Add ZIP code-level HUD payment standards for Texas

[hua7450]

Summary

Resolves Housing Choice Voucher (HCV) payment standards at the ZIP-code level for Texas, replacing the county-level Fair Market Rent for ~1,118 covered ZIPs. Previously pha_payment_standard only varied by county (plus a hardcoded LA County schedule).

How

pha_payment_standard now resolves from most to least geographically specific:

1. Published ZIP payment standard — zip_code_payment_standard
2. Metro Small Area FMR — small_area_fair_market_rent
3. LA County local schedule — unchanged
4. County FMR — hud_fair_market_rent, unchanged

ZIP paths only fire on a match, so county-level and microsimulation households (where zip_code is unset) are unaffected.

Data

Source	Coverage	Bedrooms	Year
TDHCA published HCV payment standards	284 ZIPs / 34 counties (service-area ring + rural)	0–6	2025
HUD Small Area FMRs (4 mandatory-SAFMR metros: Houston, Dallas, San Antonio, Fort Worth)	834 ZIPs	0–4	FY2026

• TDHCA: parameters/gov/hud/payment_standards/zip_code_payment_standards.csv
• SAFMR: parameters/gov/hud/fmr/small_area_fair_market_rents.csv

Variables

• Filled small_area_fair_market_rent (ZIP→SAFMR lookup) and safmr_used_for_hcv
• Added zip_code_payment_standard (ZIP→published-standard lookup)
• Rewired pha_payment_standard

This also activates the Harris Rent Relief Act contrib reform's SAFMR-based rent cap for the four TX metros — it consumes small_area_fair_market_rent / safmr_used_for_hcv, which were previously stubs (see the changed changelog fragment).

Notes / limitations

• Coverage is the TDHCA service area + the 4 mandatory-SAFMR metro cores. Other TX metros (Austin, El Paso, …) and rural TX keep the county FMR, matching HUD policy (SAFMR is only mandatory in those 4 metros).
• Year labels follow the published data (TDHCA 2025, SAFMR FY2026); the framework imputes the nearest available year.

Verification

• TDHCA CSV re-extracted from the source PDF via two independent engines — all 284 ZIPs × 7 bedrooms match (0 mismatches).
• SAFMR CSV verified against HUD's FY2026 xlsx — all 834 ZIPs × 5 bedrooms match; cross-HMFA dedup confirmed lossless.
• pd.merge order-preservation confirmed on scrambled multi-household vectors.

Test plan

• New unit tests: small_area_fair_market_rent, zip_code_payment_standard, safmr_used_for_hcv, plus precedence cases in pha_payment_standard
• CI passes

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (cf06458) to head (8eff9d6).
⚠️ Report is 14 commits behind head on main.

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files            5         4    -1     
  Lines           73        80    +7     
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+ Hits            73        80    +7     

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unittests	100.00% <100.00%> (ø)

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