Harden Statbel population import compatibility

docs/CODEX_EXECUTION_LOG.md

@@ -1,3 +1,64 @@
+## Sprint 227 - Statbel population import compatibility preflight (2026-07-16)
+
+Implemented:
+- Added `scripts/statbel_population_preflight.py` as a local, fail-closed gate
+  between staged official Statbel archives and the existing population
+  provisioner. It performs exact source/edition allowlisting, bounded ZIP
+  inspection, population and geometry schema checks, EPSG:31370 and situation
+  date validation, geometry validity/area checks, sector joins, explicit
+  municipality reconciliation, national/scope total reconciliation and an
+  annualized baseline-change guard.
+- Removed the invalid historical assumption that `CD_SECTOR[:5]` always equals
+  the current `CD_REFNIS`. The 2025 REDEGEO layout can retain old sector codes
+  after a municipal merger; population and geometry must instead agree on
+  their explicit current municipality fields.
+- Kept official `ZZZZ` population rows in national and scope accounting while
+  excluding them honestly from map geometry. Bounded `make_valid` repair is
+  allowed only when the result remains polygonal, valid and area-preserving;
+  repaired sector codes are recorded in the manifest.
+- Hardened `provision_mol_population_history.py` so a new fetch is preflighted
+  before source retention or derivation, source ZIPs and the derived GeoJSON
+  are written atomically, and all three SHA-256 values are rechecked before
+  upload. Existing immutable Datasets remain idempotent; a legacy cached file
+  cannot create a new Dataset without `--force` restaging evidence.
+- Packaged the script in the all-in-one image, added it to readiness compile
+  checks and documented command, storage layout, evidence and limitations.
+  No API route, migration, scheduler, background fetch or existing Dataset was
+  changed.
+
+Validation:
+- Focused preflight/regional-time-series suite: 23 passed. It covers source and
+  member identity, missing schema, duplicate sectors, invalid totals, archive
+  traversal, CRS/date mismatch, explicit municipality mismatch, unexpected
+  non-spatial rows, bounded topology repair, excessive trend change, atomic
+  staging, source/snapshot tampering and legacy parser strictness.
+- Complete readiness passed with 815 backend tests, 110 documented routes,
+  one Alembic head `202607160001`, frontend typecheck and production build.
+  Static Alembic SQL, shell syntax, target Ruff and diff checks passed. A
+  repository-wide Ruff audit still reports 17 pre-existing warnings outside
+  this change; no unrelated refactor was performed.
+- Live compatibility-only execution inside the healthy Tower container used
+  locally staged official archives and made no API/database call:
+  - 2024 standard layout: 646 spatial Kempen sectors, spatial population
+    503,405, 28 `ZZZZ` rows / 276 unlocated inhabitants and accounted total
+    503,681 against the retained 2023 baseline.
+  - 2025 new REDEGEO layout: 733 spatial Kempen sectors, spatial population
+    506,473, 26 `ZZZZ` rows / 294 unlocated inhabitants and accounted total
+    506,767 against the retained 2024 baseline; annualized change 0.6094%.
+  - National 2025 accounting reconciled 21,183 population rows and 20,781
+    geometries to 11,825,551 inhabitants, including 402 `ZZZZ` rows / 7,654
+    unlocated inhabitants. Four official self-intersection cases were repaired
+    without area change and recorded by sector code.
+- The complete real 2025 operator staging path retained both source archives,
+  generated a 733-feature scoped GeoJSON and authorized source/snapshot hashes
+  in an isolated `/tmp/statbel-stage` directory. It did not import or replace a
+  Dataset.
+
+Boundary:
+- A passed preflight proves technical compatibility only. Adding a future
+  edition to `POPULATION_URLS` and replacing or importing any immutable Dataset
+  remains an explicit reviewed operator action.
+
 ## Sprint 226 - Governed Statbel population edition probe (2026-07-16)
 
 Implemented: