diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f2483bc3..2b9895fb 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -32,3 +32,4 @@ jobs:
       - run: pnpm -C examples/vue-ssr-extra test-e2e
       - run: pnpm -C examples/vue-ssr-extra build
       - run: pnpm -C examples/vue-ssr-extra test-e2e-preview
+      - run: pnpm -C examples/vue-ssr-extra tsc
diff --git a/examples/vue-ssr-extra/src/features/server-action/client.ts b/examples/vue-ssr-extra/src/features/server-action/client.ts
index 4eea3956..b986bdfd 100644
--- a/examples/vue-ssr-extra/src/features/server-action/client.ts
+++ b/examples/vue-ssr-extra/src/features/server-action/client.ts
@@ -1,5 +1,9 @@
 import { tinyassert } from "@hiogawa/utils";
-import { ACTION_PATH, registerServerReference } from "./shared";
+import {
+  ACTION_PATH,
+  registerServerReference,
+  type ServerActionPayload,
+} from "./shared";
 
 export function createServerReference(id: string, name: string) {
   const action = async (...args: unknown[]) => {
@@ -25,7 +29,7 @@ function encodeActionPayload(
     };
   } else {
     return {
-      body: JSON.stringify({ id, name, args }),
+      body: JSON.stringify({ id, name, args } satisfies ServerActionPayload),
       headers: {
         "content-type": "application/json",
       },
diff --git a/examples/vue-ssr-extra/src/features/server-action/server.ts b/examples/vue-ssr-extra/src/features/server-action/server.ts
index 864b8973..91545acf 100644
--- a/examples/vue-ssr-extra/src/features/server-action/server.ts
+++ b/examples/vue-ssr-extra/src/features/server-action/server.ts
@@ -1,5 +1,5 @@
 import { tinyassert } from "@hiogawa/utils";
-import { ACTION_PATH, decodeActionRequest } from "./shared";
+import { ACTION_PATH, type ServerActionPayload } from "./shared";
 
 export async function serverActionHandler({ request }: { request: Request }) {
   const url = new URL(request.url);
@@ -34,3 +34,24 @@ async function importServerReference(id: string) {
     return importReference();
   }
 }
+
+async function decodeActionRequest(
+  request: Request,
+): Promise<ServerActionPayload> {
+  const contentType = request.headers.get("content-type");
+  tinyassert(contentType);
+  if (contentType === "application/json") {
+    return request.json();
+  } else {
+    const formData = await request.formData();
+    const id = formData.get("__id");
+    const name = formData.get("__name");
+    tinyassert(typeof id === "string");
+    tinyassert(typeof name === "string");
+    return {
+      id,
+      name,
+      args: [formData],
+    };
+  }
+}
diff --git a/examples/vue-ssr-extra/src/features/server-action/shared.ts b/examples/vue-ssr-extra/src/features/server-action/shared.ts
index 1eadc74e..90a3870c 100644
--- a/examples/vue-ssr-extra/src/features/server-action/shared.ts
+++ b/examples/vue-ssr-extra/src/features/server-action/shared.ts
@@ -1,11 +1,11 @@
 import { tinyassert } from "@hiogawa/utils";
-import { defineComponent, h, ref } from "vue";
+import { defineComponent, h, ref, type PropType } from "vue";
 
 export const ACTION_PATH = "/__action";
 
 type FormAction<T = any> = (v: FormData) => Promise<T>;
 
-type ServerActionPayload = {
+export type ServerActionPayload = {
   id: string;
   name: string;
   args: unknown[];
@@ -27,7 +27,7 @@ export function registerServerReference<T extends object>(
 export const Form = defineComponent({
   props: {
     action: {
-      type: Function,
+      type: Function as PropType<FormAction>,
       required: true,
     },
   },
@@ -84,6 +84,7 @@ export function useEnhance<T>(
   const status = ref<"idle" | "pending" | "success">("idle");
   const enhanced: FormAction<void> = async (v) => {
     status.value = "pending";
+    // TODO: what if unmounted before finishing action?
     const result = await action(v);
     options?.onSuccess(result);
     status.value = "success";
@@ -91,43 +92,3 @@ export function useEnhance<T>(
   const newAction = registerServerReference(enhanced, meta.__id, meta.__name);
   return [newAction, { status }] as const;
 }
-
-export function encodeActionRequest(
-  id: string,
-  name: string,
-  args: unknown[],
-): RequestInit {
-  if (args.length === 1 && args[0] instanceof FormData) {
-    return {
-      body: args[0],
-    };
-  } else {
-    return {
-      body: JSON.stringify({ id, name, args } satisfies ServerActionPayload),
-      headers: {
-        "content-type": "application/json",
-      },
-    };
-  }
-}
-
-export async function decodeActionRequest(
-  request: Request,
-): Promise<ServerActionPayload> {
-  const contentType = request.headers.get("content-type");
-  tinyassert(contentType);
-  if (contentType === "application/json") {
-    return request.json();
-  } else {
-    const formData = await request.formData();
-    const id = formData.get("__id");
-    const name = formData.get("__name");
-    tinyassert(typeof id === "string");
-    tinyassert(typeof name === "string");
-    return {
-      id,
-      name,
-      args: [formData],
-    };
-  }
-}