  GJ436b might be the prototype of warm Neptunes that have undergone late
migration induced by an outer companion. Precise determination of the orbital
architecture of such systems is critical to constraining their dynamical
history and evaluating the role of delayed migration in the exoplanet
population. To this purpose we analyzed the Rossiter-McLaughlin (RM) signal of
GJ436 b in two transits - recently observed with ESPRESSO - using three
different techniques. The high level of precision achieved in radial velocity
(RV) measurements allows us to detect the deviation from the Keplerian orbit,
despite the slow rotation of the M dwarf host (vsini = 272.0+40.0-34.0 m/s),
and to measure the sky-projected obliquity ($\lambda$ =
102.5+17.2-18.5$^{\circ}$). The Reloaded RM technique, which allows the stellar
RV field along the transit chord to be analyzed, yields $\lambda$ =
107.5+23.6-19.3$^{\circ}$ and vsini = 292.9+41.9-49.9 m/s. The RM Revolutions
technique, which allows us to fit the spectral profiles from all
planet-occulted regions together, yields $\lambda$ = 114.1+22.8-17.8$^{\circ}$
and vsini = 300.5+45.9-57.0 m/s. The consistent results between these three
techniques, and with published results from HARPS/HARPS-N data, confirm the
polar orbit of GJ436b and support the hypothesis that its origin lies in Kozai
migration. Results from a joint RM Revolutions analysis of the ESPRESSO, HARPS,
and HARPS-N datasets ($\lambda$ = 113.5+23.3-17.3$^{\circ}$; vsini =
293.5+43.7-52.2 m/s) combined with a revised stellar inclination ($i_\star$ =
35.7+5.9-7.6$^{\circ}$ or 144.2+7.6-5.9$^{\circ}$) lead us to constrain the 3D
obliquity $\Psi$ to 103.2+12.8-11.5$^{\circ}$.
