Is there a word to describe someone who is, or the state of being, content with hanging around others without interacting with them?

Solution 1:

The problem is that, much of the time, such behavior is seen as a sign of introversion, so the available expressions like wallflower denote shyness rather than something more productive like working contentedly in a busy coffee shop.

Meanwhile, a word like bystander emphasizes nonengagement, but in no way addresses the state of the person doing it. Are they content? Scared? Furthermore, a bystander suggests an activity or event: it doesn't make much sense to be a bystander in your own home when friends are over. As for its synonyms, onlooker and other options suggest a kind of observation that need not be present. You're not necessarily looking or listening all the time; you're playing video games or watching Netflix.

So because the direct options are imperfect, I suggest going more general and then specifying what you mean: you companion or accompany (verb) or you are companionate (adj). The verb usage of the word companion is fairly unusual, but it is attested in dictionaries like Merriam-Webster:

transitive verb

: accompany

He is companioned on the trip by his wife.

intransitive verb :

to keep company

fellows that he'd companioned with many years ago

Keeping company can entail a broad range of activity, from direct interaction to having people in the same space as you. Hence you are companionate: you suitably or harmoniously accompany others. You would need to specify how these terms should be understood through context, but in the context of your sentence with its gloss the phrasing would make sense:

She was truly companionate; always happy with people around but never feeling the need to join the conversation."

Or, with the verb and some modification:

She accompanies rather than participates; she is happy with people around but doesn't feel the need to join the conversation

Solution 2:

English has better options for describing the ongoing state of "comfort without interaction" than it does for describing a person who is habitually comfortable this way.

The phrases "companionable silence" and "comfortable silence" are commonly used to describe this state of affairs:

My husband and I can often be found together in companionable silence, whether out at dinner or at home, for which I am truly grateful.

(Joanna Rawbone, The joy of companionable silence)

If you can maintain a comfortable silence with someone and enjoy their company without fidgeting or worrying about what they are thinking, your relationship will stand the test of time.

(Arohie Chopra, How To Use Silence To Put Your Relationship To The Test)

These phrases contrast with "awkward silence."

However, I don't have a good term for a person who has the trait of finding such silences comfortable.

Informally, I would probably describe such a person as "chill," but this is much less specific than what you're asking for; it just means someone who is pleasantly non-stressful to be around. If I wanted to be more specific, I would have to bust out a whole sentence, like "Tom is usually pretty quiet, but he's good company."