Remove duplicate ChatService flow tests and harden null-input test

- Remove 4 ChatServiceTests that duplicated existing tests covering
  identical code paths (structured-syntax success, classifier miss,
  explicit RequestProposal failure, actionable-but-parser-fails)
- Change Classify_NullInput test to assert base Exception instead of
  NullReferenceException so it survives addition of a null guard

Author: Chris0Jeky

backend/tests/Taskdeck.Application.Tests/Services/ChatServiceTests.cs

@@ -760,180 +760,6 @@ public async Task GetProviderHealthAsync_ShouldUseProbeStatus_WhenRequested()
         _llmProviderMock.Verify(p => p.GetHealthAsync(default), Times.Never);
     }
 
-    #region Chat-to-Proposal Flow — Classifier → Parser Integration (#577)
-
-    /// <summary>
-    /// Full flow: structured syntax hits the LLM classifier (IsActionable=true),
-    /// then the planner parses successfully, yielding a proposal reference.
-    /// </summary>
-    [Fact]
-    public async Task SendMessageAsync_StructuredSyntax_ClassifierHit_ParserSuccess_ProposalCreated()
-    {
-        var userId = Guid.NewGuid();
-        var boardId = Guid.NewGuid();
-        var proposalId = Guid.NewGuid();
-        var session = new ChatSession(userId, "Full flow session", boardId);
-
-        _chatSessionRepoMock
-            .Setup(r => r.GetByIdWithMessagesAsync(session.Id, default))
-            .ReturnsAsync(session);
-        _llmProviderMock
-            .Setup(p => p.CompleteAsync(It.IsAny<ChatCompletionRequest>(), default))
-            .ReturnsAsync(new LlmCompletionResult(
-                "I'll create that card.", 15, true, "card.create"));
-        _plannerMock
-            .Setup(p => p.ParseInstructionAsync(
-                It.IsAny<string>(), userId, boardId,
-                It.IsAny<CancellationToken>(), ProposalSourceType.Chat,
-                session.Id.ToString(), It.IsAny<string?>()))
-            .ReturnsAsync(Result.Success(new ProposalDto(
-                proposalId, ProposalSourceType.Chat, null, boardId, userId,
-                ProposalStatus.PendingReview, RiskLevel.Low,
-                "create card 'Deploy script'", null, null,
-                DateTimeOffset.UtcNow, DateTimeOffset.UtcNow,
-                DateTime.UtcNow.AddHours(1), null, null, null, null,
-                "corr", new List<ProposalOperationDto>())));
-
-        var result = await _service.SendMessageAsync(
-            session.Id,
-            userId,
-            new SendChatMessageDto("create card 'Deploy script'"),
-            default);
-
-        result.IsSuccess.Should().BeTrue();
-        result.Value.MessageType.Should().Be("proposal-reference");
-        result.Value.ProposalId.Should().Be(proposalId);
-        result.Value.Content.Should().Contain("Proposal created for review");
-        _plannerMock.Verify(
-            p => p.ParseInstructionAsync(
-                "create card 'Deploy script'", userId, boardId,
-                It.IsAny<CancellationToken>(), ProposalSourceType.Chat,
-                session.Id.ToString(), It.IsAny<string?>()),
-            Times.Once);
-    }
-
-    /// <summary>
-    /// Natural language misses classifier (IsActionable=false), no RequestProposal set,
-    /// so the planner is never called — current behavior documents the gap.
-    /// </summary>
-    [Fact]
-    public async Task SendMessageAsync_NaturalLanguage_ClassifierMiss_NoPlannerCall()
-    {
-        var userId = Guid.NewGuid();
-        var boardId = Guid.NewGuid();
-        var session = new ChatSession(userId, "Classifier miss session", boardId);
-
-        _chatSessionRepoMock
-            .Setup(r => r.GetByIdWithMessagesAsync(session.Id, default))
-            .ReturnsAsync(session);
-        _llmProviderMock
-            .Setup(p => p.CompleteAsync(It.IsAny<ChatCompletionRequest>(), default))
-            .ReturnsAsync(new LlmCompletionResult(
-                "Sure, I can help with that.", 10, false, null));
-
-        var result = await _service.SendMessageAsync(
-            session.Id,
-            userId,
-            new SendChatMessageDto("set up some tasks for the sprint"),
-            default);
-
-        result.IsSuccess.Should().BeTrue();
-        result.Value.MessageType.Should().Be("text");
-        _plannerMock.Verify(
-            p => p.ParseInstructionAsync(
-                It.IsAny<string>(), It.IsAny<Guid>(), It.IsAny<Guid?>(),
-                It.IsAny<CancellationToken>(), It.IsAny<ProposalSourceType>(),
-                It.IsAny<string?>(), It.IsAny<string?>()),
-            Times.Never,
-            "planner should not be called when classifier reports non-actionable and RequestProposal is false");
-    }
-
-    /// <summary>
-    /// Explicit RequestProposal with natural language — parser receives the raw
-    /// message and fails because it only understands structured syntax.
-    /// </summary>
-    [Fact]
-    public async Task SendMessageAsync_ExplicitRequestProposal_NaturalLanguage_ParserFailsGracefully()
-    {
-        var userId = Guid.NewGuid();
-        var boardId = Guid.NewGuid();
-        var session = new ChatSession(userId, "Explicit NLP fail session", boardId);
-
-        _chatSessionRepoMock
-            .Setup(r => r.GetByIdWithMessagesAsync(session.Id, default))
-            .ReturnsAsync(session);
-        _llmProviderMock
-            .Setup(p => p.CompleteAsync(It.IsAny<ChatCompletionRequest>(), default))
-            .ReturnsAsync(new LlmCompletionResult(
-                "I understand you want tasks.", 15, false, null));
-        _plannerMock
-            .Setup(p => p.ParseInstructionAsync(
-                It.IsAny<string>(), userId, boardId,
-                It.IsAny<CancellationToken>(), It.IsAny<ProposalSourceType>(),
-                It.IsAny<string?>(), It.IsAny<string?>()))
-            .ReturnsAsync(Result.Failure<ProposalDto>(
-                ErrorCodes.ValidationError,
-                "Could not parse instruction. Supported patterns: 'create card \"title\"'..."));
-
-        var result = await _service.SendMessageAsync(
-            session.Id,
-            userId,
-            new SendChatMessageDto(
-                "please create some tasks for the deployment checklist",
-                RequestProposal: true),
-            default);
-
-        result.IsSuccess.Should().BeTrue();
-        result.Value.MessageType.Should().Be("status");
-        result.Value.Content.Should().Contain("Could not create the requested proposal");
-        _plannerMock.Verify(
-            p => p.ParseInstructionAsync(
-                It.IsAny<string>(), userId, boardId,
-                It.IsAny<CancellationToken>(), ProposalSourceType.Chat,
-                session.Id.ToString(), It.IsAny<string?>()),
-            Times.Once);
-    }
-
-    /// <summary>
-    /// Classifier detects actionable intent but parser fails on the raw message
-    /// (e.g., message says "create card for testing" but lacks quoted title).
-    /// Verifies the hint message is shown to the user.
-    /// </summary>
-    [Fact]
-    public async Task SendMessageAsync_ActionableClassification_ParserFails_ShowsParseHint()
-    {
-        var userId = Guid.NewGuid();
-        var boardId = Guid.NewGuid();
-        var session = new ChatSession(userId, "Actionable parse fail", boardId);
-
-        _chatSessionRepoMock
-            .Setup(r => r.GetByIdWithMessagesAsync(session.Id, default))
-            .ReturnsAsync(session);
-        _llmProviderMock
-            .Setup(p => p.CompleteAsync(It.IsAny<ChatCompletionRequest>(), default))
-            .ReturnsAsync(new LlmCompletionResult(
-                "I'll help you create that.", 10, true, "card.create"));
-        _plannerMock
-            .Setup(p => p.ParseInstructionAsync(
-                It.IsAny<string>(), userId, boardId,
-                It.IsAny<CancellationToken>(), It.IsAny<ProposalSourceType>(),
-                It.IsAny<string?>(), It.IsAny<string?>()))
-            .ReturnsAsync(Result.Failure<ProposalDto>(
-                ErrorCodes.ValidationError, "Could not parse instruction"));
-
-        var result = await _service.SendMessageAsync(
-            session.Id,
-            userId,
-            new SendChatMessageDto("create card for testing without quotes"),
-            default);
-
-        result.IsSuccess.Should().BeTrue();
-        result.Value.MessageType.Should().Be("status");
-        result.Value.Content.Should().Contain("detected a task request but could not parse it");
-    }
-
-    #endregion
-
     #region NLP Gap Tests — Documents #570 (Chat-to-Proposal NLP Gap)
 
     /// <summary>

backend/tests/Taskdeck.Application.Tests/Services/LlmIntentClassifierTests.cs

@@ -145,13 +145,15 @@ public void Classify_NonActionable_ShouldReturnFalse(string message)
     #region Edge Cases — Input Extremes
 
     [Fact]
-    public void Classify_NullInput_ThrowsNullReferenceException()
+    public void Classify_NullInput_Throws()
     {
         // The classifier calls message.ToLowerInvariant() without a null guard.
         // This documents that null input is not handled gracefully.
+        // Using base Exception type so the test survives if a null guard
+        // (ArgumentNullException) is added later.
         var act = () => LlmIntentClassifier.Classify(null!);
 
-        act.Should().Throw<NullReferenceException>();
+        act.Should().Throw<Exception>();
     }
 
     [Fact]