The profession window answered from a copy a feed refreshed once a frame, and rebuilt and signalled there, so a getter or TRADE_SKILL_UPDATE between two packets read the frame's last state.
**Reference**
- An item answer runs the getter's or the build's record callback (`0x4fdc30`, `0x4fc8e0`), which rebuilds and signals at its packet.
- The build reads the book at its call (`0x4fca20`), and with no player it empties the list and signals nothing (`0x4fca52`, `0x4fcb1b` → `0x4fd170`).
- GetTradeSkillLine reads the open line at the call (`0x4fdd40`).
**Changed**
- The callbacks go on the item cache's list.
- The build and the getters read through the host.
- A build with no player empties the book silently.
- `feed_trade_skill` is gone.
**Tests:** the line getter between two packets, a reagent's answer between two falls, a learn banded at its packet, a product answer after `/reload`, and the silent empty build.
Part of #2168 and #2217.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Sam Sung
4b6ef4b2c6