANVAS_REVISION"
-      );
-    }
   }
 
   const createdNodeIds: string[] = [];
@@ -1513,6 +1550,17 @@ function applyOperationToCanvasData(params: {
       size: placement.size,
       sourceNodeIds: placement.sourceNodeIds,
     });
+    if (replacedSlotNodeIds.length > 0) {
+      const nodeData = (node.data || {}) as Record<string, any>;
+      (node as any).data = {
+        ...nodeData,
+        metadata: {
+          ...(nodeData.metadata || {}),
+          replacedSlotNodeIds,
+          replacedSlotId: targetSlot?.id,
+        },
+      };
+    }
     nodes.push(node);
     createdNodeIds.push(node.id);
     createdNodeIdsByMediaItemId[placement.item.mediaItemId] = node.id;
@@ -1534,7 +1582,20 @@ function applyOperationToCanvasData(params: {
         ? data.filledNodeIds
         : [];
       data.status = "completed";
-      data.filledNodeIds = Array.from(new Set([...filledNodeIds, node.id]));
+      data.filledNodeIds =
+        replacedSlotNodeIds.length > 0
+          ? Array.from(new Set(createdNodeIds))
+          : Array.from(new Set([...filledNodeIds, node.id]));
+      data.metadata = {
+        ...((data.metadata || {}) as Record<string, unknown>),
+        ...(replacedSlotNodeIds.length > 0
+          ? {
+              replacedSlotNodeIds,
+              replacedByCanvasAgentOperationId: params.plan.operationId,
+              replacedAt: new Date().toISOString(),
+            }
+          : {}),
+      };
       targetSlot.data = data;
       if (!updatedNodeIds.includes(targetSlot.id)) {
         updatedNodeIds.push(targetSlot.id);
diff --git a/tests/routes/canvas-agent-operations.test.ts b/tests/routes/canvas-agent-operations.test.ts
index af0551ee4..5d6f23715 100644
--- a/tests/routes/canvas-agent-operations.test.ts
+++ b/tests/routes/canvas-agent-operations.test.ts
@@ -775,6 +775,124 @@ test.describe("canvas agent operation mutation contract", () => {
     ).toThrow("目标 slot 是图片槽位，不能填充视频结果");
   });
 
+  test("confirms replace-existing slot fills and keeps retries idempotent", () => {
+    const slot = buildAgentSlotNode("slot-replace-existing") as any;
+    slot.data = {
+      ...slot.data,
+      fillPolicy: "replace-existing",
+      filledNodeIds: ["old-slot-result"],
+    };
+    const oldResult = {
+      ...buildImageNode("old-slot-result"),
+      position: { x: 500, y: 120 },
+    };
+    const unrelated = buildImageNode("unrelated-image");
+    const canvasData = {
+      ...getCanvasData([slot, oldResult, unrelated]),
+      edges: [
+        {
+          id: "edge-slot-old-result",
+          source: "slot-replace-existing",
+          target: "old-slot-result",
+          type: "default",
+        },
+      ],
+      selectedNodeIds: ["slot-replace-existing"],
+    };
+    const plan: CanvasOperationPlan = {
+      version: 1,
+      operationId: "op-replace-existing-slot-fill",
+      operation: "fill_slot",
+      projectId,
+      targetSlotId: "slot-replace-existing",
+      mediaItems: [buildMutationMediaItem("media-new-slot-result")],
+    };
+
+    expect(() =>
+      applyCanvasOperationPlanToCanvasData({
+        canvasData,
+        plan,
+      })
+    ).toThrow(/需要用户确认/);
+
+    let staleError: unknown;
+    try {
+      applyCanvasOperationPlanToCanvasData({
+        canvasData,
+        baseCanvasWasStale: true,
+        plan: {
+          ...plan,
+          confirmed: true,
+        },
+      });
+    } catch (error) {
+      staleError = error;
+    }
+
+    expect(staleError).toBeInstanceOf(CanvasAgentMutationError);
+    expect((staleError as CanvasAgentMutationError).code).toBe(
+      "STALE_CANVAS_REVISION"
+    );
+
+    const replaced = applyCanvasOperationPlanToCanvasData({
+      canvasData,
+      plan: {
+        ...plan,
+        confirmed: true,
+        metadata: {
+          confirmedByUser: true,
+        },
+      },
+    });
+    const replacedNodes = getResultNodes(replaced.canvasData);
+    const newNodeId = replaced.createdNodeIds[0];
+
+    expect(replaced.createdNodeIds).toHaveLength(1);
+    expect(replaced.createdNodeIdsByMediaItemId).toEqual({
+      "media-new-slot-result": newNodeId,
+    });
+    expect(replacedNodes.some((node) => node.id === "old-slot-result")).toBe(false);
+    expect(replacedNodes.some((node) => node.id === "unrelated-image")).toBe(true);
+    expect(replacedNodes.find((node) => node.id === "slot-replace-existing"))
+      .toMatchObject({
+        data: {
+          filledNodeIds: [newNodeId],
+          metadata: {
+            replacedSlotNodeIds: ["old-slot-result"],
+            replacedByCanvasAgentOperationId: "op-replace-existing-slot-fill",
+          },
+        },
+      });
+    expect(replacedNodes.find((node) => node.id === newNodeId)).toMatchObject({
+      data: {
+        metadata: {
+          replacedSlotNodeIds: ["old-slot-result"],
+          replacedSlotId: "slot-replace-existing",
+        },
+      },
+    });
+    expect(getResultEdges(replaced.canvasData)).toEqual([
+      expect.objectContaining({
+        source: "slot-replace-existing",
+        target: newNodeId,
+      }),
+    ]);
+
+    const retry = applyCanvasOperationPlanToCanvasData({
+      canvasData: replaced.canvasData,
+      plan: {
+        ...plan,
+        confirmed: true,
+      },
+    });
+
+    expect(retry.createdNodeIds).toEqual(replaced.createdNodeIds);
+    expect(getResultNodes(retry.canvasData)).toHaveLength(replacedNodes.length);
+    expect(
+      getResultNodes(retry.canvasData).filter((node) => node.id === newNodeId)
+    ).toHaveLength(1);
+  });
+
   test("creates append revision nodes without overwriting the source", () => {
     const source = buildImageNode("image-source");
     const result = applyCanvasOperationPlanToCanvasData({