Polish export handoff artifacts

docs/CODEX_EXECUTION_LOG.md

@@ -3342,3 +3342,30 @@ Limitations:
 
 Next recommended pass:
 - After deploy and live validation, continue with export artifact action ergonomics or QA result drill-down, depending on the next live friction point.
+
+## Sprint 93 export handoff artifact polish (2026-06-21)
+
+Changed:
+- Added a `Latest handoff artifacts` section to `frontend/src/components/exports/ExportCenter.tsx`.
+- Grouped newest persisted artifacts for project report, project metadata, dataset GeoJSON, detection GeoJSON and segmentation GeoJSON.
+- Reused existing JSON preview and artifact download callbacks from latest artifact cards.
+- Added responsive latest artifact card styling in `frontend/src/styles/app.css`.
+- Added `backend/tests/test_sprint93_export_handoff_completion.py` to lock the grouped handoff surface, actions and responsive CSS.
+- Updated `CHANGELOG.md`, `docs/TODO.md` and `frontend/README.md`.
+
+Tested:
+- Red step: `python -m pytest backend\tests\test_sprint93_export_handoff_completion.py -q` failed on missing latest artifact grouping/actions/styles.
+- `python -m pytest backend\tests\test_sprint93_export_handoff_completion.py -q` (`3 passed`)
+- `python -m pytest backend\tests\test_sprint93_export_handoff_completion.py backend\tests\test_sprint64_export_handoff_polish.py backend\tests\test_sprint89_export_system_density.py backend\tests\test_sprint51_quality_export_polish.py backend\tests\test_sprint78_export_preview_readability.py -q` (`13 passed`)
+- `cd frontend && npm run typecheck`
+- `cd frontend && npm run build`
+- `bash scripts/run_readiness_check.sh` (`311 passed`; frontend typecheck/build passed; Alembic head `202606120900`; live smoke syntax passed)
+
+Open:
+- Tower deploy and live browser validation still pending for this pass.
+
+Limitations:
+- Export Center frontend handoff polish only; no API contract, persistence, migration, provider fetching or AI/model behavior changes.
+
+Next recommended pass:
+- After deploy and live validation, continue with QA/QC drilldown and map evidence layers.

docs/TODO.md

@@ -364,3 +364,4 @@ This file now starts with the current implementation status. Older preparation/b
 - [x] Add Overview workflow guidance for the V1 project -> data -> map -> QA/AI -> export path.
 - [x] Audit populated demo workflow and tighten complete-state Overview guidance copy.
 - [x] Make Overview workflow rail Map/Export clicks preserve useful dataset context.
+- [x] Add latest handoff artifact cards to the Export Center for report, metadata and GeoJSON outputs.