There's no path where nodes add themselves to HoudiniAssetInput node inputs using addDownstreamAsset. As such, the automatic downstream cooking and cook on transform change become meaningless for input assets.
In general, I find it a bit strange that not all houdini assets are building depencencies when setting node references, since that's a pre-requisite for downstream cooking working.
There's no path where nodes add themselves to HoudiniAssetInput node inputs using addDownstreamAsset. As such, the automatic downstream cooking and cook on transform change become meaningless for input assets.
https://github.com/sideeffects/HoudiniEngineForUnity/blob/f3cded3b8f8bd18e8fa523891b45e5768c3809e4/Assets/Houdini/Scripts/HoudiniParms.cs#L536
In general, I find it a bit strange that not all houdini assets are building depencencies when setting node references, since that's a pre-requisite for downstream cooking working.