Revisamos a pauta até a assembleia de condomínio começar.

Portuguese often leaves out subject pronouns when the verb already shows who the subject is.
Here, revisamos tells you the subject is we.

So:

• Revisamos a pauta... = natural
• Nós revisamos a pauta... = also correct, but more explicit or emphatic

A speaker might add nós for contrast, emphasis, or clarity, but it is not necessary.

It can mean either one.

For many -ar verbs in Portuguese, the 1st person plural form is the same in the present and the preterite:

• revisamos = we review
• revisamos = we reviewed

Context tells you which one is meant. In an isolated sentence like this, many learners first read it as past, but it could also be present depending on the situation.

For example:

• Sempre revisamos a pauta até a assembleia começar. = clearly a routine, so present
• In a narrative about yesterday, revisamos would be understood as past

Portuguese uses definite articles more often than English does.

Here, both nouns refer to specific things that the speakers already know about:

• a pauta = the agenda / the list of items being discussed
• a assembleia de condomínio = the condo meeting / homeowners’ association meeting in question

In English, you might sometimes omit the in similar situations, but in Portuguese the articles sound very natural and expected here.

In this kind of context, pauta is especially natural for a meeting. It usually means the agenda, discussion topics, or items to be covered.

Agenda exists in Portuguese too, but in Brazilian Portuguese it often also means:

• a planner
• a schedule
• a calendar
• someone’s timetable

So in a formal meeting context, pauta is often the better choice if you mean the list of matters to discuss.

Até means until / up to the point when.

It marks the endpoint of the action:

• Revisamos a pauta até a assembleia de condomínio começar.
• We reviewed the agenda until the condo meeting started.

In some English contexts, a translation with before may sound natural, but grammatically até is really expressing an endpoint, not just simple earlier time.

If you specifically wanted before, Portuguese would normally use antes de.

Because after até, Portuguese often uses an infinitive clause instead of a fully conjugated verb.

Here, começar is functioning as an infinitive after até:

• até ... começar

More specifically, this is the personal infinitive, because the infinitive has its own subject: a assembleia de condomínio.

In the 3rd person singular, the personal infinitive looks exactly the same as the regular infinitive:

• começar

That is why you do not see começa or começou here.

A useful comparison:

• até a assembleia começar = until the meeting starts/started
• até os convidados chegarem = until the guests arrive/arrived

Notice how in the plural you can clearly see the personal infinitive ending: chegarem.

Because começar can work in two different ways:

1. começar by itself = to begin / to start

   • A reunião começou. = The meeting started.

2. começar a + infinitive = to begin to do something

   • Começamos a discutir. = We began to discuss.

In your sentence, a assembleia de condomínio is the thing that begins, so começar is being used by itself:

• a assembleia ... começar

There is no second verb after começar, so there is no reason to use começar a.

Both can be possible, but they are not exactly the same in nuance.

• assembleia de condomínio often sounds like the name of the type of meeting: a condo association meeting
• assembleia do condomínio points more directly to the meeting of the specific condo/building

So de condomínio is often a more general label, while do condomínio can feel more tied to one particular condominium.

In real life, native speakers may use both, but assembleia de condomínio is a very common fixed expression in Brazilian Portuguese.

You could, but the meaning may become less clear.

Até a assembleia de condomínio começar clearly shows that the meeting is the subject of começar.

If you say até começar a assembleia de condomínio, it can sound more like until someone starts the condo meeting, where a assembleia is interpreted as the object of começar.

So the original wording is clearer if you want the meaning until the condo meeting started/began.

Yes.

In até a assembleia de condomínio começar, the noun phrase a assembleia de condomínio is the subject of começar.

A very literal structural reading is:

• until [the condominium meeting] begin

Of course, in natural English you would say until the condominium meeting began / starts, but in Portuguese it is normal for the subject to appear before the infinitive like this.