diff --git a/server/src/__tests__/plugin-orchestration-apis.test.ts b/server/src/__tests__/plugin-orchestration-apis.test.ts
index 968c01ccfe2..8712d8ab5b3 100644
--- a/server/src/__tests__/plugin-orchestration-apis.test.ts
+++ b/server/src/__tests__/plugin-orchestration-apis.test.ts
@@ -1036,6 +1036,42 @@ describeEmbeddedPostgres("plugin orchestration APIs", () => {
     });
   });
 
+  it("respondInteraction rejects duplicate checkbox option ids at the plugin boundary", async () => {
+    const { companyId } = await seedCompanyAndAgent();
+    const operatorUserId = randomUUID();
+    await db.insert(companyMemberships).values({
+      companyId, principalType: "user", principalId: operatorUserId, status: "active", membershipRole: "operator",
+    });
+    const issueId = randomUUID();
+    await db.insert(issues).values({
+      id: issueId, companyId, title: "Choose campaigns", status: "in_review", priority: "medium",
+    });
+    const interactionId = await seedInteraction(companyId, issueId, {
+      kind: "request_checkbox_confirmation",
+      payload: {
+        version: 1,
+        prompt: "Which spikes should become campaigns?",
+        options: [{ id: "spike-a", label: "Spike A" }],
+        defaultSelectedOptionIds: [],
+        minSelected: 0,
+        maxSelected: 1,
+      } as never,
+    });
+    const services = buildHostServices(db, "plugin-record-id", "paperclip.gateway", createEventBusStub());
+
+    await expect(services.issues.respondInteraction({
+      issueId,
+      interactionId,
+      companyId,
+      action: "accept",
+      actorUserId: operatorUserId,
+      selectedOptionIds: ["spike-a", "spike-a"],
+    })).rejects.toThrow("selectedOptionIds must be unique");
+
+    const [row] = await db.select().from(issueThreadInteractions).where(eq(issueThreadInteractions.id, interactionId));
+    expect(row?.status).toBe("pending");
+  });
+
   it("respondInteraction converges (applied:false) when the interaction is already resolved", async () => {
     const { companyId, agentId } = await seedCompanyAndAgent();
     const humanUserId = randomUUID();
diff --git a/server/src/services/plugin-host-services.ts b/server/src/services/plugin-host-services.ts
index b1753cfd87f..1d219291c56 100644
--- a/server/src/services/plugin-host-services.ts
+++ b/server/src/services/plugin-host-services.ts
@@ -28,7 +28,7 @@ import type {
   PluginExecutionWorkspaceMetadata,
 } from "@paperclipai/plugin-sdk";
 import type { CreateIssueThreadInteraction, InviteJoinType, IssueDocumentSummary, PermissionKey, PrincipalType } from "@paperclipai/shared";
-import { pluginOperationIssueOriginKind } from "@paperclipai/shared";
+import { acceptIssueThreadInteractionSchema, pluginOperationIssueOriginKind } from "@paperclipai/shared";
 import { companyService } from "./companies.js";
 import { agentService } from "./agents.js";
 import { projectService } from "./projects.js";
@@ -2286,12 +2286,13 @@ export function buildHostServices(
           status: issue.status,
         };
         if (params.action === "accept") {
+          const acceptInput = acceptIssueThreadInteractionSchema.parse({
+            selectedOptionIds: params.selectedOptionIds,
+          });
           const result = await interactions.acceptInteraction(
             { id: issue.id, companyId, projectId: issue.projectId ?? null, goalId: issue.goalId ?? null },
             params.interactionId,
-            params.selectedOptionIds === undefined
-              ? {}
-              : { selectedOptionIds: params.selectedOptionIds },
+            acceptInput,
             actor,
           );
           resolved = result.interaction as typeof current;