Багетная мастерская открыта.

Because открыта is the short form of the adjective открытый and is commonly used in Russian to mean is open in a predicate:

• Мастерская открыта. = The workshop is open.

The long form открытая usually describes a noun directly:

• открытая мастерская = an open workshop

So in this sentence, открыта means the state of the workshop, not just a permanent descriptive quality.

It agrees with мастерская, which is feminine singular.

Short-form adjectives change by gender and number:

• masculine: открыт
• feminine: открыта
• neuter: открыто
• plural: открыты

Since мастерская is feminine, you get открыта.

Yes—if you think in English terms, there is an implied is.

Russian normally omits to be in the present tense:

• Багетная мастерская открыта. = The baguette/framing workshop is open.

There is no present-tense word like is in ordinary Russian sentences of this type.

Because it agrees with мастерская.

Both words are nominative singular feminine:

• багетная = adjective, feminine singular
• мастерская = noun, feminine singular

Russian adjectives must match the noun they describe in gender, number, and case.

They are in the nominative case.

This is the normal case for the subject of the sentence:

• Багетная мастерская = the subject
• открыта = what is being said about it

So the structure is basically:

• [subject in nominative] + [short-form adjective]

Here мастерская is a noun meaning workshop, studio, or shop depending on context.

It is feminine, which is why related words agree with it in feminine form.

A learner may notice that some Russian nouns look like adjectives, but мастерская is a normal noun here.

It is an adjective formed from багет.

Depending on context, багет in Russian can refer to:

• a baguette in the bread sense
• more often in business/shop language, frame moulding for pictures and mirrors

So багетная мастерская often means something like a framing workshop rather than a bakery. The exact meaning depends on the context already given to the learner.

Yes. Russian word order is fairly flexible.

The neutral order here is:

• Багетная мастерская открыта.

But other orders are possible for emphasis, for example:

• Мастерская открыта.
• Открыта багетная мастерская.

The original version sounds natural and straightforward, especially as a simple statement or sign.

Yes, very normal.

Russian commonly uses a short-form adjective for this:

• Магазин открыт. = The shop is open.
• Аптека открыта. = The pharmacy is open.
• Мастерская открыта. = The workshop is open.

So Багетная мастерская открыта follows a very common pattern.

A natural stress pattern is:

• баге́тная мастерска́я откры́та

A rough pronunciation guide:

• ба-ГЕТ-на-я
• мас-тер-СКА-я
• от-кры-ТА

One important point: unstressed vowels are reduced in Russian, so the written vowels do not always sound as clear as they look.

Russian does not have articles.

So Багетная мастерская открыта could mean:

• The baguette/framing workshop is open
• A baguette/framing workshop is open

The exact choice in English depends on context.

Yes, in other contexts открытый / открыта can also mean open in a broader sense, such as:

• physically open
• open-minded
• public / not closed
• accessible

But in a sentence about a shop or workshop, открыта almost always means open for business or currently open.