build-computed

name	build-computed
description	Build a feature's ecs computed-database — derived observable values.
input	feature
output	feature

Create ecs/computed-database/: computed-database.ts (extends the previous layer, adds computed from ./computed/index.js) plus a computed/ folder — one cached derived value per file + barrel. Derivation logic lives in data/; a computed only wires a db observable to it.

Comes after transaction-database.

The how is in the auto-loading features/ecs/computed.md rule.