fix: wait out SQLite busy on concurrent asset upserts

Deep mode fires many create_asset calls at once. UpsertAssets used a
DEFERRED transaction (SELECT then INSERT) on a 25-connection pool, so
writers hit SQLITE_BUSY immediately and returned "database is locked"
in a few milliseconds instead of waiting.

Open SQLite with _txlock=immediate and a 30s busy timeout, shrink the
pool, and retry locked upserts. Add a 32-way concurrent upsert test.

internal/database/asset.go

@@ -304,6 +304,16 @@ func appendAssetAccess(query string, args []interface{}, access RBACListAccess,
 }
 
 func (db *DB) UpsertAssets(assets []*Asset, ownerUserID string, allowGlobal ...bool) (AssetImportResult, error) {
+	var result AssetImportResult
+	err := retrySQLiteBusy(8, func() error {
+		var err error
+		result, err = db.upsertAssetsOnce(assets, ownerUserID, allowGlobal...)
+		return err
+	})
+	return result, err
+}
+
+func (db *DB) upsertAssetsOnce(assets []*Asset, ownerUserID string, allowGlobal ...bool) (AssetImportResult, error) {
 	result := AssetImportResult{}
 	tx, err := db.Begin()
 	if err != nil {

internal/database/asset_test.go

@@ -1,9 +1,11 @@
 package database
 
 import (
+	"fmt"
 	"path/filepath"
 	"strconv"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -86,6 +88,39 @@ func TestFofaAssetIgnoresInvalidOptionalStructuredFields(t *testing.T) {
 	}
 }
 
+func TestUpsertAssetsConcurrentDoesNotReturnLocked(t *testing.T) {
+	db, err := NewDB(filepath.Join(t.TempDir(), "assets-concurrent.db"), zap.NewNop())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer db.Close()
+
+	const n = 32
+	errCh := make(chan error, n)
+	var wg sync.WaitGroup
+	for i := 0; i < n; i++ {
+		wg.Add(1)
+		i := i
+		go func() {
+			defer wg.Done()
+			asset := &Asset{Host: fmt.Sprintf("h%d.example.com", i), Port: 443, Protocol: "https", Title: fmt.Sprintf("t%d", i)}
+			_, err := db.UpsertAssets([]*Asset{asset}, "user-a")
+			errCh <- err
+		}()
+	}
+	wg.Wait()
+	close(errCh)
+	for err := range errCh {
+		if err != nil {
+			t.Fatalf("concurrent upsert: %v", err)
+		}
+	}
+	_, total, err := db.ListAssets(100, 0, AssetListFilter{}, RBACListAccess{Scope: RBACScopeAll})
+	if err != nil || total != n {
+		t.Fatalf("want %d assets, got total=%d err=%v", n, total, err)
+	}
+}
+
 func TestAssetUpsertDeduplicatesAndUpdates(t *testing.T) {
 	db, err := NewDB(filepath.Join(t.TempDir(), "assets.db"), zap.NewNop())
 	if err != nil {

internal/database/database.go

@@ -14,9 +14,12 @@ import (
 )
 
 const (
-	// SQLite 在 WAL 模式下建议使用较保守的连接数，降低长读快照导致 checkpoint 饥饿的概率。
-	sqliteMaxOpenConns = 25
-	sqliteMaxIdleConns = 5
+	// WAL 允许并发读，但同一时间仍只有一个写者。连接池过大时，Deep 模式并行
+	// create_asset 会各自 Begin+SELECT 再 INSERT，触发 SQLITE_BUSY（database is locked）
+	// 且 DEFERRED 事务升级写锁时可能立刻失败、不走 busy_timeout。
+	sqliteMaxOpenConns  = 8
+	sqliteMaxIdleConns  = 4
+	sqliteBusyTimeoutMS = 30000
 	// 以页为单位的自动 checkpoint 触发阈值（默认 1000 页，约 4MB @ 4KB/page）。
 	sqliteWALAutoCheckpointPages = 1000
 	// 控制 WAL 目标上限，避免异常场景持续膨胀（256MB）。
@@ -25,9 +28,39 @@ const (
 	sqlitePassiveCheckpointInterval = 300 * time.Second
 )
 
-// configureDBPool 设置 SQLite 连接池参数，提升并发稳定性
+func sqliteOpenDSN(path string) string {
+	return fmt.Sprintf("%s?_journal_mode=WAL&_foreign_keys=1&_busy_timeout=%d&_synchronous=NORMAL&_txlock=immediate", path, sqliteBusyTimeoutMS)
+}
+
+func isSQLiteBusy(err error) bool {
+	if err == nil {
+		return false
+	}
+	msg := strings.ToLower(err.Error())
+	return strings.Contains(msg, "database is locked") || strings.Contains(msg, "sqlite_busy")
+}
+
+func retrySQLiteBusy(attempts int, op func() error) error {
+	if attempts < 1 {
+		attempts = 1
+	}
+	var err error
+	backoff := 5 * time.Millisecond
+	for i := 0; i < attempts; i++ {
+		err = op()
+		if err == nil || !isSQLiteBusy(err) {
+			return err
+		}
+		time.Sleep(backoff)
+		if backoff < 100*time.Millisecond {
+			backoff *= 2
+		}
+	}
+	return err
+}
+
+// configureDBPool 设置 SQLite 连接池：保留少量连接给 WAL 并发读，避免 25 路写连接互锁。
 func configureDBPool(db *sql.DB) {
-	// SQLite 同一时间只允许一个写入者；过高连接数会放大锁竞争和 WAL 回收延迟。
 	db.SetMaxOpenConns(sqliteMaxOpenConns)
 	db.SetMaxIdleConns(sqliteMaxIdleConns)
 	db.SetConnMaxLifetime(30 * time.Minute)
@@ -123,7 +156,7 @@ func (db *DB) runPassiveCheckpoint(trigger string) {
 
 // NewDB 创建数据库连接
 func NewDB(dbPath string, logger *zap.Logger) (*DB, error) {
-	db, err := sql.Open("sqlite3", dbPath+"?_journal_mode=WAL&_foreign_keys=1&_busy_timeout=5000&_synchronous=NORMAL")
+	db, err := sql.Open("sqlite3", sqliteOpenDSN(dbPath))
 	if err != nil {
 		return nil, fmt.Errorf("打开数据库失败: %w", err)
 	}
@@ -210,7 +243,7 @@ func (db *DB) initTables() error {
 
 // NewKnowledgeDB 创建知识库数据库连接（只包含知识库相关的表）
 func NewKnowledgeDB(dbPath string, logger *zap.Logger) (*DB, error) {
-	sqlDB, err := sql.Open("sqlite3", dbPath+"?_journal_mode=WAL&_foreign_keys=1&_busy_timeout=5000&_synchronous=NORMAL")
+	sqlDB, err := sql.Open("sqlite3", sqliteOpenDSN(dbPath))
 	if err != nil {
 		return nil, fmt.Errorf("打开知识库数据库失败: %w", err)
 	}