So it’s not disk space: I freed up some space and re-ran the build: it got to the same point and failed again. The interesting bits of the log:
[ 97% 111042/113405] //frameworks/base:test-api-stubs-docs Metalava [common]
FAILED: out/soong/.intermediates/frameworks/base/test-api-stubs-docs/android_common/test-api-stubs-docs-stubs.srcjar out/soong/.intermediates/frameworks/base/test-api-stubs-docs/android_common/test-api-stubs-docs_api.txt out/soong/.intermediates/frameworks/base/test-api-stubs-docs/android_common/test-api-stubs-docs_removed.txt out/soong/.intermediates/frameworks/base/test-api-stubs-docs/android_common/test-api-stubs-docs_annotations.zip out/soong/.intermediates/frameworks/base/test-api-stubs-docs/android_common/api-versions.xml
rm -rf "out/soong/.intermediates/frameworks/base/test-api-stubs-docs/android_common/out"
...
<snip> a long list of filenames being removed
...
Killed
[ 97% 111043/113405] //frameworks/base:hiddenapi-lists-docs Metalava [common]
[ 97% 111044/113405] //frameworks/base:api-stubs-docs Metalava [common]
[ 97% 111045/113405] //frameworks/base:system-api-stubs-docs Metalava [common]
ninja: build stopped: subcommand failed.
19:58:41 ninja failed with: exit status 1
#### failed to build some targets (04:47:19 (hh:mm:ss)) ####
Full error details at https://pastebin.com/8cQb7qWb
So I’ll leave this build for now, and tomorrow I’ll have a try at building a Q /e/ ROM without Docker