+- **`SpilloverDiD(survey_design=...)` integration on HC1 / CR1 paths via Binder TSL (Wave E.1).** Lifts the Wave B/C/D upfront `NotImplementedError` and adds design-based variance for `vcov_type ∈ {"hc1"}` plus `cluster=<col>` (CR1). **Documented synthesis** of Gerber (2026, arXiv:2605.04124) Proposition 1 — Binder Taylor Series Linearization for IF representations of smooth functionals; explicitly derived for TwoStageDiD in the paper's Appendix — composed with the Wave D Gardner GMM first-stage uncertainty correction (Butts 2021 §3.1 + Gardner 2022 §4) applied to SpilloverDiD's ring-indicator stage-2 design. No reference software combines all ingredients. **Mechanical composition:** SpilloverDiD's per-obs Wave D IF `psi_i = gamma_hat' * X_{10,i} * eps_{10,i} - X_{2,i} * eps_{2,i}` (with survey weights threaded through `gamma_hat` solve, eps construction, and bread inversion via Hájek normalization) is aggregated to PSU totals and passed to the audited `_compute_stratified_meat_from_psu_scores` Binder TSL meat helper. Stage-1 FE estimation extends `_iterative_fe_subset` with a `weights=` kwarg implementing WLS-FE via weighted bincount (numerator `bincount(w*resid)` / denominator `bincount(w)`); the `weights is None` path is bit-identical to the Wave B / C / D unweighted bincount. **Degrees of freedom:** t-distribution lookup uses `ResolvedSurveyDesign.df_survey` (4-way branch: PSU+strata → `n_PSU - n_strata`; PSU only → `n_PSU - 1`; strata only → `n_obs - n_strata`; neither → `n_obs - 1`), threaded through all four `safe_inference` call sites (aggregate `tau_total`, per-ring `delta_j`, event-study per-event-time `tau_k` / `delta_jk`, scalar `att` lincom). **Survey-array subsetting:** when `finite_mask` drops baseline-treated rows, `survey_weights` and `ResolvedSurveyDesign.{weights, strata, psu, fpc, replicate_weights}` are subsetted in parallel; `n_psu`, `n_strata`, and `survey_metadata` are recomputed (mirrors `TwoStageDiD.fit:567-601`). **Cluster + survey resolution:** when `cluster=<col>` and `survey_design.psu` are both supplied, a `UserWarning` fires and PSU wins (mirrors `_resolve_effective_cluster` at `survey.py:1253-1275`; TwoStageDiD parity). When `cluster=<col>` is supplied without `survey_design.psu`, the cluster column is injected as the effective PSU via `_inject_cluster_as_psu`, which now honors `SurveyDesign.nest`: under `nest=False`, cluster labels must be globally unique across strata (raises if they repeat, matching the explicit-PSU resolver's contract). **Saturated `df_survey = 0` NaN-fail:** when `lonely_psu="remove"` removes all strata (singleton PSUs), the meat helper returns `(_, var_computed=False, legit_zero=0)` and SpilloverDiD's Wave E.1 path returns NaN meat with a `UserWarning` matching `"df_survey"` so callers can `pytest.warns(UserWarning, match="df_survey")`. This is a **departure from TwoStageDiD** (`two_stage.py:2003-2005`) which currently NaN-fails SILENTLY; Wave E.1 surfaces the diagnostic per `feedback_no_silent_failures`. **Public surface restrictions:** `vcov_type="conley" + survey_design=` raises `NotImplementedError` pointing at planned Wave E.2 (Conley × survey product-kernel synthesis with within-stratum Conley sandwich on PSU totals); replicate-weight variance (BRR / Fay / JK1 / JKn / SDR) raises `NotImplementedError` — per Gerber (2026) Appendix A, the IF-reweighting shortcut does not apply to TwoStageDiD-class estimators because `gamma_hat` is weight-sensitive; correct support requires per-replicate full re-fit and is queued as a follow-up; non-pweight (`weight_type ∈ {"fweight", "aweight"}`) raises `ValueError` (the Binder TSL assumes probability weights). **Implementation:** `_compute_gmm_corrected_meat` extended with `survey_weights` + `resolved_survey` kwargs at `diff_diff/two_stage.py:56` (TYPE_CHECKING forward reference for `ResolvedSurveyDesign` to avoid circular import); new module-level helper `_compute_binder_tsl_meat` at `diff_diff/two_stage.py` wraps `_compute_stratified_meat_from_psu_scores` with implicit per-obs PSU synthesis for no-PSU survey designs + the Wave E.1 NaN-fail + warning; `_iterative_fe_subset` weighted path at `diff_diff/spillover.py:1382` (in-place extension, bit-identical fallback, positive-weight identification gate); `_inject_cluster_as_psu` honors `nest` (shared survey-helper fix that also benefits TwoStageDiD); `ResolvedSurveyDesign` gains a `nest` field propagated through all 5 construction sites. `SpilloverDiDResults` extended with `survey_metadata`, `n_psu`, `n_strata` fields at `diff_diff/results.py`. **Tests:** new `TestSpilloverDiDWaveE1SurveyDesignHc1` (17 tests: bit-identity fallback, Binder TSL hand-check uniform + non-uniform weights, lonely_psu modes, FPC degenerate limits ×3, saturated NaN-fail with `pytest.warns(match="df_survey")`, cluster+survey warn-and-use-PSU, no-PSU regressions (weights-only, weights+strata, cluster-without-PSU, cluster overlap with nest=False/True), zero-weight Omega_0 exclusion + all-zero raises, replicate-weight + non-pweight + Conley+survey rejections, fit idempotency, finite_mask subsetting) and `TestSpilloverDiDWaveE1SurveyDesignEventStudy` (7 tests: event-study + survey on both `is_staggered` branches with `df_survey` lincom verification, distinguishability between survey-share and sample-share lincom rules via manual reconstruction with cohort-correlated weights + non-constant tau_k, aggregate-vs-event-study parity, drift goldens, subset-path invariant). Wave B/C/D bullets below are unchanged; this entry replaces the pre-Wave-E.1 `survey_design=` rejection.
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