tp: fix descendant_slice missing boundary instant children #13561

Job	Run time
analyze	11s
ui / ui	5m 35s
fuzzer / fuzzer	2m 19s
android / android	11m 45s
bazel / bazel	3m 10s
linux / linux (clang-x86_64-asan_lsan, is_debug=false is_asan=true is_lsan=true cc_wrapper=\"ccache\")	13m 31s
rust-sdk / rust-sdk	4m 37s
linux / linux (clang-x86_64-msan, is_debug=false is_msan=true cc_wrapper=\"ccache\")	20m 6s
linux / linux (gcc8-x86_64-release, is_debug=false is_clang=false enable_perfetto_grpc=true cc=\"gcc-8\" ...	12m 13s
repo-checks / repo-checks	6m 41s
linux / linux (clang-x86_64-debug, is_debug=true is_hermetic_clang=false non_hermetic_clang_stdlib=\"libc...	23m 48s
linux / linux (clang-x86_64-tsan, is_debug=false is_tsan=true cc_wrapper=\"ccache\")	14m 8s
linux / linux (clang-x86-release, is_debug=false target_cpu=\"x86\" cc_wrapper=\"ccache\")	5m 36s
bigtrace	-1s
ensure-ci-is-green	4s
	2h 3m 43s

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