Htykuut

In the paticcasamuppada's formulation of the twelve nidanas, vedana precedes tanha.

As far as I currently understand, vedana is just the physiological and psychological -and involuntary- response
(felt as a pleasent, unpleasent or neutral sensation) to an specific stimulus. Vedana by itself shouldn't be an enough condition to give rise to tanha, because there's no necessarily an evaluation (sañña) of that feeling that could lead to the rise of a preference (like, dislike or neither-like-nor-dislike), and consequently, to the rise of tanha.

If read in this fashion, shouldn't be sañña placed between vedana and tanha?

Thanks in beforehand.

In paticcasamuppada, shouldn't sañña precede tanha, instead of vedana?

It should and it does: vedana => sañña => vitakka => papanca.

From Madhupindika Sutta (MN 18):

With contact as a requisite condition, there is feeling (vedana). What one feels, one perceives (sañña). What one perceives, one thinks (vitakka) about. What one thinks about, one objectifies (papanca).

To clarify terms, vedana is the qualitative component of the experience of subjective contact with a subjectively delineated (mental representation of) object: "this object feels right" / "this object feels wrong" / "this object feels neither right nor wrong".

Sañña is recognition/classification/delineation of a (subjective notion of) object by the raw features (signs) available to direct observation. While described as a single step, in actuality it is a chain of inferences that evaluates the signs, puts forward hypotheses about the perceived entity and feeds back to seeking more signs to confirm the hypothesis. At the advanced phases of the inference chain, sañña reaches a level of abstraction when it can be described as "conceptualization".

Vitakka (in this context) is pondering or mulling over. It is bringing the attention again and again to a given idea.

Papanca is entering a relationship of "pursuer & pursued" (or acquirer and acquired) with regard to an object. It is objectifying something and making it one's goal (-- and implicitly, making oneself an agent of pursuit. This is out of scope for this question but this is exactly how bhava or "becoming a personal form of existence" comes to fruition).

So, first we delineate an object, then we attribute pleasant experience to a contact with the object, then we conceptualize this experience of contact and the resulting feeling and make it into a target we'd like to acquire.

Vedana and Sanna are conjoined not disjoint.
When it says Vedan it implies there is Sanna as well.

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"Feeling, perception, & consciousness, friend: Are these qualities conjoined or disjoined? Is it possible, having separated them one from another, to delineate the difference among them?"

"Feeling, perception, & consciousness are conjoined, friend, not disjoined. It is not possible, having separated them one from another, to delineate the difference among them. For what one feels, that one perceives. What one perceives, that one cognizes. Therefore these qualities are conjoined, not disjoined, and it is not possible, having separated them one from another, to delineate the difference among them."

https://www.accesstoinsight.org/tipitaka/mn/mn.043.than.html

shouldn't be sañña placed between vedana and tanha?

Vedana & sanna are co-joined (MN 43). They are the mind conditioner (citta sankhara - MN 44).

As far as I currently understand, vedana is just the physiological and
psychological -and involuntary- response (felt as a pleasent,
unpleasent or neutral sensation) to an specific stimulus. Vedana by
itself shouldn't be an enough condition to give rise to tanha,

Vedana alone is enough to give rise to craving. Surely the immediate taste of certain foods is sufficient to give rise to craving. Or surely the sight of certain forms is sufficient to give rise to attraction (which is craving). For example, surely there are all sorts of chemical, hormones & neurological design that gives rise to sexual attraction on a non-verbal or non-thinking level.

there's no necessarily an evaluation (sañña) of that feeling that
could lead to the rise of a preference (like, dislike or
neither-like-nor-dislike), and consequently, to the rise of tanha.

Sanna is not evaluation. Nor is sanna "like & dislike". "Like" & "dislike" are craving; even attachment (abhinandi; found in the definition of the 2nd noble truth). Evaluation of "good" & "bad" are views & opinions attachment (diṭṭhupādānaṃ). Ideas such as "beautiful" are called "themes" ("nimitta"). MN 38 says "delight (nandi) in feelings is attachment".

Engaged as he is in favouring and opposing, whatever feeling he feels—whether pleasant or painful or neither-painful-nor-pleasant—he
delights in that feeling, welcomes it, and remains holding to it. As
he does so, delight arises in him. Now delight in feelings is
clinging. With his clinging as condition, being comes to be; with
being as condition, birth; with birth as condition, ageing and death,
sorrow, lamentation, pain, grief, and despair come to be. Such is the
origin of this whole mass of suffering.

Having thus abandoned favouring and opposing, whatever feeling he feels, whether pleasant or painful or neither-painful-nor-pleasant, he
does not delight in that feeling, welcome it, or remain holding to it.
As he does not do so, delight in feelings ceases in him. With the
cessation of his delight comes cessation of clinging; with the
cessation of clinging, cessation of being; with the cessation of
being, cessation of birth; with the cessation of birth, ageing and
death, sorrow, lamentation, pain, grief, and despair cease. Such is
the cessation of this whole mass of suffering.

MN 38

In terms of sankharas, Sanna and vedanna are citta sankharas and as usual, sankharas stems from ignorance (like asavas) and the rest of what is conditioned stems from contact and dukkha form craving.
https://www.accesstoinsight.org/tipitaka/sn/sn36/sn36.011.than.html
http://obo.genaud.net/dhamma-vinaya/pts/sn/04_salv/sn04.36.015.wood.pts.htm

Since sanna and vedana are citta sankharas, qualifying them of physiological is not a good idea. Same thing with trying to separate them. TYpically, the higher realm have vedana and sanna, without having the 4 elements, meaning without rupa.

Ignorance and contact are the two main conditions that must be stopped. Craving conditions dukkha.
Most of the stuff in the dependent origination depends on contact, more than ignorance and craving.

You say that vedana cannot lead to tanha, by using some proof by contradiction and the concept of necessity. On the contrary. Vedana like you know is typically pleasant, non-pleasant and nor pleasant nor dis-pleasant [typically in 4th jhana]. SO that's the ideal basis for craving to pop up. Once there is a pleasant vedana, there is typically delight,and anybody wants more pleasant vedana.

"Brethren, if there were not this satisfaction which comes from
scents, beings would not lust after scents.

But inasmuch as there is satisfaction in scents, therefore beings lust
after scents.

If misery, Brethren, pertained not to scents, beings would not be
repelled by scents.

But inasmuch as there is misery in scents, beings are repelled by
scents.

If there were no way of escape from scents, beings could not escape
from scents.

But inasmuch as there is a way of escape from scents, beings do escape
from scents.
http://obo.genaud.net/dhamma-vinaya/pts/sn/04_salv/sn04.35.018.wood.pts.htm#p1

the buddha even says how to see the 3 vedanas, in order to progress on the path

One who has seen the pleasant as painful And the painful as a dart,

Seen as impermanent the peaceful feeling Neither painful nor pleasant:

He is a bhikkhu who sees rightly, One who fully understands feelings.

But vedana is conditioned by contact, not by craving,
https://www.accesstoinsight.org/tipitaka/sn/sn36/sn36.023.than.html

and once there is vedena, there is craving, and craving is the ''patipada[=path] to vedana''.
Just like the noble path is the cessation of dukkha, the opposite of noble path that is tanha is the path to contact, which is the condition for the arising of vedana [you do not need to do anything than craving more to get more vedana through contact]. craving as a path is really a super simple path: the path is just craving.
On the contrary, the opposite of craving-as-path has plenty of branches, from right discernment to the stilling of the Sankharas to their destruction.

Puthujjanas who love the idea that there can be perception without vedana are the rationalists. They love to call such a fantasy ''the objective perception'' and they always say that vedana pollutes the knowledge, the perception and the reality [puthujjanas who are rationalist say that the reality is the objects living in a world devoid of humans]. Those people say that the pinnacle of being a human is to be a free thinker, meaning a thinker who is not influenced by other humans, nor swayed by emotions, devoid of biases.
Of course, the dhamma has nothing to do, nor by goals nor methods, with the moronic fantasy of the rationalists.

If you want to know more, there is a whole vagga on khandas, on nidana, on Salayatana and there is a whole Samyutta on vedana

http://obo.genaud.net/backmatter/indexes/sutta/sn/idx_samyutta_nikaya.htm

Typically this stuff is what the sutta in Saɱyutta Nikāya are about. Sadly, not many monks talk about them in a systematic manner. Bikkhu bodhi has done MN and is in the middle of AN right now, so it will be at least one year before he finishes AN, and perhaps he will do DN or Kn before SN.

Another famous bikkhu did an exposition on SN, but also MN, KN and DN, Bhante Dhammavuddho

https://www.youtube.com/user/vbgnet98/playlists?disable_polymer=1

you can get the records of his readings here
http://www.vbgnet.org/resource-audio.asp?page=7&cbbAuthor=&cbbLanguage=2143&cbbSortBy=Title&btnSubmit=Go