feat(observability): add MCP tool name logging in access log

* Include tool name from request in access log entries
* Update user agent header in HTTP requests
* Add tests for MCP tool name logging

internal/observability/http.go

@@ -1,10 +1,14 @@
 package observability
 
 import (
+	"bytes"
 	"context"
+	"encoding/json"
+	"io"
 	"log/slog"
 	"net/http"
 	"runtime/debug"
+	"strings"
 	"time"
 
 	"github.com/google/uuid"
@@ -15,6 +19,7 @@ import (
 type contextKey string
 
 const requestIDContextKey contextKey = "request_id"
+const mcpToolContextKey contextKey = "mcp_tool"
 
 func Chain(h http.Handler, middlewares ...func(http.Handler) http.Handler) http.Handler {
 	for i := len(middlewares) - 1; i >= 0; i-- {
@@ -58,18 +63,26 @@ func Recover(log *slog.Logger) func(http.Handler) http.Handler {
 func AccessLog(log *slog.Logger) func(http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if tool := mcpToolFromRequest(r); tool != "" {
+				r = r.WithContext(context.WithValue(r.Context(), mcpToolContextKey, tool))
+			}
+
 			recorder := &statusRecorder{ResponseWriter: w, status: http.StatusOK}
 			started := time.Now()
 			next.ServeHTTP(recorder, r)
 
-			log.Info("http request",
+			attrs := []any{
 				slog.String("request_id", RequestIDFromContext(r.Context())),
 				slog.String("method", r.Method),
 				slog.String("path", r.URL.Path),
 				slog.Int("status", recorder.status),
 				slog.Duration("duration", time.Since(started)),
 				slog.String("remote_addr", requestip.FromRequest(r)),
-			)
+			}
+			if tool, _ := r.Context().Value(mcpToolContextKey).(string); strings.TrimSpace(tool) != "" {
+				attrs = append(attrs, slog.String("tool", tool))
+			}
+			log.Info("http request", attrs...)
 		})
 	}
 }
@@ -101,3 +114,52 @@ func (s *statusRecorder) WriteHeader(statusCode int) {
 	s.status = statusCode
 	s.ResponseWriter.WriteHeader(statusCode)
 }
+
+func mcpToolFromRequest(r *http.Request) string {
+	if r == nil || r.Method != http.MethodPost || !strings.HasPrefix(r.URL.Path, "/mcp") || r.Body == nil {
+		return ""
+	}
+
+	raw, err := io.ReadAll(r.Body)
+	if err != nil {
+		return ""
+	}
+	r.Body = io.NopCloser(bytes.NewReader(raw))
+	if len(raw) == 0 {
+		return ""
+	}
+
+	// Support both single and batch JSON-RPC payloads.
+	if strings.HasPrefix(strings.TrimSpace(string(raw)), "[") {
+		var batch []rpcEnvelope
+		if err := json.Unmarshal(raw, &batch); err != nil {
+			return ""
+		}
+		for _, msg := range batch {
+			if tool := msg.toolName(); tool != "" {
+				return tool
+			}
+		}
+		return ""
+	}
+
+	var msg rpcEnvelope
+	if err := json.Unmarshal(raw, &msg); err != nil {
+		return ""
+	}
+	return msg.toolName()
+}
+
+type rpcEnvelope struct {
+	Method string `json:"method"`
+	Params struct {
+		Name string `json:"name"`
+	} `json:"params"`
+}
+
+func (m rpcEnvelope) toolName() string {
+	if m.Method != "tools/call" {
+		return ""
+	}
+	return strings.TrimSpace(m.Params.Name)
+}