Register tax_unit_role_input and filing_status_input as preserved engine inputs when moving past pe-us 2.2.1 #1027

Summary

PolicyEngine/policyengine-us#9617 adds two engine inputs whose names are the columns microunit already writes into every US build: tax_unit_role_input (person) and filing_status_input (tax unit). From the pe-us release that includes it, the role variables and filing_status read them. Today the loader drops both, and roles come from age ordering. The certified build populace-us-2024-spm-20260915 needs no rebuild, because the columns are already there.

When microcosm moves its engine pin past policyengine-us 2.2.1 to a release that includes PolicyEngine/policyengine-us#9617, three things follow.

1. The pinned input registry changes. POOL_ENGINE_INPUT_PROJECTION_CONTRACT (multispine_pool.py:343) pins engine_version="2.2.1", input_count=926, so the repin tool will see two more inputs.

2. The two inputs need registering as preserved engine inputs. Anything not registered falls through to:

   # packages/microcosm-build/src/microcosm/build/us_runtime/multispine_pool.py:1595-1598 (origin/main c8c0871cc)
           else:
               provision = "declared_absent_engine_input"
               available_by = "simulate"
               fallback = "policyengine_default_if_absent"

   The pe-us default for both is UNSPECIFIED, which falls back to age ordering. Registering them next to ("person", "is_related_to_head_or_spouse"): ("assembled", None) in _POOL_SIMULATION_PRESERVED_ENGINE_INPUTS (line 683) keeps the build-time simulation projection on microunit's roles, as the published model will use.

3. Nothing changes at export. Both are formula-free Enums whose member names are exactly microunit's strings (HEAD / SPOUSE / DEPENDENT; the five filing statuses), so the formula-owned and enum-domain gates pass as they do today.

Also relevant

• The recertification of policyengine.py bundle 6.1.1 against the same H5 bytes is described in Honor dataset-supplied tax-unit roles policyengine-us#9617's "Recertification" section.
• On the certified build, supplied roles move 2024 federal income tax by −$0.94B net and joint returns by −3.07M. Honor dataset-supplied tax-unit roles policyengine-us#9617 has the full before-and-after table.

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