I confirm that after setting up the firmware from scratch everything works as expected. There are still a couple of things that need to be ironed out but I think they go beyond the scope of this thread as tilt correction works.
Thanks to all who helped, I wish I could buy you each a beer!
Best
@sebkritikel By all means! Bear in mind that I have made no changes of my own beyond what was discussed/posted in this thread (except for the fans but I find that irrelevant given the topic) - in other words, the new firmware is an amalgamation of the code cited here. In any case, I will link all relevant code snippets below in the hopes that they serve someone in the future.
bed.g
M561 ; clear any bed transform
G28 ; home
G30 P0 X105 Y0 Z-99999 ; probe near a leadscrew, half way along Y axis
G30 P1 X105 Y150 Z-99999 S2 ; probe near a leadscrew and calibrate 2 motors
config.g
; General preferences
G90 ; send absolute coordinates...
M83 ; ...but relative extruder moves
M550 P"Printer Extrusions" ; set printer name
M669 K1 ; select CoreXY mode
; Network
M552 S1 ; enable network
M586 P0 S1 ; enable HTTP
M586 P1 S0 ; disable FTP
M586 P2 S0 ; disable Telnet
; Drives
M569 P0 S1 ; physical drive 0 goes forwards
M569 P1 S1 ; physical drive 1 goes forwards
M569 P2 S0 ; physical drive 2 goes backwards
M569 P3 S1 ; physical drive 3 goes forwards
M569 P4 S0 ; physical drive 4 goes backwards
M584 X0 Y1 Z2:4 E3 ; set drive mapping
M671 X105:105 Y0:150 S5 ; leadscrews at left (connected to Z) and right (connected to E1) of X axis
M350 X16 Y16 Z16 E16 I1 ; configure microstepping with interpolation
M92 X80.00 Y80.00 Z80 E456.00 ; set steps per mm
M566 X900.00 Y900.00 Z1.00 E120.00 ; set maximum instantaneous speed changes (mm/min)
M203 X6000.00 Y6000.00 Z1800.00 E1200.00 ; set maximum speeds (mm/min)
M201 X500.00 Y500.00 Z250.00 E250.00 ; set accelerations (mm/s^2)
M906 X1200 Y1200 Z1100 E1100 I30 ; set motor currents (mA) and motor idle factor in per cent
M84 S30 ; Set idle timeout
; Axis Limits
M208 X0 Y0 Z0 S1 ; set axis minima
M208 X210 Y150 Z150 S0 ; set axis maxima
; Endstops
M574 X1 Y1 Z0 S0
; Z-Probe
M558 P8 H10 I1 R1 F600 X0 Y0 Z1
G31 X0 Y0 Z-0.25 P600
; Heaters
M140 H-1 ; disable heated bed
M305 P1 T100000 B4138 R4700 ; set thermistor + ADC parameters for heater 1
M143 H1 S280 ; set temperature limit for heater 1 to 250C
; Fans
M106 P0 S0 I0 F500 H-1 ; set fan 0 value, PWM signal inversion and frequency. Thermostatic control is turned off
M106 P1 S1 I0 F500 H1 T50 ; set fan 1 value, PWM signal inversion and frequency. Thermostatic control is turned on
; Tools
M563 P0 D0 H1 F0 ; define tool 0
G10 P0 X0 Y0 Z0 ; set tool 0 axis offsets
G10 P0 R0 S0 ; set initial tool 0 active and standby temperatures to 0C
; Custom settings are not defined
; Miscellaneous
T0 ; select first tool
homeall.g
;Home X and Y
G91 ; relative positioning
G1 Z5 F420 H2 ; Lower bed 5mm to ensure it is below the switch trigger height
M400
M913 X50 Y50 ; set X Y motors to 50% of their normal current for homing
G1 H1 X-375 Y-305 F600 ; course home X or Y
G1 H1 X-375 F600 ; course home X
G1 H1 Y-305 F600 ; course home Y
G1 X5 Y5 F600 ; move away from the endstops
G1 H1 X-10 F200 ; fine home X
G1 H1 Y-10 F200 ; fine home Y
G1 X5 Y5 F600 ; go to origin
M400
M913 X100 Y100 ; set X Y motors to 100% of their normal current
;Home Z
G90 ; absolute positioning
G1 X100 Y50 F600 ; go to first probe point
G30 ; home Z by probing the bed
G91 ; relative positioning
G1 Z5 F420 ; lift Z relative to current position
G90 ; absolute positioning
;Load height map
G29 S1
Thanks! Apparently, I wasn't understanding the code fully.
Anyway, I have implemented both of your suggestions and both work. I will stick to the latter one as I find it to be more elegant.
I'm pasting the resulting end gcode in the hopes that it will be useful to somebody:
G1 E-2 F1800; retract
G91; relative positioning
G1 Z5 F1800 ; lift Z relative to current position
G90; absolute positioning
G1 X5 F6000; move to X min
G1 Y5 F6000; move to Y min
G1 Z150 F1800; move to Z max
G10 R0 S0; turn extruder heater off
M291 P"Do you want to cooldown the printer?" S3
G10 R45 S45; set extruder temp to 50C
M106 S255; turn part-cooling fan on
M116 S5; wait
G10 R0 S0; turn extruder heater off
M106 S0; turn part-cooling fan off
Thanks for your input!