A deep, opinionated, practical guide for the engineer who has just been handed (or is about to be handed) a team. The tactics, mental models, decision frameworks, and anti-patterns that take you from "great individual contributor" to "the person who makes the team 3x more effective." Grounded in 2026 reality — small teams, AI-leveraged engineers, async distributed work, and a hiring market that demands you ship. If you read only one section first, read §2 Mindset , §5 Technical Direction , and §9 The Operating Cadence . Everything else is the implementation of those three. Companion to saas_template_playbook.md (how to build), ai_saas_playbook.md (how to add AI), solo_founder_playbook.md (operating alone), and building_high_quality_ai_agents.md (agentic systems). This one is for the lead of a team of 3–10 engineers at a startup, a scale-up, or a fast pod inside a big company.…