fix(config): real circular include detection with visited set

Replace depth-only detection with path-based visited set tracking.
Detects cycles immediately on first revisit instead of after 10 depth
iterations. Supports diamond patterns (A->B->shared, A->C->shared)
via backtracking. Add self-include and diamond tests. Document that
only servers/stream/variables are merged in defaults.go.

internal/config/config.go

@@ -140,7 +140,9 @@ func Load(path string) (*Config, error) {
 	}
 
 	if len(cfg.Include) > 0 {
-		if err := processIncludes(&cfg, filepath.Dir(path), 0); err != nil {
+		absPath, _ := filepath.Abs(path)
+		visited := map[string]bool{absPath: true}
+		if err := processIncludes(&cfg, filepath.Dir(path), 0, visited); err != nil {
 			return nil, fmt.Errorf("处理配置引入失败: %w", err)
 		}
 	}
@@ -154,9 +156,9 @@ func Load(path string) (*Config, error) {
 
 const maxIncludeDepth = 10
 
-func processIncludes(cfg *Config, baseDir string, depth int) error {
+func processIncludes(cfg *Config, baseDir string, depth int, visited map[string]bool) error {
 	if depth >= maxIncludeDepth {
-		return fmt.Errorf("配置引入嵌套深度超过 %d 层，可能存在循环引入", maxIncludeDepth)
+		return fmt.Errorf("配置引入嵌套深度超过 %d 层", maxIncludeDepth)
 	}
 
 	for _, inc := range cfg.Include {
@@ -174,11 +176,18 @@ func processIncludes(cfg *Config, baseDir string, depth int) error {
 		}
 
 		for _, match := range matches {
+			absMatch, _ := filepath.Abs(match)
+			if visited[absMatch] {
+				return fmt.Errorf("检测到循环引入: %s", absMatch)
+			}
+			visited[absMatch] = true
+
 			info, err := os.Stat(match)
 			if err != nil {
 				return fmt.Errorf("读取引入文件 %q 失败: %w", match, err)
 			}
 			if info.IsDir() {
+				delete(visited, absMatch)
 				continue
 			}
 
@@ -193,7 +202,7 @@ func processIncludes(cfg *Config, baseDir string, depth int) error {
 			}
 
 			if len(included.Include) > 0 {
-				if err := processIncludes(&included, filepath.Dir(match), depth+1); err != nil {
+				if err := processIncludes(&included, filepath.Dir(match), depth+1, visited); err != nil {
 					return err
 				}
 			}
@@ -208,6 +217,8 @@ func processIncludes(cfg *Config, baseDir string, depth int) error {
 					cfg.Variables.Set[k] = v
 				}
 			}
+
+			delete(visited, absMatch)
 		}
 	}
 

internal/config/config_test.go

@@ -4,6 +4,7 @@ package config
 import (
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 )
 
@@ -598,7 +599,7 @@ include:
 		}
 	})
 
-	t.Run("circular include detected", func(t *testing.T) {
+	t.Run("circular include detected immediately", func(t *testing.T) {
 		tmpDir := t.TempDir()
 
 		cfg1 := `
@@ -624,6 +625,81 @@ include:
 		if err == nil {
 			t.Error("expected error for circular include")
 		}
+		if !strings.Contains(err.Error(), "循环引入") {
+			t.Errorf("error should mention circular include, got: %v", err)
+		}
+	})
+
+	t.Run("self include detected", func(t *testing.T) {
+		tmpDir := t.TempDir()
+
+		cfg := `
+servers:
+  - listen: ":8080"
+include:
+  - path: "a.yaml"
+`
+		if err := os.WriteFile(filepath.Join(tmpDir, "a.yaml"), []byte(cfg), 0o644); err != nil {
+			t.Fatal(err)
+		}
+
+		_, err := Load(filepath.Join(tmpDir, "a.yaml"))
+		if err == nil {
+			t.Error("expected error for self include")
+		}
+	})
+
+	t.Run("diamond include works", func(t *testing.T) {
+		tmpDir := t.TempDir()
+
+		mainCfg := `
+servers:
+  - listen: ":8080"
+include:
+  - path: "b.yaml"
+  - path: "c.yaml"
+`
+		bCfg := `
+servers:
+  - listen: ":9090"
+include:
+  - path: "shared.yaml"
+`
+		cCfg := `
+servers:
+  - listen: ":9091"
+include:
+  - path: "shared.yaml"
+`
+		sharedCfg := `
+variables:
+  set:
+    shared: value
+`
+		if err := os.WriteFile(filepath.Join(tmpDir, "config.yaml"), []byte(mainCfg), 0o644); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(filepath.Join(tmpDir, "b.yaml"), []byte(bCfg), 0o644); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(filepath.Join(tmpDir, "c.yaml"), []byte(cCfg), 0o644); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(filepath.Join(tmpDir, "shared.yaml"), []byte(sharedCfg), 0o644); err != nil {
+			t.Fatal(err)
+		}
+
+		cfg, err := Load(filepath.Join(tmpDir, "config.yaml"))
+		if err != nil {
+			t.Fatalf("diamond include should work: %v", err)
+		}
+
+		if len(cfg.Servers) != 3 {
+			t.Errorf("expected 3 servers, got %d", len(cfg.Servers))
+		}
+		if cfg.Variables.Set["shared"] != "value" {
+			t.Error("shared variable should be merged")
+		}
 	})
 
 	t.Run("empty include list is no-op", func(t *testing.T) {

internal/config/defaults.go

@@ -734,6 +734,7 @@ func GenerateConfigYAML(cfg *Config) ([]byte, error) {
 	buf.WriteString("#   - path: \"conf.d/*.yaml\"       # 相对路径 + glob 模式\n")
 	buf.WriteString("#   - path: \"sites/example.yaml\"  # 单个文件引入\n")
 	buf.WriteString("# 支持循环检测和深度限制（最大 10 层）\n")
+	buf.WriteString("# 注意：只有 servers、stream、variables 会被合并，其他字段忽略\n")
 
 	return buf.Bytes(), nil
 }