Presume a member 20+ years younger is the claimant's child when no roles are supplied

changelog.d/2039-unflagged-gap.changed.md

@@ -0,0 +1 @@
+- Without any parent flag, a member at least 20 years younger than the claimant is now presumed to be their child at any age (`presumed_child.minimum_age_gap_at_any_age`), so ages 50 and 25 entered without relationships are a single claimant and an adult child, not a couple. Members 16 to 19 years younger stay partners from age 20. The presumption only applies where `is_claimant_or_partner` is not supplied: a dataset that carries it (such as policyengine-uk-data's enhanced FRS once it supplies the FRS roles) is unaffected, while datasets without it are not.

policyengine_uk/parameters/household/demographic/benefit_unit/presumed_child/age_limit.yaml

@@ -1,4 +1,4 @@
-description: Age below which a benefit-unit member much younger than the claimant is presumed to be the claimant's child rather than their partner, when relationships are not supplied. The limit does not apply when the claimant is flagged as a parent and no member under it, at least the minimum age gap younger, explains the flag. This is a PolicyEngine modelling presumption, not a statutory rule.
+description: Age below which a benefit-unit member much younger than the claimant is presumed to be the claimant's child rather than their partner, when relationships are not supplied. The limit does not apply when the claimant is flagged as a parent and no member under it, at least the minimum age gap younger, explains the flag, nor to a member younger by at least the minimum age gap at any age. This is a PolicyEngine modelling presumption, not a statutory rule.
 values:
   0001-01-01: 20
 metadata:

policyengine_uk/parameters/household/demographic/benefit_unit/presumed_child/minimum_age_gap.yaml

@@ -1,4 +1,4 @@
-description: Minimum age gap below the claimant at which a younger member is presumed to be the claimant's child rather than their partner, when relationships are not supplied. It applies at any age when the claimant is flagged as a parent and no younger member under the presumed child age limit explains the flag, and otherwise only under that limit. This is a PolicyEngine modelling presumption, not a statutory rule.
+description: Minimum age gap below the claimant at which a younger member is presumed to be the claimant's child rather than their partner, when relationships are not supplied. It applies at any age when the claimant is flagged as a parent and no younger member under the presumed child age limit explains the flag, and otherwise only under that limit; a larger gap (the minimum age gap at any age) applies at any age. This is a PolicyEngine modelling presumption, not a statutory rule.
 values:
   0001-01-01: 16
 metadata:

policyengine_uk/parameters/household/demographic/benefit_unit/presumed_child/minimum_age_gap_at_any_age.yaml

@@ -0,0 +1,6 @@
+description: Minimum age gap below the claimant at which a younger member is presumed to be the claimant's child rather than their partner at any age, even when the claimant is not flagged as a parent, when relationships are not supplied. A member flagged as a parent can still be the partner. This is a PolicyEngine modelling presumption, not a statutory rule.
+values:
+  0001-01-01: 20
+metadata:
+  unit: year
+  label: presumed child minimum age gap at any age

policyengine_uk/tests/policy/baseline/finance/benefit/family/housing_benefit/applicable_income/housing_benefit_applicable_income_disregard.yaml

@@ -460,8 +460,10 @@
     people:
       claimant:
         age: 70
+        is_claimant_or_partner: true
       partner:
         age: 50
+        is_claimant_or_partner: true
         employment_income: 3_000
     benunits:
       benunit:

policyengine_uk/tests/policy/baseline/gov/dwp/benefit_cap/benefit_cap_pension_age.yaml

@@ -21,8 +21,10 @@
     people:
       older:
         age: 70
+        is_claimant_or_partner: true
       younger:
         age: 50
+        is_claimant_or_partner: true
       child_1:
         age: 4
       child_2:
@@ -54,8 +56,10 @@
     people:
       older:
         age: 70
+        is_claimant_or_partner: true
       younger:
         age: 50
+        is_claimant_or_partner: true
         employment_income: 20_000
       child_1:
         age: 4
@@ -118,8 +122,10 @@
     people:
       older:
         age: 70
+        is_claimant_or_partner: true
       younger:
         age: 50
+        is_claimant_or_partner: true
         jsa_income_reported: 4_000
     benunits:
       benunit:

policyengine_uk/tests/policy/baseline/gov/dwp/lifetime_isa_capital.yaml

@@ -337,22 +337,27 @@
     pension_credit_assessable_capital: [4_000, 0]
 
 - name: Pension Credit counts a younger partner's Lifetime ISA after the charge
+  # The couple is 25 years apart, so the roles are supplied: without them the
+  # 45-year-old would be presumed the claimant's child.
   period: 2025
   absolute_error_margin: 0
   input:
     people:
       claimant:
         age: 70
+        is_claimant_or_partner: true
       partner:
         age: 45
         lifetime_isa_balance: 10_000
+        is_claimant_or_partner: true
     benunits:
       couple:
         members: [claimant, partner]
     households:
       household:
         members: [claimant, partner]
   output:
+    is_claimant_or_partner: [true, true]
     pension_credit_assessable_capital: 7_500
 
 - name: A dependent young person's Lifetime ISA does not count against the parent's claim

policyengine_uk/tests/policy/baseline/gov/dwp/pension_credit/is_pension_credit_eligible.yaml

@@ -160,17 +160,22 @@
     is_pension_credit_eligible: true
 
 - name: Case 4, mixed-age couple without protected exception is ineligible.
+  # The couple is 25 years apart, so the roles are supplied: without them the
+  # 54-year-old would be presumed the claimant's child.
   period: 2026
   input:
     people:
       person1:
         age: 79
+        is_claimant_or_partner: true
       person2:
         age: 54
+        is_claimant_or_partner: true
     benunits:
       benunit:
         members: [person1, person2]
   output:
+    is_claimant_or_partner: [true, true]
     is_pension_credit_eligible: false
 
 - name: Case 5, child in benefit unit does not block pension-age adult eligibility.

policyengine_uk/tests/policy/baseline/gov/local_authorities/council_tax_reduction/council_tax_reduction_pensioner.yaml

@@ -19,9 +19,11 @@
     people:
       older:
         age: 70
+        is_claimant_or_partner: true
         council_tax_benefit_reported: 700
       younger:
         age: 50
+        is_claimant_or_partner: true
     benunits:
       benunit:
         members: [older, younger]
@@ -130,8 +132,10 @@
     people:
       older:
         age: 70
+        is_claimant_or_partner: true
       younger:
         age: 50
+        is_claimant_or_partner: true
     benunits:
       benunit:
         members: [older, younger]
@@ -161,8 +165,10 @@
     people:
       older:
         age: 70
+        is_claimant_or_partner: true
       younger:
         age: 50
+        is_claimant_or_partner: true
       son:
         age: 30
         employment_income: 30_000
@@ -261,8 +267,10 @@
     people:
       older:
         age: 70
+        is_claimant_or_partner: true
       younger:
         age: 50
+        is_claimant_or_partner: true
     benunits:
       benunit:
         members: [older, younger]
@@ -285,8 +293,10 @@
     people:
       older:
         age: 70
+        is_claimant_or_partner: true
       younger:
         age: 50
+        is_claimant_or_partner: true
     benunits:
       benunit:
         members: [older, younger]
@@ -318,8 +328,10 @@
     people:
       older:
         age: 70
+        is_claimant_or_partner: true
       younger:
         age: 50
+        is_claimant_or_partner: true
       child:
         age: 9
     benunits: