SessionJob rows carry outputTotal exactly for record-declaring jobs, and a
new session.observeJob stream serves one job's retained record from an
absolute offset (anchor, coalesced output frames, terminal status) with the
fenced read resolved from the request's session — the same authorization
shape as the jobs roster. The client half gains ctx.jobOutput: the
reference-counted per-job observation service and its accumulated view
model, ported from the activity controller this replaces.