runtime.json specifies the expected command-line interface a runtime must provide. However, that minimal CLI does not match the (much more featureful) CLI provided by the reference implementation: runc.
Since (as of v1.11) runc is now used by docker (via containerd), it seems unlikely docker would want to remove functionality simply to align with runtime.md.
Note further that runc's CLI does not align with runtime.md either. The spec says runc should be invoked like this to start a container:
$runtime start <container-id> <path-to-bundle>
... and yet runc actually uses:
runc start [ -b bundle ] <container-id>
The spec states that a "stop" verb is required, but runc has none.
Please clarify what the full, required, runtime CLI should be as the current situation is confusing.
(Currently, I fear we're at the point that the implementation (runc) trumps the spec as defining expected behaviour given that to run under containerd requires a runtime to implement runc's vision of how it should be done, not what the spec [currently] says :-( ).