That loop is ~1,700 lines. The other 511,000 lines are the reasons it can run reliably for 50+ turns. Tool orchestration, permission management, context budgeting, analytics, error classification, session memory, model routing, config loading. The loop is where the agent runs. Everything else is where the agent survives. In most implementations, the loop stabilizes early. The harness - tool safety, context management, error recovery, permissions (all towards catching edge cases as they arise) - is where the engineering effort accumulates over time.