refactor: remove unused tool filter middleware and helpers

- Deleted tool_filter_middleware_test.go and tool_helpers.go as they are no longer needed.
- Removed associated test cases in tool_helpers_test.go.
- Refactored knowledge retriever logic by moving it to a new file and updating imports.
- Introduced tooling package for tool result reduction logic.
- Updated traces package to include new trace types and structures.
- Adjusted executor and tool search tool to reflect new package structure.

internal/ai/runtime/tooling/tool_result_reducer.go

@@ -0,0 +1,102 @@
+package tooling
+
+import (
+	"encoding/json"
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+
+	"agent-desk/internal/ai/mcps"
+)
+
+const (
+	maxToolResultSummaryChars = 4000
+	maxToolResultSegments     = 12
+)
+
+var reductionInfoPattern = regexp.MustCompile(`\[tool result reduced: original_length=(\d+), kept_length=(\d+)\]`)
+
+type ReductionInfo struct {
+	Reduced       bool
+	OriginalChars int
+	KeptChars     int
+}
+
+// BuildReducedToolResultSummary returns a bounded text summary for MCP tool results.
+// It keeps the main payload visible to the model while preventing a single large tool
+// response from exhausting too much context.
+func BuildReducedToolResultSummary(result *mcps.ToolCallResult) string {
+	if result == nil {
+		return ""
+	}
+	segments := collectToolResultSegments(result)
+	if len(segments) == 0 {
+		return ""
+	}
+	text := strings.TrimSpace(strings.Join(segments, "\n"))
+	if text == "" {
+		return ""
+	}
+	runes := []rune(text)
+	if len(runes) <= maxToolResultSummaryChars {
+		return text
+	}
+	truncated := strings.TrimSpace(string(runes[:maxToolResultSummaryChars]))
+	return fmt.Sprintf("%s\n\n[tool result reduced: original_length=%d, kept_length=%d]", truncated, len(runes), maxToolResultSummaryChars)
+}
+
+func ParseReductionInfo(summary string) ReductionInfo {
+	matches := reductionInfoPattern.FindStringSubmatch(strings.TrimSpace(summary))
+	if len(matches) != 3 {
+		return ReductionInfo{}
+	}
+	originalChars, err1 := strconv.Atoi(matches[1])
+	keptChars, err2 := strconv.Atoi(matches[2])
+	if err1 != nil || err2 != nil {
+		return ReductionInfo{}
+	}
+	return ReductionInfo{
+		Reduced:       true,
+		OriginalChars: originalChars,
+		KeptChars:     keptChars,
+	}
+}
+
+func collectToolResultSegments(result *mcps.ToolCallResult) []string {
+	segments := make([]string, 0, len(result.Content)+2)
+	if result.IsError {
+		segments = append(segments, "tool returned an error")
+	}
+	if result.StructuredContent != nil {
+		if data, err := json.Marshal(result.StructuredContent); err == nil {
+			segments = appendNonBlankSegment(segments, string(data))
+		}
+	}
+	for _, item := range result.Content {
+		if len(segments) >= maxToolResultSegments {
+			segments = append(segments, "[tool result reduced: remaining segments omitted]")
+			break
+		}
+		switch item.Type {
+		case "text":
+			segments = appendNonBlankSegment(segments, item.Text)
+		default:
+			if item.Data == nil {
+				continue
+			}
+			if data, err := json.Marshal(item.Data); err == nil {
+				segments = appendNonBlankSegment(segments, string(data))
+			}
+		}
+	}
+	return segments
+}
+
+func appendNonBlankSegment(input []string, value string) []string {
+	value = strings.TrimSpace(value)
+	if value == "" {
+		return input
+	}
+	return append(input, value)
+}