Cleanup source.dynamic, fix `append` #11603

Job	Run time
build_details	3s
build_js	1m 59s
build_opam (4.14.x)	2m 14s
build_opam (5.2.x)	2m 14s
lezer_parse	51s
tree_sitter_parse	49s
build_no_depopts	1m 53s
build_posix (debian_trixie, amd64)	1m 52s
build_win32 (x64)	1m 52s
build_posix (debian_bookworm, amd64)	1m 51s
run_tests (@citest)	1m 54s
build_posix (ubuntu_oracular, amd64)	1m 51s
run_tests (@doctest)	1m 52s
run_tests (@mediatest)	1m 52s
build_posix (ubuntu_noble, amd64)	1m 51s
update_doc	0s
build_posix (alpine, amd64)	1m 53s
fetch_s3_artifacts	1s
build_docker_alpine	1s
build_docker	1s
update_release	1s
build_docker_alpine_minimal	1s
build_docker_minimal	1s
build_docker_release	1s
build_docker_release-minimal	1s
	26m 59s

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