chore(task): archive 08-18-native-traffic-signal-parity

.trellis/tasks/archive/2026-08/08-18-native-traffic-signal-parity/prd.md

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+# Native traffic signal parity with QGIS
+
+## Goal
+
+Move traffic-signal ownership from the QGIS editing chain into the native road
+compiler and Workbench. Existing QGIS signal assemblies remain import/export
+compatibility data during migration, but native overrides become the long-term
+source for generation, editing, and Blender/Cesium/preview delivery.
+
+## Confirmed Facts
+
+- QGIS currently edits `traffic_signal_assemblies.geojson`; this is the
+  migration input/output contract, not the desired long-term authority.
+- `scripts/reimport-gpkg.js` validates and reimports that legacy layer.
+- `scripts/build-area.js` currently derives runtime `traffic_signals.json` from
+  the edited assemblies; the native path must replace this dependency.
+- Existing native road layers do not read traffic-signal artifacts. Historical
+  native Cesium work intentionally omitted signal runtime assets.
+- Stable signal identity and editable fields already include `signal_uid`,
+  enabled state, source/control/approach IDs, arm direction, pose, mast reach,
+  and phase-group/runtime data.
+
+## Requirements
+
+- R1: Native compile/workbench must own a versioned area-local signal model and
+  override artifact, with an explicit one-time/import compatibility path from
+  existing QGIS assemblies.
+- R2: Workbench state must expose signal provenance and the existing editable
+  signal fields using stable IDs, and support generating, moving, rotating,
+  and deleting signal assemblies.
+- R3: Native compile and preview delivery must generate runtime signal data
+  directly from the native model, preserving enabled/disabled state, arm
+  direction/pose, and phase-group data without requiring QGIS.
+- R4: A compatibility adapter must import/export the existing QGIS assembly
+  format during migration and preserve legacy signal IDs where possible.
+
+## Scope Boundary
+
+- Native signal model and overrides are the long-term source of truth.
+- QGIS GeoJSON/GeoPackage support is transitional compatibility only; do not
+  make native compile depend on QGIS or regenerate native edits from QGIS.
+- Do not redesign signal geometry, timing logic, or vehicle behavior in this
+  task.
+
+## Acceptance Criteria
+
+- [ ] A native compile/reopen round trip preserves edited signal assemblies,
+  stable IDs, enabled state, and provenance without QGIS running.
+- [ ] The Road Workbench can generate, inspect, move, rotate, and delete signal
+  assemblies, then save durable edits without breaking QGIS reimport.
+- [ ] Native Blender/Cesium/preview consume runtime signal data generated from
+  the native model, including disabled signals being omitted from runtime.
+- [ ] QGIS import/export compatibility and legacy build stages continue to
+  pass while the migration adapter exists.
+- [ ] Nantaizi has documented native-only and QGIS-imported round trips.