Qualify targeted childcare through Pension Credit only on receipt of a guarantee credit

[MaxGhenis]

Fixes #1956

Summary

Targeted (2-year-old) childcare listed the guarantee_credit amount as a qualifying benefit. This PR lists in_receipt_of_guarantee_credit instead, so the Pension Credit route needs a claim and a payment, as SI 2014/2147 reg 1(2) "eligible child" (a)(ii) needs entitlement.

Main has moved since #1956 was filed. #1896 (merged 2026-10-02) gave guarantee_credit defined_for = is_pension_credit_eligible, so working-age families no longer get a computed guarantee credit. That was the half of #1956 that moved money. What this PR still fixes: a Pension Credit eligible pensioner who does not claim Pension Credit qualifies through the computed amount on main.

in_receipt_of_guarantee_credit (on main from #1909, also read by the pensioner CTR rules) now also requires pension_credit > 0, with or without the Pension Credit freeze. A reform that stops Pension Credit being paid (for example by neutralising pension_credit) left receipt true. In the unreformed model this changes nothing (see impact).

The law

• SI 2014/2147 reg 1(2), "eligible child" (text valid from 1 January 2026): a young child "whose parent is entitled to any one or more of the following— ... the guaranteed element of state pension credit under the State Pension Credit Act 2002;" (item (ii)).
• SPCA 2002 s.1(2): "A claimant is entitled to state pension credit if— (a) he is in Great Britain; (b) he has attained the qualifying age; and (c) he satisfies— (i) the condition in section 2(1) (guarantee credit); ...". s.4(1A): "A claimant is not entitled to state pension credit if he is a member of a couple the other member of which has not attained the qualifying age" (from 15 May 2019, subject to the SI 2019/37 art 4 saving).
• SSAA 1992 s.1(1): no person "shall be entitled to any benefit unless ... he makes a claim for it ... or ... he is treated ... as making a claim for it"; s.1(4)(ab) covers state pension credit, and SPCA s.17(1) construes "entitled" through it.

Household example (2026, North East)

Parent aged 68 with a State Pension of £10,000 and a 2-year-old, not claiming Universal Credit:

	main (2efc8d8)	this PR
Minimum guarantee (£12,376 + £3,638.96)	£16,014.96	£16,014.96
Computed guarantee_credit	£6,014.96	£6,014.96
Not claiming PC: pension_credit	£0	£0
Not claiming PC: eligible / entitlement (child)	true / £5,002.07	false / £0
Not claiming PC: household_net_income	£16,428.62	£11,426.55
Claiming PC: eligible / entitlement (child)	true / £5,002.07	true / £5,002.07

Enhanced FRS impact

Real runs of origin/main 2efc8d8 and this branch at ad8e55d on enhanced_frs_2024_25.h5 (sha256 e433e532…), one microsimulation per package covering 2025–2030. Weighted totals, float64 sums, exact array comparisons.

• Targeted childcare spending, children receiving it, household net income, HBAI income, household benefits, gov spending and balance, council tax reduction, and BHC/AHC poverty are identical in every year 2025–2030. No benefit unit loses or gains an entitlement amount.
• Every other saved benefit-unit array is identical, including in_receipt_of_guarantee_credit, Pension Credit and Housing Benefit, so the payment condition changes nothing in the baseline.
• targeted_childcare_entitlement_eligible turns false for 68–90 records (23.1k–29.0k weighted benefit units a year: 26.2k in 2025, 29.0k in 2026, 23.1k in 2030). All are Pension Credit eligible pensioners in England who do not claim Pension Credit, with a computed guarantee credit and no 2-year-old, so no entitlement is paid either way.
• On Qualify targeted childcare through Pension Credit only on receipt of a guarantee credit #1987's earlier base (da947ee, before Replace generic child and adult flags with each programme's legal definitions #1896) the same route cost £39–42m a year; Replace generic child and adult flags with each programme's legal definitions #1896 removed that.

Scripts and outputs, kept in the author's evidence folder and not in the repo: impact/tce_impact.py (the runs), impact/tce_compare.py → impact/compare.json, impact/eligibility_flag_changes.py → impact/eligibility_flag_changes.txt (the lost-flag breakdown, built from the saved arrays; the script was saved after the first run and re-run with identical output), and out/household.py → out/household_main.json, out/household_branch.json (the household example).

Invariants (Hypothesis, test_targeted_childcare_guarantee_credit_properties.py)

Populations mix working-age, pension-age and mixed-age families with a 2-year-old, some with a dependent young person aged 16–19, across the four nations, in 2025, 2026 and 2029.

1. Qualifying age: no benefit unit whose adults are all below the qualifying age qualifies through the Guarantee Credit route. Fails for the route as filed; holds on main since Replace generic child and adult flags with each programme's legal definitions #1896 and here.
2. Route identity: eligibility = claims, England, not extended-entitlement eligible, and one route open.
3. Receipt (unreformed): route open exactly when pension_credit and guarantee_credit are both positive; implies a claim and, for the generated families (none reports Pension Credit or pension-age Housing Benefit, so none has the SI 2019/37 saving), that the claimant and any partner are over State Pension age. A dependant aged 18 does not block it (one known family, and YAML Cases 12–13).
4. Differential vs main: never adds eligibility; removes it exactly for eligible non-claimants with no other route.
5. Not claiming Pension Credit closes the route and never makes a family eligible. Fails for the filed route and for main; holds here.
6. Not claiming targeted childcare never leaves a family eligible.
7. A reform that stops Pension Credit payments closes the route, with or without the freeze (fixed examples, not generated).
8. Under the Pension Credit freeze the route follows the baseline receipt (fixed example, not generated).

A mutation test runs the filed and main routes through the same eligibility formula and checks that each breaks the invariant it was written against.

Tests

• targeted_childcare_entitlement_guarantee_credit.yaml: 14 cases. Case 9 is a mixed-age couple without the SI 2019/37 art 4 saving (does not qualify); Case 14 is the same couple with the saving (qualifies: couple minimum guarantee £18,889 + £3,638.96 − State Pension £10,000 = £12,527.96 paid).
• Adds in_receipt_of_guarantee_credit.yaml (not on main): Key the Housing Benefit Guarantee Credit passport on receipt #1927's six cases. Case 3's name and comment now describe main's inferred saving (Date the mixed-age couple Pension Credit exclusion and model the SI 2019/37 saving #1940), so the file is no longer byte-identical to Key the Housing Benefit Guarantee Credit passport on receipt #1927's; whichever merges second keeps this wording.
• Local at ad8e55d: full YAML suite 2,109 passed; the property file 7 passed (234 s).
• Mutants of in_receipt_of_guarantee_credit and the parameter: reverting the parameter entry, dropping the payment term, and making the freeze branch use the current formula each fail a test. Dropping would_claim_pc or is_pension_credit_eligible fails none: under the model's formulas a payment already implies both (pension_credit = entitlement × claim; entitlement and guarantee_credit are defined only for eligible units). They differ only when pension_credit or guarantee_credit is supplied as an input, so the terms stay as a guard.

Known departures (unchanged by this PR)

• The SI 2019/37 art 4 saving is inferred from reported Pension Credit or pension-age Housing Benefit (has_mixed_age_couple_pension_credit_saving, from Date the mixed-age couple Pension Credit exclusion and model the SI 2019/37 saving #1940) unless set directly. A saved couple qualifies (Case 14).
• The model does not distinguish entitlement from payment. In law they can differ, for example where SI 2002/1792 reg 13 makes a credit under 10p a week unpayable.
• The model tests the benefit unit's claimant and partner, not "the child's parent".
• would_claim_pc is the claim (a take-up draw in the Enhanced FRS).
• Annual eligibility does not apply the statutory guidance A1.4 continuation, so a reform that closes a route overstates first-year losses for children already in a place.

Overlaps

• Count only the claimant's and partner's legacy awards in means tests and passports #2027 edits the same parameter file (renames the JSA/ESA entries); whichever merges second keeps both changes.
• Date the mixed-age couple Pension Credit exclusion and model the SI 2019/37 saving #1940 (merged) edited the same sentence of the in_receipt_of_guarantee_credit docstring. The merge in 95aed89 keeps this PR's payment check and takes Date the mixed-age couple Pension Credit exclusion and model the SI 2019/37 saving #1940's account of the saving.
• Key the Housing Benefit Guarantee Credit passport on receipt #1927 adds in_receipt_of_guarantee_credit.yaml too (see Tests); it already conflicts with main elsewhere.

Review

An independent reviewer approved head 314f457, and a second pass approved the follow-up commit c47e283 (the freeze-path payment check). A merge-only delta review of ad8e55d (the two merges of main) is pending. Their should-fix and nit findings are addressed above or listed under known departures; a follow-up for the same payment check on in_receipt_of_savings_credit_only is tracked separately.

Axiom

axiom: TheAxiomFoundation/rulespec-uk#400 queued (extension comment for reg 1(2) "eligible child" (a)(ii): law, required outputs, review_finding and companion cases G1–G6; SI 2014/2147 reg 1 is not yet in the corpus, so the signed encode waits on ingestion)

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