압축 경계에서도 tool pair 불변식을 유지하도록 보강

claw-code의 sessionMemoryCompact 흐름을 참고해 AX Agent가 recent window를 자를 때도 tool_use/tool_result 짝이 끊기지 않도록 보정 범위를 넓혔다.

- AgentMessageInvariantHelper를 추가해 tool_result와 assistant _tool_use_blocks 대응 관계를 공용 로직으로 정리

- AgentQueryContextBuilder는 공용 helper를 사용하도록 단순화

- ContextCondenser의 microcompact, session memory compact, snip, 요약 단계가 모두 같은 split helper로 recent window를 계산하도록 조정

- compaction split 시 recent window 안의 tool_result가 old window의 tool_use를 잃는 상황을 줄여 API pairing 안정성을 높임

- README.md, docs/DEVELOPMENT.md에 2026-04-12 21:39 (KST) 기준 이력 반영

검증: dotnet build src/AxCopilot/AxCopilot.csproj -c Release -v minimal -p:OutputPath=bin\\verify\\ -p:IntermediateOutputPath=obj\\verify\\ / 경고 0, 오류 0

src/AxCopilot/Services/Agent/AgentQueryContextBuilder.cs

@@ -47,7 +47,7 @@ public static class AgentQueryContextBuilder
         }
 
         var startIndex = FindWindowStartIndex(sourceMessages, out var boundaryApplied);
-        var adjustedStartIndex = AdjustStartIndexForToolPairs(sourceMessages, startIndex, out var preservedToolPairs);
+        var adjustedStartIndex = AgentMessageInvariantHelper.AdjustStartIndexForToolPairs(sourceMessages, startIndex, out var preservedToolPairs);
         var toolPairExpanded = adjustedStartIndex < startIndex;
 
         var windowMessages = new List<ChatMessage>(sourceMessages.Count);
@@ -112,120 +112,6 @@ public static class AgentQueryContextBuilder
                || content.StartsWith("[이전 압축 경계 병합", StringComparison.Ordinal);
     }
 
-    private static int AdjustStartIndexForToolPairs(
-        IReadOnlyList<ChatMessage> sourceMessages,
-        int startIndex,
-        out int preservedToolPairs)
-    {
-        preservedToolPairs = 0;
-        if (startIndex <= 0)
-            return startIndex;
-
-        var toolResultIds = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
-        for (var i = startIndex; i < sourceMessages.Count; i++)
-        {
-            if (!TryGetToolResultId(sourceMessages[i], out var toolResultId))
-                continue;
-
-            toolResultIds.Add(toolResultId);
-        }
-
-        if (toolResultIds.Count == 0)
-            return startIndex;
-
-        var toolUseIdsInWindow = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
-        for (var i = startIndex; i < sourceMessages.Count; i++)
-        {
-            foreach (var toolUseId in EnumerateToolUseIds(sourceMessages[i]))
-                toolUseIdsInWindow.Add(toolUseId);
-        }
-
-        toolResultIds.ExceptWith(toolUseIdsInWindow);
-        if (toolResultIds.Count == 0)
-            return startIndex;
-
-        var adjustedStart = startIndex;
-        for (var i = startIndex - 1; i >= 0 && toolResultIds.Count > 0; i--)
-        {
-            var foundAny = false;
-            foreach (var toolUseId in EnumerateToolUseIds(sourceMessages[i]))
-            {
-                if (!toolResultIds.Remove(toolUseId))
-                    continue;
-
-                preservedToolPairs++;
-                foundAny = true;
-            }
-
-            if (foundAny)
-                adjustedStart = i;
-        }
-
-        return adjustedStart;
-    }
-
-    private static bool TryGetToolResultId(ChatMessage message, out string toolResultId)
-    {
-        toolResultId = "";
-        if (!string.Equals(message.Role, "user", StringComparison.OrdinalIgnoreCase))
-            return false;
-
-        var content = message.Content ?? "";
-        if (!content.StartsWith("{\"type\":\"tool_result\"", StringComparison.Ordinal))
-            return false;
-
-        try
-        {
-            using var doc = JsonDocument.Parse(content);
-            toolResultId = doc.RootElement.TryGetProperty("tool_use_id", out var idEl)
-                ? idEl.GetString() ?? ""
-                : "";
-            return !string.IsNullOrWhiteSpace(toolResultId);
-        }
-        catch
-        {
-            return false;
-        }
-    }
-
-    private static IEnumerable<string> EnumerateToolUseIds(ChatMessage message)
-    {
-        if (!string.Equals(message.Role, "assistant", StringComparison.OrdinalIgnoreCase))
-            yield break;
-
-        var content = message.Content ?? "";
-        if (!content.StartsWith("{\"_tool_use_blocks\"", StringComparison.Ordinal))
-            yield break;
-
-        JsonDocument? doc = null;
-        try
-        {
-            doc = JsonDocument.Parse(content);
-            if (!doc.RootElement.TryGetProperty("_tool_use_blocks", out var blocksEl) || blocksEl.ValueKind != JsonValueKind.Array)
-                yield break;
-
-            foreach (var block in blocksEl.EnumerateArray())
-            {
-                if (!block.TryGetProperty("type", out var typeEl)
-                    || !string.Equals(typeEl.GetString(), "tool_use", StringComparison.OrdinalIgnoreCase))
-                {
-                    continue;
-                }
-
-                if (block.TryGetProperty("id", out var idEl))
-                {
-                    var toolUseId = idEl.GetString();
-                    if (!string.IsNullOrWhiteSpace(toolUseId))
-                        yield return toolUseId!;
-                }
-            }
-        }
-        finally
-        {
-            doc?.Dispose();
-        }
-    }
-
     private static int ApplyOldToolResultBudget(List<ChatMessage> messages)
     {
         var nonSystemIndexes = messages
@@ -244,7 +130,7 @@ public static class AgentQueryContextBuilder
         for (var i = 0; i < protectedStart; i++)
         {
             var message = messages[i];
-            if (!TryGetToolResultId(message, out _))
+            if (!AgentMessageInvariantHelper.TryGetToolResultId(message, out _))
                 continue;
 
             var content = message.Content ?? "";