Threadline.NotFoundError is raised by the ! sibling of a single-subject lookup when the subject does not exist or is not visible under the caller's scope.

The message carries only the id the caller passed in — never row data, scope terms, or wording that distinguishes an existing-but-scope-filtered row from a genuinely missing one. resource names the subject looked up: :audit_transaction for Threadline.audit_transaction!/2 and the other single-subject transaction lookups' ! siblings.

Implements Plug.Exception (status/1 returns 404, actions/1 returns []). Unlike Ecto.NoResultsError, which gets its 404 mapping from phoenix_ecto, Threadline depends on :plug directly (mix.exs), so it owns its own status.