Cleanup source.dynamic, fix `append` #11597

Job	Run time
build_opam (4.14.x)	25s
build_details	3s
build_js	26s
build_opam (5.2.x)	25s
lezer_parse	26s
tree_sitter_parse	28s
build_no_depopts	14s
build_posix (debian_trixie, amd64)	12s
run_tests (@citest)	14s
build_posix (debian_bookworm, amd64)	13s
run_tests (@doctest)	14s
build_posix (ubuntu_oracular, amd64)	12s
run_tests (@mediatest)	14s
build_win32 (x64)	12s
build_posix (ubuntu_noble, amd64)	13s
build_posix (alpine, amd64)	12s
update_doc	0s
fetch_s3_artifacts	1s
build_docker_minimal	1s
build_docker	1s
build_docker_alpine_minimal	1s
build_docker_alpine	1s
update_release	1s
build_docker_release	1s
build_docker_release-minimal	1s
	4m 31s

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