The session_projection_parity module pinned fabro's stage fold to pebble's
SessionProjection while both existed; the stage view reads the fold now,
and the one usage rule has its own tests. StageProjection.agent_control
and AgentControlState go too: pebble's fold carries the interrupted and
steered facts as agent.activity, and the stage's state says whether the
stage still runs, which is what the reset on fabro's own stage events was
for. The run-detail banner reads activity plus state.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>