Add rolemaster situational roll modifier backend

RpgRoller.Tests/Api/RolemasterApiTests.cs

@@ -141,4 +141,45 @@ public sealed class RolemasterApiTests(WebApplicationFactory<Program> factory) :
             Assert.Equal(RollDieKinds.RolemasterOpenEndedInitial, die.Kind);
         });
     }
+
+    [Fact]
+    public async Task RolemasterSkillRoll_AcceptsSituationalModifier_AndAppliesItToRetryMath()
+    {
+        using var factory = CreateFactory(8, 42);
+        using var client = factory.CreateClient(new() { AllowAutoRedirect = false });
+
+        await RegisterAsync(client, "rolemaster-situational-api", "Password123", "Rolemaster Situational Api");
+        await LoginAsync(client, "rolemaster-situational-api", "Password123");
+
+        var campaign = await PostAsync<CreateCampaignRequest, CampaignSummary>(client, "/api/campaigns", new("Rolemaster Situational", "rolemaster"));
+        var character = await PostAsync<CreateCharacterRequest, CharacterSummary>(client, "/api/characters", new("Hero", campaign.Id));
+        var skill = await PostAsync<CreateSkillRequest, SkillSummary>(client, $"/api/characters/{character.Id}/skills", new("Observation", "d100!+50", 0, false, null, 5, true));
+
+        var roll = await PostAsync<RollSkillRequest, RollResult>(client, $"/api/skills/{skill.Id}/roll", new("public", 20));
+
+        Assert.Equal(117, roll.Result);
+        Assert.Equal("8+50+20=78; retry(+5): 42+50+20=112; final=117", roll.Breakdown);
+        Assert.Collection(roll.Dice, die => Assert.Equal(1, die.Attempt), die => Assert.Equal(2, die.Attempt));
+    }
+
+    [Fact]
+    public async Task SkillRoll_RejectsSituationalModifier_ForNonRolemasterCampaigns()
+    {
+        using var factory = CreateFactory(12);
+        using var client = factory.CreateClient(new() { AllowAutoRedirect = false });
+
+        await RegisterAsync(client, "non-rolemaster-situational-api", "Password123", "Non Rolemaster Situational Api");
+        await LoginAsync(client, "non-rolemaster-situational-api", "Password123");
+
+        var campaign = await PostAsync<CreateCampaignRequest, CampaignSummary>(client, "/api/campaigns", new("Dnd Situational", "dnd5e"));
+        var character = await PostAsync<CreateCharacterRequest, CharacterSummary>(client, "/api/characters", new("Hero", campaign.Id));
+        var skill = await PostAsync<CreateSkillRequest, SkillSummary>(client, $"/api/characters/{character.Id}/skills", new("Attack", "1d20+5", 0, false));
+
+        var response = await client.PostAsJsonAsync($"/api/skills/{skill.Id}/roll", new RollSkillRequest("public", 20));
+        var error = await response.Content.ReadFromJsonAsync<ApiError>();
+
+        Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
+        Assert.NotNull(error);
+        Assert.Equal("invalid_situational_modifier", error.Code);
+    }
 }