[hua7450]

Summary

PolicyEngine/policyengine-core#600 adds TaxBenefitSystem.preprocess_situation, which SimulationBuilder.build_from_entities calls before building an entity-form situation. tests/core/_social_security_state_backend.py copies build_from_entities from the installed Core into a stand-in System that has no such method. CI installs the newest Core, so once Core releases the hook, test_social_security_input_state_machine.py would fail with an AttributeError on every PR, as it did after Core 3.33.13 (#10504) and 3.34.8 (#10684).

This PR gives the stand-in System a preprocess_situation that returns the situation unchanged. Today's Core never calls it, so the test behaves the same until the Core release, and the release doesn't break it.

The break comes from reading the backend and Core 600's builder change; the test was not run locally against Core 600.

Related

• PolicyEngine/policyengine-core#600: the Core hook.
• Build omitted household marital units from explicit couples and the tax-role fallback #10000: policyengine-us uses the hook to build omitted household marital units.

axiom: n/a: test fixture only, no change to a legal provision.

🤖 Generated with Claude Code

[PavelMakarchuk]

Verdict: APPROVE — the fix is correct, minimal, and safe to merge before PolicyEngine/policyengine-core#600 releases.

Suggestions

• The PR body can now state a tested result. The body says the break "comes from reading the backend and Core 600's builder change; the test was not run locally against Core 600". I ran it; see below.
• Comment wording (policyengine_us/tests/core/_social_security_state_backend.py:270-272). "policyengine-core PR 600" will age once the release has a version number. The nearby comment for _restore_count uses the form "From Core 3.33.13"; the same form here would match after the release. Optional.
• Longer term. This fixture has now needed a patch for three Core changes (3.33.13, 3.34.8, and this one), because it runs Core's method bodies on a stand-in system. A tolerant lookup in Core would avoid this case; I raised it as an optional point on PolicyEngine/policyengine-core#600. No change needed here.

What I verified

• The claim, reproduced. policyengine_us/tests/core/test_social_security_input_state_machine.py runs Core's build_from_dict -> build_from_entities source against the backend's stand-in System (lines 760-769 of the test; the backend copies the builder methods at _social_security_state_backend.py:662-675).

  Core installed	Backend file	Result
  3.34.10 (released, no hook)	main	1 passed
  3.34.10 (released, no hook)	this PR	1 passed
  PolicyEngine/policyengine-core#600 head f37aef590a	main	1 failed: AttributeError: 'System' object has no attribute 'preprocess_situation' at simulation_builder.py:229
  PolicyEngine/policyengine-core#600 head f37aef590a	this PR	1 passed

• CI exposure is real. The workflows run uv lock --upgrade-package policyengine-core (.github/workflows/pr.yaml:200, push.yaml:228, and others), so every PR would pick up the Core release.

• Signature. preprocess_situation(self, situation, default_period=None) matches Core's default and the call tax_benefit_system.preprocess_situation(input_dict, self.default_period). It returns the same dict, so the builder's type check passes. The fixture's situations always supply households, so an identity hook is the right behavior.

• No other stand-in is affected. I searched for every class that duck-types a system (MockSystem, FakeTaxBenefitSystem, _StubSystem, _RecordingSystem) and every caller of build_from_dict / build_from_entities. Only this backend passes a non-TaxBenefitSystem object to Core's entity builder. The other callers use the real CountryTaxBenefitSystem or a Core TaxBenefitSystem, which inherit the default hook. With the Core PR head installed, the 8 test files that hold those stand-ins and builder callers pass (362 passed).

• Repo rules. changelog.d/ss-backend-preprocess-situation-hook.fixed.md is a top-level fragment with a valid type. The body has axiom: n/a: test fixture only, no change to a legal provision.

• Diff scope. 2 files, +7/-0; no model code changes.

• CI at 1:57pm EST on Nov 12: 37 of 37 checks pass on head f1f04b5777.