Simplify double-nested lambdas in command selection. #1693

Job	Run time
json-schema	1m 6s
format	3m 23s
builds / build (windows-2022, windows-ci)	17m 50s
builds / build (ubuntu-20.04, linux-ci)	9m 35s
builds / build (macos-12, macos-ci)	13m 36s
	45m 30s

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