#974 Condition operator: dependents run before the selected branch finishes; a one_success join of branch tails fails the run while the tail sleeps

EARS: When a Condition branch contains chained tasks, the Highway engine shall offer a way for a downstream task to run only after the selected branch's last task completes, and shall not fail the run while that task is sleeping. EVIDENCE (#961, API, tenant test): condition_with_parallel with verify_cond depending on branch_condition ran verify_cond at 00:38:28.845 BEFORE wait_true_parallel (00:38:29.065) and the parallel tasks, so p0..p2 were empty (run eb5034ce). With verify_cond dependencies [wait_true_parallel, false_task] trigger_rule one_success, the run FAILED: 'Task verify_cond has unsatisfied dependencies: [wait_true_parallel]' raised as ValueError while wait_true_parallel was in step_sleeping (run 99a99555). Reproduction: scripts/demo/demo_matrix/phase5_advanced.py condition_with_parallel.