Top: time evolution of the mass-weighted [Fe/H] of the gaseous corona as a function of lookback time, with linestyles indicating the average metallicity within successive radial cuts (gas within |z| < 2 kpc was excluded to avoid contamination from the disc): r ≤ 0.1R_200,c, r ≤ 0.2R_200,c, r ≤ 0.5R_200,c, and the entire corona. Bottom: density of forming stars as a function of formation time (x-axis) and galactocentric radius r (y-axis), with red indicating higher and blue lower densities. This highlights both the inside-out growth of the disc and the orbits of gas-rich merger events. The black line traces the virial radius R_200,c as a function of look-back time.