Progressive concept teaching through three depth levels (Core → Mechanics → Deep Dive). Creates diagrams, provides annotated code walkthroughs from the current codebase, and builds explanations from fundamentals to production internals. Triggers: "teach me about [pattern/concept]", "how does [architecture/pattern] work", "walk me through [this implementation]", "tutorial on [concept]", "deep dive into [system/pattern]", "help me understand [this design]" Use when: user requests multi-level learning about code patterns, architecture, or implementation mechanics with checkpoint-based progression. Not for: quick answers, single-sentence explanations, code fixes, or "what does this line do" questions—those are standard assistance.