#783 HIGH: complete_run locks run but not task table - state inconsistency risk

complete_run locks run row with FOR UPDATE but updates task table without locking. Another process could claim different run for same task, causing task state 'running' overwritten to 'completed'. Location: migrations/01KCFHD0PAR43NCPHN7J0VVT2K:185-240. Fix: Add FOR UPDATE on task row before update.