Pali loves using close synonyms. English loves clear distinctions. And so we try to understand each other. The PTSD (Pali Text Society Dictionary) entries show something of the challenge:
Sampajañña
neuter
attention, consideration, discrimination, comprehension, circumspection AN.i.13 sq.; AN.ii.93; AN.iii.307; AN.iv.320; AN.v.98 sq. SN.iii.169; DN.iii.213 (sati + samp . opp. to muṭṭha-sacca asampajañña ), DN.iii.273. Description of it in detail at DN-a.i.183 sq. = Vb-a.347 sq., where given as fourfold , viz sātthaka˚, sappāya˚, gocara˚, asammoha˚, with examples Often combined with sati , with which almost synonymous,* e.g. at DN.i.63; AN.i.43; AN.ii.44 sq.; AN.v.115
&
Sati
feminine
memory, recognition, consciousness, DN.i.180; DN.ii.292; Mil.77–Mil.80 intentness of mind, wakefulness of mind, mindfulness alertness, lucidity of mind, self-possession, conscience self-consciousness DN.i.19; DN.iii.31, DN.iii.49, DN.iii.213, DN.iii.230, DN.iii.270 sq. AN.i.95; Dhs.14; Mnd.7; Tikp.61; Vb-a.91; Dhs-a.121; Mil.37;
Maybe we should accept that the two words are * "almost synonymous" and not attempt too strenuously to over-define them.
(OPINION only.)