wrap speculative mode around bounds computation #12420

Job	Run time
extraction	0s
gobview (ubuntu-22.04, ocaml-variants.4.14.2+options,ocaml-option-flambda, 14)	7m 37s
regression (ubuntu-22.04, ocaml-variants.4.14.2+options,ocaml-option-flambda)	8m 6s
regression (macos-13, ocaml-variants.4.14.2+options,ocaml-option-flambda)	24m 12s
	39m 55s

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