test: cover empty pairing request body

apps/windows_agent/tests/TermRemoteCtl.Agent.IntegrationTests/Api/PairingEndpointsTests.cs

@@ -52,6 +52,23 @@ public sealed class PairingEndpointsTests
         Assert.Equal("rejected", payload.Status);
     }
 
+    [Fact]
+    public async Task Redeem_Returns_BadRequest_When_Request_Body_Is_Empty()
+    {
+        await using var fixture = new PairingApiFixture();
+        using var client = fixture.CreateClient();
+        using var content = new StringContent(string.Empty, Encoding.UTF8, "application/json");
+
+        using var response = await client.PostAsync("/api/pairing/redeem", content);
+        var payload = await response.Content.ReadFromJsonAsync<RedeemResponse>();
+
+        Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
+        Assert.NotNull(payload);
+        Assert.False(payload.Success);
+        Assert.Equal("invalid_request", payload.ErrorCode);
+        Assert.Equal("rejected", payload.Status);
+    }
+
     [Fact]
     public async Task CreateCode_Does_Not_Write_Secret_Code_To_Audit_Log()
     {