from AN 4.41 samadhi-bhavana sutta (b.bodhi trans.)
(3) “And what is the development of concentration that leads to
mindfulness and clear comprehension? Here, a bhikkhu knows feelings as
they arise, as they remain present, as they disappear; he knows
perceptions as they arise, as they remain present, as they disappear; he
knows thoughts as they arise, as they remain present, as they
disappear.720 This is the development of concentration that leads to mindfulness and clear comprehension.
this is similar to MN 111 anupada (one after another sutta) where sariputta is doing that while IN first jhana, second, third jhana, etc. and the smoking gun is that it’s only in the attainment of the na-sanna-na-asanna-ayatana (neither perception nor non perception dimension) and sanna-vedita-nirodha attainment that one has to emerge from that attainment to be able to reflect and examine what happened during the attainment
the same “sato and sampajanno” is part of the standard 3rd jhana formula.
also in AN 9.36 jhana sutta, one can do the same contemplations on the 5 aggregates and attain nibbana while IN jhana.
in the cook sutta SN 47.8 (a few posts above i quote pali/english and give detailed comments) satipatthana and samadhi are happening at the same time.
in MN 78, we have a detailed process of samadhi development, with a noticable omission of 1st jhana and skipping directly to 2nd jhana, but if you look carefully and make appropriate inferences, it’s making the same point as the goldsmith simile sutta (AN 3.102 ) regarding what kind of skillful thinking is happening while IN first jhana (basically vitakka synonymous with the 3 kinds of samma sankappo )
one of samma sankappo is abyapada, which any of the 4 brahmaviharas qualify under. the standard 4BV formula all include "vipulena, mahaggatena, a-byapajjena.
so it’s pretty safe to infer from this sutta MN 78 at the very least first jhana can be done at the same time as a brahma vihara
and in AN 8.63
all 4 brahmaviharas are explicitly referred to as types of samadhi.
same with 4 satipatthanas.
and here all of those 8 samadhis can be done with (b.bodhi trans.)" with thought and examination; you should develop it without thought but
with examination only; you should develop it without thought and
examination. You should develop it with rapture; you should develop it
without rapture; you should develop it accompanied by comfort; and you
should develop it accompanied by equanimity.
somewhere in sambojjhanga samyutta and in other places, 4 brahmaviharas are linked to 4 formless attainments.
i have no problem with the statement that in meditation contexts samadhi is always equivalent with jhana, but that’s because i understand jhana in a broader sense than ajahn brahm, using the occams razor straightforward reading of the suttas where vitakka and vicara mean thinking and evaluation, kaya means anatomical body.
so in third jhana standard formula, “sukhanca kayena patisamvediti”, sukha is experienced in anatomical body simultaneously while one is contemplating cause, rise, fall of the 5 aggregates with the "sato sampajanno part of standrd 3rd jhana formula) described in AN 4.41.
i don’t believe the goldsmith simile sutta (AN 3.100 ) is a one off situation saying something unusual from the 99% of the suttas. in the standard definition of first jhana and second jhana, it is only in second jhana where the specialized terms “ekodi-bhavan, samadhi-jam piti-sukham” first appear. standard first jhana formula is described as “vivekajam, piti-sukham”, effectively making the same point as AN 3.100 in a concise way: that is, first jhana is weak, the buddha won’t even deign to call it “samadhi”, you have to wait till vitakka and vicara to drop out in second jhana before its worthy of being called samadhi.
ajahn brahm’s definition of first jhana is that you can’t hear sounds, your body has disappeared, you can’t think until after you’ve emerged from that samadhi, contrary to AN 9.36 and MN 111 (and one or 2 more suttas) where only the 8th and 9th samadhi attainments requires emerging from.