fix(update): keep migrated keys when option shape changes

src/update.ts

@@ -181,7 +181,12 @@ function collectObjectOverrides(prev: Signature, next: Signature): Map<string, n
 
   const missingObjects = diffKeys(prev.objects, next.objects);
   for (let i = 0; i < missingObjects.length; i++) {
-    overrides.set(missingObjects[i], null);
+    const key = missingObjects[i];
+    const movedToArray = next.arrays[key] !== undefined;
+    const movedToScalar = next.scalars.includes(key);
+    if (!movedToArray && !movedToScalar) {
+      overrides.set(key, null);
+    }
   }
 
   return overrides;

tests/update.node.test.ts

@@ -418,6 +418,67 @@ describe("smart-update", () => {
         expect(result.plan.notMerge).toBe(false);
         expect(result.plan.replaceMerge).toBeUndefined();
       });
+
+      it("handles single-object series shape without array replacement planning", () => {
+        const base: EChartsOption = {
+          series: {
+            type: "line",
+            data: [1, 2, 3],
+          } as unknown as EChartsOption["series"],
+        };
+
+        const update: EChartsOption = {
+          series: {
+            type: "line",
+            data: [2, 3, 4],
+          } as unknown as EChartsOption["series"],
+        };
+
+        const result = planUpdate(buildSignature(base), update);
+
+        expect(result.plan.notMerge).toBe(false);
+        expect(result.plan.replaceMerge).toBeUndefined();
+        expect(result.option.series).toEqual(update.series);
+      });
+
+      it("keeps next series array when migrating from single-object series", () => {
+        const base: EChartsOption = {
+          series: {
+            type: "bar",
+            data: [10, 20],
+          } as unknown as EChartsOption["series"],
+        };
+
+        const update: EChartsOption = {
+          series: [{ id: "latte", type: "bar", data: [12, 24] }],
+        };
+
+        const result = planUpdate(buildSignature(base), update);
+
+        expect(result.plan.notMerge).toBe(false);
+        expect(result.option.series).toEqual(update.series);
+        expect(result.option.series).not.toBeNull();
+      });
+
+      it("prioritizes notMerge when scalar removal happens with array shrink", () => {
+        const base: EChartsOption = {
+          color: "#000",
+          series: [
+            { id: "a", type: "line", data: [1] },
+            { id: "b", type: "line", data: [2] },
+          ],
+        };
+
+        const update: EChartsOption = {
+          series: [{ id: "a", type: "line", data: [3] }],
+        };
+
+        const result = planUpdate(buildSignature(base), update);
+
+        expect(result.plan.notMerge).toBe(true);
+        expect(result.plan.replaceMerge).toBeUndefined();
+        expect(result.option.series).toEqual(update.series);
+      });
     });
   });
 });