Capture values events as a drainable stream of state snapshots.
Keeps _latest / _interrupted / _interrupts as scalar state
regardless of whether the log has a subscriber ā so run.output()
and run.interrupted work without forcing the caller to iterate
run.values. Log pushes are silent no-ops when unsubscribed.
Native transformer ā projection keys are exposed as direct
attributes on the run stream (e.g. run.values).
Only values events at the run's own level are captured; snapshots
from deeper subgraphs are left in the main event log but excluded
from the projection. "Own level" is defined by scope, which
stream_v2 / astream_v2 populate from the caller's checkpoint
namespace so that a nested stream_v2 call still sees its own
root snapshots.
The error that ended the run, or None if it succeeded.
Set by the mux when it auto-fails the projection log.
