A flush ran its cascade under no id, so its executions and failures belonged
to no run. It now records a run with source "flush", and the holding run's id
travels on the queue item into a new `flow_run.parent` column, also on the
`/observability/runs` rows.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WgBfkm4rCmtd1T4vHWjEPx