September 2026 Summaries

“Blast radius” is proposed as a way to measure the downstream work, cost, duration, reach, and rework generated by a single engineering decision, linking RFCs, code history, and AI-agent session records. Using a decision to restructure software components into standalone “cassettes” as a case study, the authors traced 474 sessions over 27 days across three engineers and eight repositories, finding that a $57.05 design session led to at least $4,704.74 in subsequent work, a 65-fold amplification. Although implementation accounted for most human sessions, deployment and migration represented 87% of spending, including one $2,633.11 deployment session, while ongoing automated evaluations added a continuing measurement cost. The analysis also identified costly rework, such as a discarded alias subsystem, a replaced manifest format, and a production database-query fix during migration, illustrating that decision consequences can persist after a project appears complete. The method relies on grouping session records through shared identifiers and prompt evidence, while acknowledging it produces a conservative estimate because unlabelled related work may be missed; the authors argue that as AI lowers execution costs, organizations should place greater scrutiny on the upstream decisions that direct that work.