Cleanup source.dynamic, fix `append` #11600

Job	Run time
build_details	4s
build_opam (4.14.x)	8m 43s
build_js	2m 1s
build_opam (5.2.x)	5m 12s
build_win32 (x64)	17m 30s
build_no_depopts	5m 53s
build_posix (debian_trixie, amd64)	13m 27s
lezer_parse	52s
build_posix (debian_bookworm, amd64)	13m 55s
run_tests (@citest)	12m 21s
tree_sitter_parse	48s
run_tests (@doctest)	7m 42s
run_tests (@mediatest)	11m 56s
build_posix (ubuntu_oracular, amd64)	14m 24s
build_posix (ubuntu_noble, amd64)	14m 0s
update_doc	0s
build_posix (alpine, amd64)	1m 24s
fetch_s3_artifacts	0s
build_docker_minimal	0s
build_docker_alpine	0s
build_docker	0s
build_docker_alpine_minimal	0s
build_docker_release-minimal	0s
build_docker_release	0s
update_release	0s
	2h 10m 12s

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