Adjective for "terrified yet calm and capable"

The following don't explicitly satisfy the terrified criteria; they are instead words that represent calmness under pressure. Terror could be construed to be a form of pressure.

Equanimity is defined as:

evenness of mind especially under stress

Its adjective would be equanimous.

Its synonym, sangfroid, is defined as:

self-possession or imperturbability especially under strain

While the dictionary does not note its adjectival properties, you can probably use it as one. A sangfroid calm is a reasonably common phrase.

Unflappable is similarly defined:

having or showing calmness in a crisis

They can be described as mechanical, stoic, businesslike, calm under pressure, or having icewater in their veins.

In French, this term is "sang-froid".

The adjectives calm, composed and equanimous already have the connotation of one being possibly in a terrible situation.

I like stoic for the given situation:

A person who can endure pain or hardship without showing their feelings or complaining.

I like resolute. Definition from Google:

Admirably purposeful, determined, and unwavering