# Contract (F2-dev-01)
- Question: within-firm, within-year slope beta of y on x in TWFE model y_it = a_i + g_t + beta x_it + u_it (balanced simulated firm-year panel).
- Estimands: beta (TWFE slope). Meaningful under strict exogeneity of x conditional on a_i, g_t; linear additive effects. Uncertainty: cluster-robust by firm (independence across firms, arbitrary within-firm dependence); also conventional SE, and naive pooled OLS slope as baseline.
- Outputs: out/results.json (task_id, beta_pooled, beta_fe, se_conventional, se_cluster, beta_ci_low, beta_ci_high, n_firms, n_years, n_analysed, feasibility, feasibility_reason, data_issues, n_input_rows, random_seed); out/report.md (Question; Data and exclusions; Method; Results; Uncertainty; Limitations and open issues); out/analysis.py; out/claims.json.
- Information rule: only data/firm_panel.csv.
- Invalid/impossible if: duplicate firm-years unresolvable, x has no within variation after FE, too few clusters, missing columns.