diff --git a/src/db/repositories/external-object-assignment-plan-project-command.repository.ts b/src/db/repositories/external-object-assignment-plan-project-command.repository.ts
index d34c4c0..cce586b 100644
--- a/src/db/repositories/external-object-assignment-plan-project-command.repository.ts
+++ b/src/db/repositories/external-object-assignment-plan-project-command.repository.ts
@@ -164,6 +164,14 @@ export class ExternalObjectAssignmentPlanProjectCommandRepository
       command.payload.objects,
       "External object changed before plan assignment."
     );
+    // A new plan may only link objects present in the latest import; the
+    // generic command route must not bypass the dialog route's rule.
+    if (
+      source === "user" &&
+      command.payload.objects.some(({ expected }) => expected.presenceStatus !== "present")
+    ) {
+      throw new Error("Missing external objects cannot be assigned.");
+    }
 
     for (const circuit of newCircuits) {
       assertEquipmentIdentifierAvailable(
diff --git a/src/shared/validation/external-object-assignment-plan.schemas.ts b/src/shared/validation/external-object-assignment-plan.schemas.ts
index 56cd31e..23aee62 100644
--- a/src/shared/validation/external-object-assignment-plan.schemas.ts
+++ b/src/shared/validation/external-object-assignment-plan.schemas.ts
@@ -1,8 +1,11 @@
 import { z } from "zod";
 import { expectedProjectRevisionSchema } from "./project-command.schemas.js";
 
+// Upper bound for all objects of one plan; the 5,000-object scale test stays
+// well inside it.
+export const maxAssignmentPlanObjects = 10000;
 const idSchema = z.string().min(1).max(200);
-const objectIdsSchema = z.array(idSchema).min(1).max(10000);
+const objectIdsSchema = z.array(idSchema).min(1).max(maxAssignmentPlanObjects);
 const newCircuitKeySchema = z.string().min(1).max(100);
 
 /** Request of the Revit assignment dialog (requirements §11.7). */
@@ -38,7 +41,13 @@ export const applyExternalObjectAssignmentPlanSchema = z
     confirmedConflictObjectIds: z.array(idSchema).max(10000),
     confirmedOverLimitCircuitKeys: z.array(z.string().min(1).max(200)).max(5000),
   })
-  .strict();
+  .strict()
+  .refine(
+    (plan) =>
+      plan.rows.reduce((sum, row) => sum + row.objectIds.length, 0) <=
+      maxAssignmentPlanObjects,
+    { message: `Ein Plan darf höchstens ${maxAssignmentPlanObjects} Revit-Objekte enthalten.`, path: ["rows"] }
+  );
 
 export type ApplyExternalObjectAssignmentPlanInput = z.infer<
   typeof applyExternalObjectAssignmentPlanSchema
diff --git a/tests/external-object-assignment-plan-project-command.repository.test.ts b/tests/external-object-assignment-plan-project-command.repository.test.ts
index 5a4a9c5..2053791 100644
--- a/tests/external-object-assignment-plan-project-command.repository.test.ts
+++ b/tests/external-object-assignment-plan-project-command.repository.test.ts
@@ -215,6 +215,35 @@ describe("external object assignment-plan project command", () => {
     }
   });
 
+  it("rejects user plans for objects missing in the latest import", () => {
+    const context = createFixture();
+    try {
+      context.db.update(externalModelObjects).set({ presenceStatus: "missing" })
+        .where(eq(externalModelObjects.id, "object-b1")).run();
+      const command = createExternalObjectAssignmentPlanProjectCommand(
+        externalObjectApplyAssignmentPlanCommandType,
+        {
+          ...planCommand(context.db).payload,
+          objects: planCommand(context.db).payload.objects.map(({ expected, target }) =>
+            expected.id === "object-b1"
+              ? { expected: { ...expected, presenceStatus: "missing" as const }, target: { ...target, presenceStatus: "missing" as const } }
+              : { expected, target }
+          ),
+        }
+      );
+      const before = readState(context.db);
+      assert.throws(
+        () => new ExternalObjectAssignmentPlanProjectCommandRepository(context.db).execute({
+          projectId: "project-1", expectedRevision: 0, source: "user", command,
+        }),
+        /Missing external objects cannot be assigned/
+      );
+      assert.deepEqual(readState(context.db), before);
+    } finally {
+      context.close();
+    }
+  });
+
   it("refuses undo after a created row was changed", () => {
     const context = createFixture();
     try {
diff --git a/tests/external-object-assignment-plan-route.test.ts b/tests/external-object-assignment-plan-route.test.ts
index eecc1a7..b3916c7 100644
--- a/tests/external-object-assignment-plan-route.test.ts
+++ b/tests/external-object-assignment-plan-route.test.ts
@@ -184,6 +184,14 @@ describe("Revit assignment plan route", () => {
       400
     );
     assert.equal((await call("POST", path, user, { ...plan(circuitListId), rows: [] })).status, 400);
+    const tooManyObjects = Array.from({ length: 10 }, (_, row) => ({
+      kind: "new-row",
+      circuitId: "c",
+      objectIds: Array.from({ length: 1001 }, (_, index) => `o-${row}-${index}`),
+    }));
+    const oversized = await call("POST", path, user, { ...plan(circuitListId), rows: tooManyObjects });
+    assert.equal(oversized.status, 400);
+    assert.match(await oversized.text(), /höchstens 10000 Revit-Objekte/);
   });
 
   it("rejects a circuit list of another project and unknown objects", async () => {