A woman describes a lifelong pattern of assuming colleagues are undermining her, reading hostile intent into neutral comments, and gradually losing most of her friendships as a result, though she has never held a single fixed, specific belief that any one person is definitely plotting against her in a particular way. Before revealing the answer: is this best understood as a delusion of persecution?

No. This is better understood as paranoid personality disorder: a pervasive, longstanding pattern of suspiciousness across many relationships and contexts, without ever crystallising into a single fixed, specific delusional belief, which is what would be needed for a delusion of persecution. The progressive loss of friendships as a consequence of this suspicion, described here, is exactly the corrosive social pattern the phenomenon's own text describes — a personality-level trait rather than a discrete psychotic symptom.