Add deprecation alias for legacy labor_supply_responses paths

Mirror the two consumed paths (`income_elasticity` and
`substitution_elasticity`) under the renamed
`labour_supply_responses` tree back to
`gov.simulation.labor_supply_responses.*`, so the legacy
policyengine-app PolicyRightSidebar (which hard-codes the old
paths) keeps working between this PR landing and the matching app
PR rebuilding against the new path. Removes the merge-window
breakage that would otherwise hit the LSR sliders.

Remove this alias in a follow-up release once consumers (the app
PR PolicyEngine/policyengine-app#2829) have migrated.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: vahid-ahmadi

changelog.d/853.md

@@ -1 +1 @@
-- Rename `labor` to `labour` in LSR parameter and variable paths, labels, and descriptions to use British English spelling
+- Rename `labor` to `labour` in LSR parameter and variable paths, labels, and descriptions to use British English spelling. The two consumed paths (`gov.simulation.labor_supply_responses.income_elasticity` and `.substitution_elasticity`) remain available as deprecation aliases for one release so downstream consumers — particularly the legacy `policyengine-app` PolicyRightSidebar — keep working until they migrate.

policyengine_uk/parameters/gov/simulation/labour_supply_responses/aliases.py

@@ -0,0 +1,34 @@
+"""Deprecation aliases mirroring the renamed `labour_supply_responses` parameters
+under the legacy `labor_supply_responses` path.
+
+`policyengine-app` (legacy) hard-codes
+`gov.simulation.labor_supply_responses.{income_elasticity,substitution_elasticity}`
+in PolicyRightSidebar.jsx. Without this alias the LSR sliders break the
+moment a deployed app rebuilds against this version of policyengine-uk.
+The companion app PR (PolicyEngine/policyengine-app#2829) migrates to the
+new path; remove this alias once that ships.
+"""
+
+from policyengine_core.parameters import Parameter, ParameterNode
+
+
+_ALIASED_PARAMETERS = ("income_elasticity", "substitution_elasticity")
+
+
+def add_lsr_deprecation_aliases(parameters: ParameterNode) -> ParameterNode:
+    simulation = parameters.gov.simulation
+    canonical = simulation.labour_supply_responses
+
+    legacy_node = ParameterNode(
+        name="gov.simulation.labor_supply_responses",
+        data={},
+    )
+
+    for child_name in _ALIASED_PARAMETERS:
+        canonical_child: Parameter = getattr(canonical, child_name)
+        legacy_child = canonical_child.clone()
+        legacy_child.name = f"gov.simulation.labor_supply_responses.{child_name}"
+        legacy_node.add_child(child_name, legacy_child)
+
+    simulation.add_child("labor_supply_responses", legacy_node)
+    return parameters

policyengine_uk/tax_benefit_system.py

@@ -30,6 +30,9 @@
 from policyengine_uk.parameters.gov.economic_assumptions.lag_cpi import (
     add_lagged_cpi,
 )
+from policyengine_uk.parameters.gov.simulation.labour_supply_responses.aliases import (
+    add_lsr_deprecation_aliases,
+)
 from policyengine_uk.utils.parameters import (
     backdate_parameters,
     convert_to_fiscal_year_parameters,
@@ -93,6 +96,7 @@ def process_parameters(self) -> None:
         self.parameters = add_lagged_cpi(self.parameters)
         self.parameters = add_triple_lock(self.parameters)
         self.parameters = create_economic_assumption_indices(self.parameters)
+        self.parameters = add_lsr_deprecation_aliases(self.parameters)
 
         # Create baseline parameters for reform comparisons
         self.parameters.add_child("baseline", self.parameters.clone())