Целый, when used attributively, often has the implication of the speaker being annoyed or surprised: Он съел целую буханку хлеба = He ate a whole loaf of bread. Я ждал вас целый час. = I've been waiting for you for a good hour. Maybe весь vs целый is like the whole/entire vs a whole/an entire. When used predicatively, целый means intact/unharmed. Целый и невредимый = safe and sound
Given that ходить is multidirectional and пойти is unidirectional, I would assume that проходить is multidirectional and пройти is unidirectional. But that can't be true since those are different aspects of the same verb. So this is an exception to the rule that verbs come in unidirectional/multidirectional pairs. Why is this an exception? I.e., semantically, why does it make sense for this verb to be an exception?
That's what I'm asking.
The distinction multidirectional/unidirectional only applies to certain pairs of imperfective verbs without a prefix. There are about a dozen and a half such pairs, all referring to some kind of movement. Adding the same prefix to both verbs in such a pair turns them into a pair of verbs with a new meaning, where the verb derived from the mulidirectional one remains imperfective (although, sometimes, may have a perfective homomym) and the verb derived from the uniderectional member of the pair is perfective. More often than not such verbs have several meanings.
Take, for example, the pair ходить/идти. Both verbs are imperfective, the first being multidirectional, the second, unidirectional. When various prefixes are attached to идти, the root ид changes for ий or, in the case of притти, to ит (and the last и of the prefix blends with the first и of the root, so only one и remains). In the pair проходить/пройти the first verb, being imperfective, either refers to a repeated action or to the action in progress or, in the case of denial (не проходил), means 'have never'. Its perfective counterpart refers to either a one-time completed action or (in the negative form) a failure to perform one. Both verbs can have several meanings, including (1) pass by on foot, (2) cover (a certain distance in walking), (3) go/walk (through something), (4) pass/lapse (speaking of time), (5) subside (speaking of pain), (6) take place (speaking of events) (7) go (as in "How did it go?", (8) undergo (a certain procedure, (9) cover (certian topics in a course of training). In Addison, there are idioms such as "'этот номер не пройдет"= It's no go / The trick won't work / The cock won't fight. Maybe I've missed a few meanings.
Speaking of homonymy that I mentioned earlier, it can be seen on the example of заходить(imperf)/зайти (perf). Both verbs share the meanings "go in/ come in/drop by, walk behind, go (too far)" as a "imperfective/perfective" pair. But there is also a perfective verb заходить which means (1) start walking about (the room nervously), and (2) заходить ходуном = begin to shake (speaking of a house during the earthquake). Consider this passage: Ты давно ко мне не заходил. Но вот зашёл и началось землетрясение - весь дом заходил ходуном. (You haven't come to my place for a long time. But now that you did, an earthquake started and the house began to shake). :) This sort of homomymy is one of the most interesting facts about Russian language. I
Sorry, I'm not sure I understood you quite right. But if "multidirectional/unidirectional" means "несовершенный/совершенный вид", there is no exception, "проходить" and "пройти" are different verbs, "проходить" is несовершенного вида and "пройти" is совершенного вида. So, there is no exception, if I understood your question right. :)
Через has a broader scope of meanings than сквозь (or its non-standard alternative скрозь which you can hear in some dialects). Через may mean "across", "over", "through", "via", and, if used before words indicating the amount of time, "in" or "later". Сквозь only means "through" and can often, but not always, be replaced with через. Only сквозь can be used in the biblical idiom пройти сквозь игольное ушко (to pass through a needle eye) and in idioms "сквозь смех" and "сквозь слезы". Сквозь is more preferable in translating the phrases "through the hole" and "through the wall". Сквозь and через are interchangeable in "сквозь парк", "сквозь лес" and similar phrases where some kind of penetration or filtering is implied.