Directory accounts an employee could be, for one system.

Read live from each provider rather than a mirror: unlike organizations, there is no table of Linear/Plain/Slack users — the ingest only ever stores the ones it already resolved, which is precisely not what a picker needs to offer.

Each source is isolated. Linear needs no new permission, Plain's users query needs user:read and Slack's needs the users:read bot scope, so one of the three may fail while the others work; that surfaces as a 502 for that source alone.

Disabled accounts are excluded unless asked for. They are still linkable — a departed person owns records and their account is the honest answer for that history — but they are noise in a picker whose usual job is naming a current employee.