Add dimension guards for ORG hourly_wage imputation

[hua7450]

Summary

• Adds dimension validation at every stage of the ORG imputation pipeline to prevent hourly_wage (and other ORG variables) from being stored with the wrong number of entries
• Fixes CPS.downsample() to drop variables unknown to the current policyengine-us instead of silently keeping stale (un-downsampled) arrays

Closes #675

Context

enhanced_cps_2024.h5 on HuggingFace has hourly_wage with 284,250 entries (the raw ORG donor row count) instead of matching the person count in the simulation. This causes a ValueError in Microsimulation() that blocks CI for all open PRs on policyengine-us.

Changes

Dimension guards (4 files)

Location	Guard
org.py: predict_org_features()	Assert QRF output rows == receiver rows
cps.py: add_org_labor_market_inputs()	Assert receiver frame == CPS person count; assert each stored variable == person count
extended_cps.py: _splice_cps_only_predictions()	Assert stage-2 predictions == entity half-length
source_impute.py: _impute_org()	Assert predictions == dataset person count

Downsample fix

CPS.downsample() previously kept un-downsampled arrays for variables not recognized by the current policyengine-us (via continue). Now it drops them, preventing dimension mismatches when new input variables are added.

Test plan

• All 7 test_org.py tests pass
• All 22 test_extended_cps.py tests pass
• CI passes
• Regenerate enhanced_cps_2024.h5 and verify hourly_wage has correct dimensions

🤖 Generated with Claude Code

[MaxGhenis]

Pushed a follow-up commit that broadens this fix beyond the original CPS-only patch.

What changed:

• moved the downsample logic into a shared helper
• made downsample fail closed if the dataset contains variables missing from the active country package
• added an entity-length validation pass before saving the downsampled artifact
• applied the same guardrails to SCF.downsample() so this bug class does not survive there
• added focused regression tests for unknown-variable skew and mismatched entity lengths

I also filed #677 for the remaining release-contract work: exact policyengine-us pinning, pre-publish artifact validation, and a fresh-env Microsimulation() smoke test after build/publication.