feat(loop): agent loop（8 轮 + checkpoint + 流式 + 记忆注入/提取 + trace + 工具超时回喂）

internal/runtime/loop/trace.go

@@ -0,0 +1,34 @@
+package loop
+
+import (
+	"context"
+
+	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/trace"
+)
+
+// span starts a named span of the given kind when a Tracer is configured, else
+// returns a nil no-op span. The returned context carries the span as the current
+// one so nested spans chain as children.
+func (l *Loop) span(ctx context.Context, name string, kind trace.SpanKind) (context.Context, *trace.Span) {
+	if l.tracer == nil {
+		return ctx, nil
+	}
+	return l.tracer.StartSpan(ctx, name, kind)
+}
+
+// finishSpan closes a span with the given status, ignoring a nil span.
+func (l *Loop) finishSpan(sp *trace.Span, status trace.SpanStatus) {
+	if sp == nil {
+		return
+	}
+	sp.Finish(status)
+}
+
+// spanProp attaches a structured property to a span, ignoring a nil span and any
+// mutation-after-close error.
+func (l *Loop) spanProp(sp *trace.Span, key string, value any) {
+	if sp == nil {
+		return
+	}
+	_ = sp.SetProp(key, value)
+}