Great! 
If you were to do so perhaps you could checkout this detail within a docker environment (as, having abandoned docker, I cannot be sure what was present in my docker test).
We have both seen a single line roomservice.xml which reads
<project name="LineageOS/android_device_fairphone_FP4" path="device/fairphone/FP4" remote="github" />
No kernel is indicated – got to be a fail.
The log shows:
Looking for dependencies in device/fairphone/FP4
device/fairphone/FP4 has no additional dependencies.
Done
Odd because in /device/fairphone/FP4/lineage.dependencies I see
{
"repository": "android_kernel_fairphone_FP4",
"target_path": "kernel/fairphone/FP4"
}
Of course the script does helpfully pass on
No such item in brunch menu. Try 'breakfast'
But the script seems to have no ability to run breakfast.
In my case by converting to “plain repo sync method” breakfast is more or less required in establishing the build environment.
Secondly,
There is an /e/OS variant FP4.xml published https://gitlab.e.foundation/e/os/local_manifests/-/blob/v1-s/FP4.xml?ref_type=heads.
However using it (with repo sync) I am currently failing at the “writing build rules …” stage with
FAILED:
build/make/core/Makefile:61: error: overriding commands for target `out/target/product/FP4/vendor/bin/hw/android.hardware.biometrics.fingerprint@2.1-service',
previously defined at build/make/core/base_rules.mk:525
11:38:23 ckati failed with: exit status 1
Seems the error was also encountered here Building with Docker image for FP4 fails