If you have 30 seconds. Holding an AI agent on the long run reveals something strange. The failures that cost you aren't the loud ones (a crash, a red build, a blank page), they're the ones that slip through the cracks of clean code. After 35 effective days, 109,000 lines and 517 commits on a solo ERP, I isolated five recurring silent modes, the fix that doesn't fix, the test that passes by construction, the memory that confabulates, the count that lies, the scope that creeps. One scene per mode, one rule per scene. A discipline doesn't get planned, it settles. The agent doesn't fail at random Late April 2026, I reread my accumulated feedbacks (close to a hundred files, dated, indexed) and found they were grouping around five families. The loud errors (red terminal, Sentry alert) you learn to recognize as you go. The silent ones cost more. The code passed, the agent announced green, production ran. And yet something had slipped. Five modes, five scenes, five rules. None of them was decided cold.…