adrianschmutzler:

Based on my research, it appears the "fat" image was the result of a hack to make use of the entire flash for this device, since the vendor put the caldata at 0x660000 and therefore limited the size of the firmware image.

cameo_ap94_mtdlayout=mtdparts=spi0.0:256k(uboot)ro,64k(config)ro,6208k(firmware),64k(caldata)ro,1600k(unknown)ro,64k@0x7f0000(caldata_copy)
cameo_ap94_mtdlayout_fat=mtdparts=spi0.0:256k(uboot)ro,64k(config)ro,7808k(firmware),64k(caldata)ro,64k@0x660000(caldata_orig),6208k@0x50000(firmware_orig)

This was accompanied by providing a whole set of images to flash from one variant to another, which was dropped again here:
9a11f88

From my perspective, this is an ugly hack that has been abandoned when adding this device to ath79 for a good reason, where only the "correct" vendor partitioning was implemented.

Since the copied caldata of the previous "fat" image appears to be in the read-only region of the flash for the new image, it should be relatively simple to migrate to ath79:

1. flash the ath79 image
2. install kmod-mtd-rw via opkg (or built it into the image directly)
3. enable kmod-mtd-rw
4. remove ro for the "real" caldata partition and copy the contents from the previously copied partition at 0x7f0000 back to their proper location
5. reboot the device, put ro back, and remove kmod-mtd-rw

Regarding the factory image:
I took a quick dive into that terribly image/legacy.mk code, and as it appears, the factory image is created by just appending "00AP94-AR7161-RT-080619-00" to the sysupgrade image after padding:

		( \
			dd if=$(call sysupname,$(1),$(2)) bs=4096k conv=sync; \
			echo -n "$(7)"; \
		) > $(call factoryname,$(1),$(2)); \

$(7) should be the string given above here.

For ath79, I can tell that no factory image has been set up in the first place. If that's required for factory flashing, somebody would need to add it, though that might be relatively trivial based on the information above.

DarkCraz:

"From my perspective, this is an ugly hack that has been abandoned when adding this device to ath79 for a good reason, where only the "correct" vendor partitioning was implemented."

Without this "ugly" hack, the stock image is useless because it is impossible to install the minimum required packages to go to extroot or extoverlay. Extoverlay minimum instalation require such packets as block-mount, e2fsprogs, kmod-fs-ext4, kmod-usb-storage. Free space ends already after the installation of e2fsprogs&kmod-fs-ext4. Thats why this hack need to be reimplemented. Stock flash layot Is suitable for use with stock firmware, but not with openwrt.