Understanding Saṅkhāra in dependent origination as *choices* of body, speech and mind?

The involvement of intention need not be ones own:

DN33:1.11.171: Four kinds of reincarnation. There is a reincarnation where only one’s own intention is effective, not that of others. There is a reincarnation where only the intention of others is effective, not one’s own. There is a reincarnation where both one’s own and others’ intentions are effective. There is a reincarnation where neither one’s own nor others’ intentions are effective.

If we are awoken and killed by robbers in our own homes and horrified by that killing, then that kamma is driven by the intentions of others interacting with our own underlying clinging to life.

This example is a bit dramatic but it points out the fallacy that intention arises locally out of self. Therefore our experiments must include acceptance of what is experienced without underlying tendencies.

Creation of Sankara - Mental Formation only through - Thought, Words and Action with clinging (Upaadana) to create cause (karma) if equanimity no Karma created.

Paticca Samupada (D.O.) - only after feeling - craving it moves to Jaana stage where Sankara upaadaana creates Karma -

Consciousness - no continuation

Anicca = nothing is permanent therefore nothing continues There is no re-incarnation in Budhha Dharma - it is re-birth process

What method of meditation you practise and the Kamatahan you received from your teacher? Anyway, all kinds of thoughts arise during meditative practice but that is natural, as long as you know and acknowledge each thought and get back to your main breathing meditation - you will go through four stages if you are practicing Sati Pattana

For your information no waves are accumulated... they are impressions only. Nama - Rupa cannot generate Sankara... Sankara is created only from Mental Formation aggregate... Nama Rupa is basically Mind+ Body which arises after consciousness in D.O. The five aggregates arise with Craving...and \Sankara to create Karma it would have to be Sankaara with Upaadana, because even Arahant can have sankaara but that is with equanimity and those Sankaaras do not create Karma (cause)

Hope these answers would help you

skilled practitioners

Yes.

The second nidana of D.O. is commonly translated as 'volitional factors' or 'choices'

The above is wrong. "Volition" is 1st mentioned at nama-rupa.

There are three kinds of choices. Choices by way of body, speech, and mind. These are called choices.

The Pali is kaya, vaci & citta sankhara, which are defined in MN 44 as in & out breathing; initial & sustained thought; and perception & feeling.

Breathing conditions the state of the body = kaya sankharo = body conditioner.

Thought conditions speech = vaci sankharo = verbal conditioner.

Perception & feeling condition the state of the mind = citta sankhara = mind conditioner.

I've detected that maybe not all skilled practitioners on this forum agree that this is an accurate translation?

D.O. was hijacked to create a theory of reincarnation to provide moral teachings to people. Not all practitioners teach D.O. the same because some monks deliberately don't teach the truth but teach skillful means.

It has been suggested that the best means of figuring this out - as the Buddha instructed! - is to put it to empirical test in personal meditation practice.

Yes. My explanation accords with meditation practice.

I've found support for the proposition that not all Saṅkhāra is intentional from SN 12.38:

The above is irrelevant because it is not about the 2nd condition sankhara. It is about "becoming" or "patiṭṭhā viññāṇa", similar to AN 3.76. It says:

When consciousness is established and grows, there is production of a new state of existence (bhavā) in the future.

Note: Bhikkhu Sujato translations are often ignored by serious scholars; particularly anything about dependent origination.

Second, what is the proper translation? ... assuming there is disagreement that 'accumulated tendencies' is the proper translation - even though it omits the connotation of choice. Could it simply be 'actions resulting from ignorance?'

You are bouncing too far ahead, from ignorance to kamma. Kamma does not occur until volition, which starts at nama-rupa and then starts again at attachment.

The word "anusaya" means "underlying tendencies" and is often mentioned after contact, such as in MN 148. My point is the use of the word "anusaya" does not indicate any of the specific 12 conditions.

While "anusaya" is part of ignorance; the word "anusaya" is used in different places in the teachings.

Third, is it proper to think of the labored breathing that comes from the arising of disturbing emotions as Saṅkhāra? It does seem to me to be non-volitional... Is this right?

Correct. This is the correct view of kaya-sankhara, as confirmed by meditation.

Fourth, is it an accumulated tendency?

No. The underlying tendencies are part of ignorance (AN 7.11). They "asava" or "flow out" at ignorance (MN 9). They cause the breathing (kaya sankhara) to become laboured and also can trigger discursive thoughts & memories (vaci & citta sankhara).

Perhaps some Saṅkhāra are accumulated habits

No. Please do not use Mahayana to interpret Pali. Nagarjuna was wrong about sankhara, the same as most Theravada commentators are wrong.

"Accumulated tendencies", which is an energetic drive, form part of ignorance. The "sankhara" they trigger may be classed as "habitual thoughts" however the underlying drive or tendency is part of ignorance.

In meditation, when you crush a discursive thought, the pulsating energy can still remain.

The discursive thought is "sankhara". The pulsating underlying energy is part of "ignorance", as clearly described in MN 9. Read MN 9, the very end of the sutta.

that may involve some measure of choice

No. There is no choice at sankhara. Sankhara is the opposite. It is non-choice. The choice occurs at nama-rupa, when nama-rupa feels, perceives & has contact with the sankhara. Refer to MN 19, which clearly describes how Buddha made a choice to end the discursive thoughts.

and some are simply non-volitional

Sankhara are non-volitional.

and have nothing to do with 'accumulation' per se?

Not all underlying tendencies are "accumulated" from the past. Some underlying tendencies are in-born (refer to MN 64, beginning of sutta).

The labored breathing or change in breathing that comes involuntarily from the arising of disturbing emotions...

Yes!

the fact of it itself does not seem to me to be accumulated?

The ignorant emotion may be accumulated and "stored". But the sankhara is not accumulated. Each sankhara is a new sankhara.

Perhaps the 'accumulation' refers to some aspect of it -

Pali does not use the term "accumulated". Forget this term.

Fifth, it's been suggested that when one attains a certain proficiency in meditation the true definition of Saṅkhāra can be seen

Indeed.

but what level of proficiency is necessary to reveal the truth and in what form of meditation?

Clear mind established in breathing.

Clear mind must be able to see the arise of discursive thoughts out of relative empty or thoughtless mind.

Visualizing the experiment... I imagine one must be able to calm the mind to a sufficient degree that one can witness the waves generated when a disturbing emotion arises

Yes!

in much the same way we are easily be able to notice the waves generated when a rock hits a still pond.

Yes!

The waves would be the Saṅkhāra (some action of breath or speech or mind?)

Waves are formed by energy. The energy is from ignorance. The waves are sankhara.

Its not "action". Its "motion" of breath, thought or feeling/perception.

and the question would be whether there was choice involved

There is no choice at this level. You should already understand when distracting thoughts arise in meditation (when you want to concentrate) they are not a "choice".

or if any aspect of the wave was a characteristic reinforced through accumulation?

No. They are not reinforced at "sankhara".

They are reinforced at nama-rupa, when nama "chooses" to give "attention" to those sankhara. Remember, "nama" is "feeling, perception, intention/choice, contact & attention".

Again, read MN 19, the part where the Buddha mentions "inclination of mind". The word "inclination" is "namati", the verb of "nama".

The ignorant sankhara is either reinforced at nama-rupa, by giving attention to the ignorant sankhara; or, otherwise, the ignorant sankhara is cut & stopped at nama-rupa.

Help or ideas appreciated!

Study very carefully or meditatively page 3 to 6 of this link: Shape of Suffering by Bhikkhu Thanissaro.

Or read my blog: Dependent origination: Namarupa and here: Dependent origination: Sankhara