Runtime dependency resolution for workflow jobs.

Called at the start of each perform/1. Loads the current job's node to get its dependencies and flags, then resolves the state of each dependency by joining workflow_nodes to oban_jobs.

States and outcomes

A dep whose Oban job was pruned comes back from the LEFT JOIN with a nil state and is treated as pruned. A dep stuck in executing past the stale threshold is treated as failed rather than snoozing forever.

Ordering edges are not dependencies

A node's sequence_after is resolved separately and by a weaker rule: it snoozes while the predecessor is pending and proceeds on every terminal state, failures included. It is how the sequential fan-out gate paces an expansion, and no data flows along it — the successor reads nothing the predecessor produced, so a predecessor that dies has nothing to invalidate.

Treating it as a dep is what let one exhausted fan-out branch kill a whole run. The branch was discarded; its successor read a failed dependency and cancelled; the next successor cancelled on that; and the cascade arrived at the reader configured to tolerate precisely this case (ignore_discarded: true) as a wall of cancelled deps, which that flag does not cover. Every completed step in the run was discarded with it.