# Traffic Signals Split Matrix

Evidence gathered from `scripts/lib/traffic-signals.js` and repository-wide
call-site search on 2026-08-25.

| Export | Current users | Owner after P1 | Migration |
|---|---|---|---|
| `SIGNAL_LAYOUT` | `buildTrafficSignalsFromFeatures` | compiler package | Export from `@osm-asset/road-compiler/traffic-signals` |
| `signalNodeKey` | `buildTrafficSignalsFromFeatures` | compiler package | No host caller today; preserve public export for runtime identity contract |
| `buildTrafficSignalFeatures` | `native-traffic-signals`, `readTrafficSignalFeatures` | compiler package | Host QGIS adapter imports it from the package |
| `validateTrafficSignalFeatures` | `native-traffic-signals`, signal tests | compiler package | Tests import package entrypoint |
| `validateTrafficSignalSourceReferences` | `native-traffic-signals`, `reimport-gpkg`, `readTrafficSignals` | compiler package | Reimport adapter imports package function |
| `buildTrafficSignalsFromFeatures` | `native-traffic-signals`, `readTrafficSignals`, `buildTrafficSignals` | compiler package | Host preview adapter imports package function |
| `buildTrafficSignals` | `test-preview-assets` | compiler package | Test imports package function; it is geometry/schema behavior, not host I/O |
| `readTrafficSignalFeatures` | `build-osm2streets-qgis` | host adapter | Keep a thin file-reading wrapper under `scripts/lib/traffic-signals.js`; it imports package functions |
| `readTrafficSignals` | `build-area` | host adapter | Keep a thin file-reading wrapper under `scripts/lib/traffic-signals.js`; it imports package functions |

`scripts/lib/traffic-signals.js` must not retain a second implementation of
the schema or geometry. Its only P1 responsibility is host file I/O for the
legacy QGIS / preview paths. This preserves the one-way dependency:
host -> compiler package; the package never imports the host.