docs(capi): define stable ABI contract #1343

Job	Run time
agent-record	14s
commit-protocol-tag	14s
cuda-arch-features	11s
build-test-cpu	14m 55s
sanitize-cpu (address,undefined)	21m 10s
documentation-checkpoint	11s
device-leakage	15s
sanitize-cpu (thread)	19m 55s
	57m 5s

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