I wanted C4 diagrams in Markdown, in my editor, offline. The tools I found didn't do that, so, in the familiar spirit of another weekend project, I built it with an agent. C4X now ships on the VS Code Marketplace and Open VSX and inside Google's Antigravity IDE. Across it and my other extensions, the recorded tally exceeded 12,000 installs on 30 September 2026.

The build was quick. Maintaining what I shipped became the continuing work.

This is the story of what sits around the agent that built it: context with one authoritative home, skills for the work I repeat, deterministic gates, a release that tests the package the user installs, and the harness that became a plugin I now use to start every project. I'll walk one real change through it, share the field notes the install count doesn't tell you, and be honest about the work needed to keep shipping.

Takeaways:
1. Shipping with an agent is fast; maintaining what you shipped is the real work. Plan for it from the first weekend.
2. Give every decision one authoritative home, write skills for the work you repeat, and keep the gate deterministic.
3. An install count measures distribution. Separate it from adoption, and read the rejection before you count the activity.

30 minutes (25 + 5 Q&A). Intermediate. For builders, GDG/DevFest and AI-engineering meetups. A prepared case-study session; final screenshots and rehearsal are in progress. Install totals are a dated distribution measure, not a count of active users.