Check if before source is ready in crossfade before returning it. #11670

Job	Run time
build_js	2m 12s
build_js	2m 12s
build_details	4s
build_details	4s
build_opam (4.14.x)	7m 31s
build_opam (4.14.x)	7m 24s
build_opam (5.2.x)	5m 0s
build_opam (5.2.x)	4m 44s
build_no_depopts	3m 59s
build_no_depopts	4m 24s
lezer_parse	52s
lezer_parse	52s
build_posix (debian_trixie, amd64)	4m 35s
build_posix (debian_trixie, amd64)	4m 39s
build_win32 (x64)	16m 47s
build_win32 (x64)	16m 49s
build_posix (debian_bookworm, amd64)	4m 33s
build_posix (debian_bookworm, amd64)	4m 48s
run_tests (@citest)	4m 25s
run_tests (@citest)	4m 20s
build_posix (ubuntu_oracular, amd64)	5m 31s
build_posix (ubuntu_oracular, amd64)	5m 31s
run_tests (@doctest)	4m 5s
run_tests (@doctest)	4m 31s
build_posix (ubuntu_noble, amd64)	4m 36s
build_posix (ubuntu_noble, amd64)	4m 41s
tree_sitter_parse	50s
tree_sitter_parse	50s
build_posix (alpine, amd64)	6m 45s
build_posix (alpine, amd64)	5m 58s
run_tests (@mediatest)	4m 5s
run_tests (@mediatest)	4m 21s
update_doc	0s
update_doc	0s
fetch_s3_artifacts	0s
fetch_s3_artifacts	0s
build_docker_minimal	0s
build_docker_minimal	0s
build_docker	0s
build_docker	0s
build_docker_alpine	0s
build_docker_alpine	0s
build_docker_alpine_minimal	0s
build_docker_alpine_minimal	0s
build_docker_release	0s
build_docker_release	0s
build_docker_release-minimal	0s
build_docker_release-minimal	0s
update_release	0s
update_release	0s
	2h 31m 58s

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