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--- name: til description: Teach the user exactly ONE thing from the current session or project, in plain English, one or two short paragraphs. Use when the user types ;til or "til", asks "what did I learn", "explain one thing from this session", or at session close alongside other closing rituals. Also appropriate mid-session when a concept keeps recurring that the user clearly hasn't used themselves. One thing only — never a list, never a lecture. version: 1.0.0 --- # til The user is a builder who ships real things, often without a formal CS background. Terms fly past in every session; they usually search them alone afterward. This skill closes that gap: one concept per run, taught properly, from THIS session — not generic trivia. ## Picking the one thing Priority order — take the first that applies: 1. A term or concept that appeared 2+ times in the session that the user never used in their own words (they worked around it). 2. The concept behind a mistake that was made and fixed — teach the why, not the blame. 3. A tool, pattern, or piece of syntax that was used silently and did real work (e.g. a flag, an atomic write, a data structure choice). 4. Fallback only: a genuinely good fun fact connected to the session's language, tool, or history. One thing. If two are tempting, save the second for the next run — say "there's another one banked for next time" and nothing more. ## How to teach it - Name the term first, exactly as it's written, so it can be searched. - One or two short paragraphs. Plain English. Every jargon word used in the explanation must itself be explained or dropped. - Analogies are welcome — physical-world analogies (music production, signal flow, cooking, workshops) land better than CS metaphors. - End with one line: why it mattered in THIS session specifically. - Close with: "Want the deeper version?" — and only expand if asked. The deep version may go longer, show code, and link docs. ## Output footer Last line, always, greppable: ``` TIL: <term> — <summary in ten words or fewer> ``` ## Hard rules - Exactly one concept. Never a list. Never "3 things you learned." - Default length: two paragraphs max. Expansion only on request. - Must come from the actual session content. If the session was trivial, say so and use priority 4 — never invent relevance. - Never condescend. The user ships production apps; missing vocabulary is not missing ability. - Don't repeat a TIL already given in the same project — check earlier TIL: footers if visible.