juaristi22 · Sep 23, 2026 · Sep 22, 2026 · Sep 22, 2026 · Sep 22, 2026 · Sep 23, 2026
diff --git a/changelog.d/953-uk-local-authority-input.added.md b/changelog.d/953-uk-local-authority-input.added.md
@@ -0,0 +1 @@
+Supply the engine's household `local_authority` input from the rowwise geography ladder (#953): every assigned April 2023 ONS local authority code resolves to its policyengine-uk `LocalAuthority` member name through the sha-pinned ONS names-and-codes resource (`local_authority_names.json`, `tools/generate_uk_local_authority_names.py`) and the mechanical key rule with one declared alias; the assignment refuses any code the roster does not carry, the ladder gate reports any row whose input disagrees with its code, and the clone verifies the assigned members against the installed engine, so council tax and the bespoke Council Tax Reduction schemes stop seeing the Maidstone default on Microcosm builds. The input is declared on the export allow-list rather than the coverage manifest, which measures the incumbent surface; the engine pin moves to policyengine-uk 2.100.0, the first release whose `LocalAuthority` enum carries the six April 2023 unitaries, so the roster-wide membership check is green at the pin.
diff --git a/docs/shared-constants.md b/docs/shared-constants.md
@@ -51,3 +51,13 @@ from microcosm.calibrate.geography_constants import (
 Do not add another state FIPS/postal mapping to a country runtime or diagnostics
 module. Extend the shared definition and its consistency test when supported
 geographies change.
+
+The engine's `local_authority` member names are not a constants table: the 361
+April 2023 authority names are published ONS data, held in the sha-pinned
+resource `microcosm/build/uk/local_authority_names.json` (regenerate with
+`tools/generate_uk_local_authority_names.py`). Only the mechanical key rule and
+its declared aliases are code, in
+[`microcosm.build.uk_runtime.local_authority_input`](../packages/microcosm-build/src/microcosm/build/uk_runtime/local_authority_input.py);
+derive an engine key through `local_authority_engine_key` rather than
+re-implementing the rule, and resolve codes through
+`resolve_local_authority_engine_keys`, which fails closed (microcosm#953).
diff --git a/packages/microcosm-build/pyproject.toml b/packages/microcosm-build/pyproject.toml
@@ -39,7 +39,7 @@ us = [
 # The UK extra adds the rules engine for local metric generation from a
 # Microcosm UK H5. Target tables remain explicit inputs, and the base package
 # still does not import policyengine-uk at import time.
-uk = ["policyengine-uk>=2.98.0", "h5py>=3", "tables>=3", "openpyxl>=3.1"]
+uk = ["policyengine-uk>=2.100.0", "h5py>=3", "tables>=3", "openpyxl>=3.1"]
 
 [project.scripts]
 microcosm-export-us-l0-refit-h5 = "microcosm.build.us_runtime.l0_refit_export:main"

diff --git a/packages/microcosm-build/src/microcosm/build/uk/country_package.json b/packages/microcosm-build/src/microcosm/build/uk/country_package.json
@@ -307,6 +307,11 @@
       "kind": "legacy_json",
       "schema_id": "legacy_json"
     },
+    {
+      "path": "local_authority_names.json",
+      "kind": "legacy_json",
+      "schema_id": "legacy_json"
+    },
     {
       "path": "target_references.json",
       "kind": "legacy_json",

diff --git a/packages/microcosm-build/src/microcosm/build/uk/gates.json b/packages/microcosm-build/src/microcosm/build/uk/gates.json
@@ -625,6 +625,7 @@
           "household.household_is_cgt_band_donor",
           "household.household_is_spi_synthetic",
           "household.la_code_oa",
+          "household.local_authority",
           "household.lsoa_code",
           "household.mortgage_debt",
           "household.msoa_code",
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Supply the engine's household `local_authority` input from the rowwise geography ladder (#953): every assigned April 2023 ONS local authority code resolves to its policyengine-uk `LocalAuthority` member name through the sha-pinned ONS names-and-codes resource (`local_authority_names.json`, `tools/generate_uk_local_authority_names.py`) and the mechanical key rule with one declared alias; the assignment refuses any code the roster does not carry, the ladder gate reports any row whose input disagrees with its code, and the clone verifies the assigned members against the installed engine, so council tax and the bespoke Council Tax Reduction schemes stop seeing the Maidstone default on Microcosm builds. The input is declared on the export allow-list rather than the coverage manifest, which measures the incumbent surface; the engine pin moves to policyengine-uk 2.100.0, the first release whose `LocalAuthority` enum carries the six April 2023 unitaries, so the roster-wide membership check is green at the pin.