Pebble flux through the iceline (left axis) and observable cold water vapour mass (right axis) versus time for different dust trap leakiness and parameters. The different colours indicate simulations with δ_turb = 10⁻⁴ and varying viscosity from α_visc = 10⁻³ (most blocking, dark blue) to α_visc = 10⁻² (fully permeable, light blue). We present these four cases because as seen in Fig. 6, varying the viscosity across this column samples well the different leakiness regimes. Note that for weak traps (e.g. with M_p = 30 M_⊕), even the most blocking trap is quite leaky. Grey dots indicate measurements of the vapour reservoir made with JWST (see Figure 2 in Krijt et al. 2025) and converted into pebble flux following Eq. (6). The title of each panel indicates the parameter that is varied from the standard fiducial values: v_frag = 1 m s⁻¹, M_p = 100 M_⊕, a_p = 10 au and M_disc = 0.05 M_⊙. The grey star label and horizontal line indicate an estimate of the error on the disc age (~0.5 Myr, Krijt et al. 2025).