CECL allowance model governance: assumptions, controls, and doc

Create a CECL (allowance for credit losses) governance package for {institution_name}.

Inputs:
- Portfolio segmentation: {portfolio_segmentation}
- Model approach (PD/LGD, vintage, WARM): {model_approach}
- Key assumptions and forecasts: {assumptions_forecasts}
- Data sources and quality notes: {data_sources_quality}
- Validation history (if any): {validation_history}

Output:
1) Model governance framework (roles, approvals, change control).
2) Assumptions documentation template (what, why, evidence, sensitivity).
3) Control matrix (data completeness, model runs, overrides, management review).
4) Validation/testing plan (backtesting, benchmarking).
5) Audit-ready workpaper index.

Keep it practical; do not invent model parameters.