tokens: avoid surplus detokenising #79

Job	Run time
1/4	13m 15s
2/4	12m 29s
3/4	11m 10s
4/4	16m 11s
py-3-latest	18m 32s
flaky	6m 25s
_remote_background_indep_poll	5m 10s
_remote_background_indep_tcp	6m 56s
macos 1/5	24m 26s
macos 2/5	21m 48s
codecov	8s
	2h 16m 30s

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