Transitivity of the verb "undertake"

It seems obvious that undertake is intransitive in such sentences as

undertake to learn to swim

State senators undertook to use federal funds for improving schools.

To join the club, you have to undertake to buy a minimum of six books a year.

However, this is belied by several dictionary sources, including Merriam Webster and Macmillan, which define the verb along with this usage as transitive. Why is that?

If the verb is intransitive, then the senators merely undertook. Period. That doesn’t sound right. You have to undertake something. It takes an object and so is therefore transitive.

OLD gives these three transitive examples:

• A firm of builders undertook the construction work. (DO = noun phrase)
• The firm undertook to keep price increases to a minimum. (DO = infinitive clause)
• Truck driver implicitly undertakes that he is reasonably skilled as a driver. (DO = noun complement clause)

It doesn’t matter whether the direct object is a noun phrase or pronoun, a non-finite verb clause like an infinitive or a gerund, or a noun complement clause joined by things like that or whether, it’s still the syntactic constituent that is acting as the direct object.

And so the verb must therefore still be transitive in all three such cases.