Fiscal Intermediaries, Transfer Delivery, and Sustainable Local Growth: Evidence from China’s Province-Managed-County Reform

County economic growth in multi-tiered fiscal systems depends not only on the volume of transfers but also on whether those transfers pass through intermediary governments. This paper separates administrative delegation from fiscal chain redesign in province-managed county reforms in China. We study 1537 counties from 2000 to 2023 and compare D2, which creates direct province–county fiscal accounts, with D1, which delegates administrative authority but keeps the prefectural intermediary. The empirical design uses panel difference-in-differences estimators, synthetic difference-in-differences, double machine learning robustness checks, and exploratory heterogeneity diagnostics. Based on a placebo-corrected lower bound and a cross-estimator upper bound, D2 is associated with a conservative growth range of 0.35 to 1.0 percentage points per year, while the D1 estimate is imprecise. D2 is also associated with higher contemporaneous per capita fiscal expenditure, but the one-year lagged mediator check does not support a fully identified expenditure mechanism. Heterogeneity patterns are consistent with stronger effects in transfer-dependent counties, but they remain exploratory. The outcome is county economic growth, not a composite sustainability index. The results support a focused governance claim. More reliable transfer delivery is consistent with improved local growth capacity, while fiscal, social, and environmental sustainability remain outside the measured outcome space.