test(media): narrow result kind before sendResult assertion

src/infra/outbound/message-action-runner.test.ts

@@ -624,6 +624,9 @@ describe("runMessageAction sandboxed media validation", () => {
       });
 
       expect(result.kind).toBe("send");
+      if (result.kind !== "send") {
+        throw new Error("expected send result");
+      }
       expect(result.sendResult?.mediaUrl).toBe(tmpFile);
     } finally {
       await fs.rm(sandboxDir, { recursive: true, force: true });