preview 상태 고정과 no-LSP 언어 fallback 마감

목적:
- 긴 세션, compact, query view 생성 시점에도 tool_result preview 축약 상태를 더 안정적으로 유지합니다.
- 격리 환경에서 로컬 LSP 서버가 없더라도 코드 탭이 언어별 정적 분석 힌트를 계속 제공하도록 마감합니다.
- 설정/프롬프트/로드맵 문서까지 현재 구현 상태와 일치시키고 남은 고도화 범위를 정리합니다.

핵심 수정:
- AgentQueryContextBuilder와 ContextCondenser가 query/compact 진입 전에 누락된 tool_result preview를 먼저 복원하도록 정리했습니다.
- AgentToolResultBudget는 sourceMessages가 없는 호출에서도 현재 window의 tool_use_id preview를 재사용하도록 보강했습니다.
- CodeLanguageCatalog에 언어별 manifest/build/test/lint fallback 힌트를 추가하고, LspTool은 LSP 서버 미가동 시 정적 fallback 안내를 반환하도록 변경했습니다.
- SettingsViewModel, SettingsWindow, ChatWindow.SystemPromptBuilder에 Fallback 분석 설명과 LSP 미사용 시 대체 분석 지침을 반영했습니다.
- AgentQueryContextBuilderTests를 새로 추가하고 AgentToolResultBudgetTests, CodeLanguageCatalogTests를 확장했습니다.
- README.md, docs/DEVELOPMENT.md, docs/AGENT_ROADMAP.md, docs/NEXT_ROADMAP.md를 2026-04-15 08:32 (KST) 기준으로 갱신했습니다.

검증:
- dotnet build src/AxCopilot/AxCopilot.csproj -c Release -v minimal -p:OutputPath=bin\\verify_loop_lang_finish\\ -p:IntermediateOutputPath=obj\\verify_loop_lang_finish\\
- dotnet test src/AxCopilot.Tests/AxCopilot.Tests.csproj -c Release -v minimal --filter "AgentToolResultBudgetTests|AgentQueryContextBuilderTests|CodeLanguageCatalogTests|ContextCondenserTests" -p:OutputPath=bin\\verify_loop_lang_finish_tests\\ -p:IntermediateOutputPath=obj\\verify_loop_lang_finish_tests\\ (통과 20)

src/AxCopilot.Tests/Services/AgentQueryContextBuilderTests.cs

@@ -0,0 +1,42 @@
+using AxCopilot.Models;
+using AxCopilot.Services.Agent;
+using FluentAssertions;
+using Xunit;
+
+namespace AxCopilot.Tests.Services;
+
+public class AgentQueryContextBuilderTests
+{
+    [Fact]
+    public void Build_ShouldPopulateMissingToolResultPreviewBeforeCreatingQueryView()
+    {
+        var longContent = new string('Z', 1800);
+        var sourceMessages = new List<ChatMessage>
+        {
+            new()
+            {
+                MsgId = "tool-source-1",
+                Role = "user",
+                Content = $$"""{"type":"tool_result","tool_use_id":"call-view","tool_name":"file_read","content":"{{longContent}}"}""",
+                QueryPreviewContent = """{"type":"tool_result","tool_use_id":"call-view","tool_name":"file_read","content":"preview-view"}"""
+            },
+            new()
+            {
+                MsgId = "tool-source-2",
+                Role = "user",
+                Content = $$"""{"type":"tool_result","tool_use_id":"call-view","tool_name":"file_read","content":"{{longContent}}"}"""
+            },
+            new()
+            {
+                MsgId = "tail-1",
+                Role = "assistant",
+                Content = "recent tail"
+            }
+        };
+
+        var result = AgentQueryContextBuilder.Build(sourceMessages);
+
+        sourceMessages[1].QueryPreviewContent.Should().Be(sourceMessages[0].QueryPreviewContent);
+        result.Messages[1].QueryPreviewContent.Should().Be(sourceMessages[0].QueryPreviewContent);
+    }
+}

src/AxCopilot.Tests/Services/AgentToolResultBudgetTests.cs

@@ -98,4 +98,37 @@ public class AgentToolResultBudgetTests
         result.ReusedPreviewCount.Should().Be(1);
         queryView[0].Content.Should().Be(sourceMessages[0].QueryPreviewContent);
     }
+
+    [Fact]
+    public void Apply_ShouldReusePreviewWithinSameWindow_WhenSourceMessagesAreOmitted()
+    {
+        var longContent = new string('C', 1600);
+        var queryView = new List<ChatMessage>
+        {
+            new()
+            {
+                MsgId = "tool-1",
+                Role = "user",
+                Content = $$"""{"type":"tool_result","tool_use_id":"call-inline","tool_name":"file_read","content":"{{longContent}}"}""",
+                QueryPreviewContent = """{"type":"tool_result","tool_use_id":"call-inline","tool_name":"file_read","content":"preview-inline"}"""
+            },
+            new()
+            {
+                MsgId = "tool-2",
+                Role = "user",
+                Content = $$"""{"type":"tool_result","tool_use_id":"call-inline","tool_name":"file_read","content":"{{longContent}}"}"""
+            },
+            new()
+            {
+                MsgId = "tail-1",
+                Role = "assistant",
+                Content = "recent tail"
+            }
+        };
+
+        var result = AgentToolResultBudget.Apply(queryView, protectedRecentNonSystemMessages: 1);
+
+        result.ReusedPreviewCount.Should().BeGreaterThan(0);
+        queryView[1].QueryPreviewContent.Should().Be(queryView[0].QueryPreviewContent);
+    }
 }

src/AxCopilot.Tests/Services/CodeLanguageCatalogTests.cs

@@ -46,4 +46,15 @@ public class CodeLanguageCatalogTests
         CodeLanguageCatalog.BuildQuickSelectSupportDescription().Should().Contain("JavaScript / Vue");
         CodeLanguageCatalog.BuildQuickSelectSupportDescription().Should().NotContain("Go");
     }
+
+    [Fact]
+    public void BuildFallbackSummary_ShouldExposeManifestAndBuildHints()
+    {
+        var summary = CodeLanguageCatalog.BuildFallbackSummary("sample.go");
+
+        summary.Should().Contain("정적 fallback 분석: Go");
+        summary.Should().Contain("go.mod");
+        summary.Should().Contain("go build ./...");
+        summary.Should().Contain("go test ./...");
+    }
 }