feat(trace): 深追踪（Span 生命周期/父子链/JSONL recorder，支持 llm/tool/state 等类别）

internal/runtime/trace/json_recorder.go

@@ -0,0 +1,41 @@
+package trace
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"sync"
+)
+
+// Writer persists a completed span. Implementations must be safe for concurrent
+// use, as WriteSpan may be called from several goroutines. A Writer such as
+// *JSONRecorder provides structured local logging for the M9 panel.
+type Writer interface {
+	// WriteSpan persists a single completed span and returns any encoding or
+	// write error.
+	WriteSpan(rec SpanRecord) error
+}
+
+// JSONRecorder writes each completed span as one line of JSON (JSONL) to an
+// underlying io.Writer. It is safe for concurrent use.
+type JSONRecorder struct {
+	mu  sync.Mutex
+	enc *json.Encoder
+}
+
+// NewJSONRecorder builds a JSONRecorder that appends one JSON object per span to
+// out.
+func NewJSONRecorder(out io.Writer) *JSONRecorder {
+	return &JSONRecorder{enc: json.NewEncoder(out)}
+}
+
+// WriteSpan encodes rec as JSON followed by a newline. Concurrent calls are
+// serialized so a single span object is never interleaved with another.
+func (r *JSONRecorder) WriteSpan(rec SpanRecord) error {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	if err := r.enc.Encode(rec); err != nil {
+		return fmt.Errorf("trace: encode span %q: %w", rec.ID, err)
+	}
+	return nil
+}