Apportionment workpaper: factor sourcing rules and tie-outs

Build an apportionment workpaper for {company_name} for {tax_year}.

Inputs:
- Sales by state and sourcing basis: {sales_by_state}
- Payroll by state: {payroll_by_state}
- Property by state: {property_by_state}
- State-specific factor rules (if known): {state_factor_rules}
- Tie-out sources (GL, payroll system): {tieout_sources}

Output:
1) Workpaper template with factor calculations and state inputs.
2) Tie-out steps and recon tables to source systems.
3) Exception checks (negative factors, missing states, inconsistent definitions).
4) Documentation checklist for audit defense.

Flag where state-specific rules may change outcomes.