  We conducted a comprehensive investigation of the brightest-of-all-time GRB
221009A using new insights from very high energy (VHE) observations from LHAASO
and a complete multiwavelength afterglow dataset. Through data fitting, we
imposed constraints on the jet structure, radiation mechanisms, and burst
environment of GRB 221009A. Our findings reveal a structured jet morphology
characterized by a core+wing configuration. A smooth transition of energy
within the jet takes place between the core and wing, but with a discontinuity
in the bulk Lorentz factor. The jet structure differs from both the case of
short GRB 170817A and the results of numerical simulations for long-duration
bursts. The VHE emission can be explained by the forward-shock synchrotron
self-Compton radiation of the core component, but requiring a distinctive
transition of the burst environment from uniform to wind-like, suggesting the
presence of complex pre-burst mass ejection processes. The low-energy
multiwavelength afterglow is mainly governed by the synchrotron radiation from
the forward and reverse shocks of the wing component. Our analysis indicates a
magnetization factor of 5 for the wing component. Additionally, by comparing
the forward shock parameters of the core and wing components, we find a
potential correlation between the electron acceleration efficiency and both the
Lorentz factor of the shock and the magnetic field equipartition factor. We
discuss the significance of our findings, potential interpretations, and
remaining issues.
