fix: 修复大规模数据性能与流式状态清理

internal/repository/sqlite_usage.go

@@ -59,6 +59,8 @@ CREATE TABLE IF NOT EXISTS usage_records (
 CREATE INDEX IF NOT EXISTS idx_usage_records_requested_at ON usage_records(requested_at DESC, id DESC);
 CREATE UNIQUE INDEX IF NOT EXISTS idx_usage_records_execution_id ON usage_records(execution_id) WHERE execution_id <> '';
 CREATE INDEX IF NOT EXISTS idx_usage_records_model ON usage_records(model COLLATE NOCASE) WHERE model <> '';
+CREATE INDEX IF NOT EXISTS idx_usage_records_missing_cost_model
+ON usage_records(model COLLATE NOCASE, id) WHERE cost_micros IS NULL;
 
 CREATE TABLE IF NOT EXISTS request_records (
     request_id TEXT PRIMARY KEY,
@@ -234,9 +236,10 @@ const (
 	orphanLifecycleTieWindow = time.Millisecond
 )
 
-// SQLiteUsageRepository 使用单写连接保存全部用量记录。
+// SQLiteUsageRepository 使用单写连接保存事实，并用独立连接池承载只读查询。
 type SQLiteUsageRepository struct {
-	db *sql.DB
+	db     *sql.DB
+	readDB *sql.DB
 }
 
 func OpenSQLiteUsage(databasePath string) (*SQLiteUsageRepository, error) {
@@ -301,6 +304,19 @@ SELECT k.id, 1, k.created_at, 0, 0 FROM managed_keys k`); err != nil {
 		_ = db.Close()
 		return nil, err
 	}
+	readDB, err := sql.Open("sqlite3", dsn)
+	if err != nil {
+		_ = db.Close()
+		return nil, fmt.Errorf("打开 SQLite 只读连接池: %w", err)
+	}
+	readDB.SetMaxOpenConns(4)
+	readDB.SetMaxIdleConns(4)
+	if err := readDB.Ping(); err != nil {
+		_ = readDB.Close()
+		_ = db.Close()
+		return nil, fmt.Errorf("连接 SQLite 只读连接池: %w", err)
+	}
+	repository.readDB = readDB
 	return repository, nil
 }
 
@@ -516,7 +532,7 @@ func (r *SQLiteUsageRepository) ListRecent(ctx context.Context, limit int) ([]co
 	if scanLimit < limit {
 		scanLimit = limit
 	}
-	rows, err := r.db.QueryContext(ctx, `
+	rows, err := r.readDB.QueryContext(ctx, `
 WITH combined AS (
     SELECT
         u.managed_key_id, u.request_id, u.execution_id, COALESCE(NULLIF(u.trace_id, ''), r.trace_id, '') AS trace_id,
@@ -738,5 +754,9 @@ func mergeLifecycleIntoUsage(usage, lifecycle collection.Record) collection.Reco
 }
 
 func (r *SQLiteUsageRepository) Close() error {
-	return r.db.Close()
+	var readErr error
+	if r.readDB != nil {
+		readErr = r.readDB.Close()
+	}
+	return errors.Join(readErr, r.db.Close())
 }