Adding an `S-N-A` / `S-N-H` Serial Prefix to Epic Sub-Issues to Split Work Between AI Agents and Humans

When we split an Epic issue into sub-issues, each serial number `S-N` represents one work unit. The AI-agent (Claude Code, Codex, and similar) share of that work becomes sub-issue `S-N-A`; the human share becomes `S-N-H`. When one work unit needs both, `S-N-A` and `S-N-H` sit side by side and each closes independently. When one side is enough, we only create that side. We used to draw the split too coarsely inside a single sub-issue: a checklist would mix tasks the agent could handle with tasks only a human could do (rotating production-equivalent credentials, coordinating with an external integration partner, making a UX judgment call). The agent would tick the boxes it could handle, file a PR, and the un-closable sub-issues piled up. Splitting at the sub-issue level while sharing the `S-N` serial keeps the ownership readable on the Epic view. This post covers the actual rules, how we pick the `-A` vs `-H` granularity, and how the prefix carries through to PR titles.