Document the work-program participation inputs as unsourced assumptions

[daphnehanse11]

Closes #249; advances #248. Stacked on #352 (draft until it merges, then rebases to main — the diff vs #352 is one register extension plus contract tests).

Summary

The CPS ASEC has no item measuring SNAP E&T, qualifying work-program, or workfare participation — confirmed against both the raw ASEC column inventory and the retired enhanced-CPS pipeline, which never carried these inputs either. Per #249's scope ("if no source exists, add an explicit release diagnostic/documented assumption rather than relying on an invisible default"), this adds the three work-program inputs to the documented_absent_inputs register introduced in #352:

• is_snap_work_program_participant — general work-registration compliance via program participation never fires; USDA reports E&T reaches a small minority of participants, so the always-False default understates compliance only modestly.
• weekly_snap_work_program_hours — combined work-plus-program hours toward the 20-hour ABAWD test omit program hours.
• is_snap_workfare_participant — workfare under 7 CFR 273.7(m) satisfies the ABAWD requirement regardless of hours; defaults False.

Contract tests

New test_us_documented_absent_inputs.py pins the register: exact coverage of the six known unsourced inputs, every entry citing a tracking issue, disjointness from the degenerate-exclusions register (persisted-stuck vs never-persisted classes must not overlap), and no seeded input (pregnancy, disability, discretionary exemptions) listed as absent.

Why documentation rather than seeding

Unlike pregnancy (#352) or discretionary exemptions (#353), there is no statutory rate or stable administrative share to seed against at the person level — E&T participation is state-program-specific and small. If a citable assignment basis emerges (e.g., state E&T participation counts), the register entry converts to a seeded stage the same way; until then the honest treatment is a visible always-False assumption.

🤖 Generated with Claude Code

[daphnehanse11]

#352 merged, so this is rebased onto main and out of draft — the diff is now exactly the register extension (three work-program entries) plus the contract tests.