Add vector change detection foundation

docs/CODEX_EXECUTION_LOG.md

@@ -1,3 +1,22 @@
+## Sprint 18 vector change detection foundation (2026-06-16)
+
+Changed:
+- Added `POST /api/v1/analysis/change-detection` for comparing two vector datasets in the same project through the existing synchronous job envelope.
+- Added `ChangeDetectionService` with persisted `vector_features` as the primary source of comparable geometries and explicit stored-GeoJSON fallback warnings for older datasets.
+- Added frontend Change Detection controls, summary counts and MapLibre overlay styling for `added`, `removed` and `unchanged` feature properties.
+- Added backend tests for persisted-vector comparison and canonical API envelope behavior.
+
+Limitations:
+- The foundation classifies `added`, `removed` and `unchanged` only. It does not emit fake `changed` objects without durable object ids/versioning.
+- No migrations, live GRB/OSM/Sentinel fetching, AI inference, new dependencies, LiDAR, Copilot, Training Studio or separate Reports module were introduced.
+
+Validation:
+- `python -m compileall backend/app`
+- `cd backend && python -m pytest -W error::DeprecationWarning`
+- `cd frontend && npm run typecheck`
+- `cd frontend && npm run build`
+- `bash scripts/run_readiness_check.sh` via Git Bash on Windows
+- `cd backend && python -m alembic heads && python -m alembic upgrade head --sql`
 # Codex Execution Log
 
 This file must be updated by Codex after each implementation pass.