I dismantled it all and dug out some deep footings to concrete a decent new post in completely independent of the wall, then I started rebuilding the wall, trying to keep the number of courses matching other parts. I used reclaimed bricks of the same stock to replace the miss matched ones from a previous repair, including the shiny engineering bricks.
I rehung the gate higher up so it stopped dragging on the ground and installed a new latch replacing the old one that had corroded and broken inside.
Now when the gate slams against the post it won’t damage the wall. Long term the hinge side of the gate will need attention and the gate too, but we’ll do this in the spring as there are other projects at this property with more urgency.