From c5c872a3731397f6921ff5b87f704fc76a0274cf Mon Sep 17 00:00:00 2001
From: Manuel Ganter <manuel.ganter@think-ahead.tech>
Date: Fri, 6 Feb 2026 11:00:34 +0100
Subject: [PATCH] fix(output): correct JSON serialization of top process
 metrics

slog.Any() does not properly serialize slices of slog.Group() attributes,
resulting in broken output like {"Key":"","Value":{}}. Fixed by passing
structs with JSON tags directly to slog.Any() instead.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
---
 internal/output/logger.go  | 46 +++++++++++++++++++++++++-------------
 internal/summary/writer.go | 24 ++------------------
 2 files changed, 32 insertions(+), 38 deletions(-)

diff --git a/internal/output/logger.go b/internal/output/logger.go
index 0ce5ddd..4c57794 100644
--- a/internal/output/logger.go
+++ b/internal/output/logger.go
@@ -53,26 +53,40 @@ func NewLoggerWriter(cfg LoggerConfig) *LoggerWriter {
 	}
 }
 
+// topCPUEntry is a lightweight struct for JSON serialization of top CPU processes
+type topCPUEntry struct {
+	PID        int     `json:"pid"`
+	Name       string  `json:"name"`
+	CPUPercent float64 `json:"cpu_percent"`
+}
+
+// topMemEntry is a lightweight struct for JSON serialization of top memory processes
+type topMemEntry struct {
+	PID      int    `json:"pid"`
+	Name     string `json:"name"`
+	RSSBytes uint64 `json:"rss_bytes"`
+}
+
 // Write outputs the metrics using structured logging
 func (w *LoggerWriter) Write(m *metrics.SystemMetrics) error {
-	// Build top CPU process attrs
-	topCPUAttrs := make([]any, 0, len(m.TopCPU))
+	// Build top CPU process entries
+	topCPU := make([]topCPUEntry, 0, len(m.TopCPU))
 	for _, p := range m.TopCPU {
-		topCPUAttrs = append(topCPUAttrs, slog.Group("",
-			slog.Int("pid", p.PID),
-			slog.String("name", p.Name),
-			slog.Float64("cpu_percent", p.CPUPercent),
-		))
+		topCPU = append(topCPU, topCPUEntry{
+			PID:        p.PID,
+			Name:       p.Name,
+			CPUPercent: p.CPUPercent,
+		})
 	}
 
-	// Build top memory process attrs
-	topMemAttrs := make([]any, 0, len(m.TopMemory))
+	// Build top memory process entries
+	topMem := make([]topMemEntry, 0, len(m.TopMemory))
 	for _, p := range m.TopMemory {
-		topMemAttrs = append(topMemAttrs, slog.Group("",
-			slog.Int("pid", p.PID),
-			slog.String("name", p.Name),
-			slog.Uint64("rss_bytes", p.MemRSS),
-		))
+		topMem = append(topMem, topMemEntry{
+			PID:      p.PID,
+			Name:     p.Name,
+			RSSBytes: p.MemRSS,
+		})
 	}
 
 	w.logger.Info("metrics_collected",
@@ -94,8 +108,8 @@ func (w *LoggerWriter) Write(m *metrics.SystemMetrics) error {
 			slog.Uint64("total_rss_bytes", m.Memory.TotalRSSBytes),
 			slog.Float64("rss_percent", m.Memory.RSSPercent),
 		),
-		slog.Any("top_cpu", topCPUAttrs),
-		slog.Any("top_memory", topMemAttrs),
+		slog.Any("top_cpu", topCPU),
+		slog.Any("top_memory", topMem),
 	)
 
 	return nil
diff --git a/internal/summary/writer.go b/internal/summary/writer.go
index f6781e1..30b392b 100644
--- a/internal/summary/writer.go
+++ b/internal/summary/writer.go
@@ -35,26 +35,6 @@ func (w *SummaryWriter) Write(s *RunSummary) {
 		return
 	}
 
-	topCPUAttrs := make([]any, 0, len(s.TopCPUProcesses))
-	for _, p := range s.TopCPUProcesses {
-		topCPUAttrs = append(topCPUAttrs, slog.Group("",
-			slog.Int("pid", p.PID),
-			slog.String("name", p.Name),
-			slog.Float64("peak_cpu_percent", p.PeakCPU),
-			slog.Uint64("peak_mem_rss_bytes", p.PeakMem),
-		))
-	}
-
-	topMemAttrs := make([]any, 0, len(s.TopMemProcesses))
-	for _, p := range s.TopMemProcesses {
-		topMemAttrs = append(topMemAttrs, slog.Group("",
-			slog.Int("pid", p.PID),
-			slog.String("name", p.Name),
-			slog.Float64("peak_cpu_percent", p.PeakCPU),
-			slog.Uint64("peak_mem_rss_bytes", p.PeakMem),
-		))
-	}
-
 	w.logger.Info("run_summary",
 		slog.Time("start_time", s.StartTime),
 		slog.Time("end_time", s.EndTime),
@@ -75,7 +55,7 @@ func (w *SummaryWriter) Write(s *RunSummary) {
 			slog.Float64("avg", s.MemUsedPercent.Avg),
 			slog.Float64("p95", s.MemUsedPercent.P95),
 		),
-		slog.Any("top_cpu_processes", topCPUAttrs),
-		slog.Any("top_mem_processes", topMemAttrs),
+		slog.Any("top_cpu_processes", s.TopCPUProcesses),
+		slog.Any("top_mem_processes", s.TopMemProcesses),
 	)
 }