Add survey-aware bootstrap for all estimators (Phase 6)

TODO.md

@@ -52,9 +52,9 @@ Deferred items from PR reviews that were not addressed before merge.
 | ImputationDiD dense `(A0'A0).toarray()` scales O((U+T+K)^2), OOM risk on large panels | `imputation.py` | #141 | Medium (deferred — only triggers when sparse solver fails; fixing requires sparse least-squares alternatives) |
 | EfficientDiD: API docs / tutorial page for new public estimator | `docs/` | #192 | Medium |
 | Multi-absorb weighted demeaning needs iterative alternating projections for N > 1 absorbed FE with survey weights; unweighted multi-absorb also uses single-pass (pre-existing, exact only for balanced panels) | `estimators.py` | #218 | Medium |
-| CallawaySantAnna survey: strata/PSU/FPC rejected at runtime. Full design-based SEs require routing the combined IF/WIF through `compute_survey_vcov()`. Currently weights-only. | `staggered.py` | #233 | Medium |
+| CallawaySantAnna survey: strata/PSU/FPC — **Resolved**. Aggregated SEs now use `compute_survey_if_variance()`. Bootstrap uses PSU-level multiplier weights. | `staggered.py` | #233 | Resolved |
 | CallawaySantAnna survey + covariates + IPW/DR: DRDID panel nuisance-estimation IF corrections not implemented. Currently gated with NotImplementedError. Regression method with covariates works (has WLS nuisance IF correction). | `staggered.py` | #233 | Medium |
-| SyntheticDiD/TROP survey: strata/PSU/FPC deferred. Full design-based bootstrap (Rao-Wu rescaled weights) needed for survey-aware resampling. Currently pweight-only. | `synthetic_did.py`, `trop.py` | — | Medium |
+| SyntheticDiD/TROP survey: strata/PSU/FPC — **Resolved**. Rao-Wu rescaled bootstrap implemented for both. TROP uses cross-classified pseudo-strata. Rust TROP remains pweight-only (Python fallback for full design). | `synthetic_did.py`, `trop.py` | — | Resolved |
 | EfficientDiD hausman_pretest() clustered covariance uses stale `n_cl` after filtering non-finite EIF rows — should recompute effective cluster count and remap indices after `row_finite` filtering | `efficient_did.py` | #230 | Medium |
 | EfficientDiD `control_group="last_cohort"` trims at `last_g - anticipation` but REGISTRY says `t >= last_g`. With `anticipation=0` (default) these are identical. With `anticipation>0`, code is arguably more conservative (excludes anticipation-contaminated periods). Either align REGISTRY with code or change code to `t < last_g` — needs design decision. | `efficient_did.py` | #230 | Low |
 | TripleDifference power: `generate_ddd_data` is a fixed 2×2×2 cross-sectional DGP — no multi-period or unbalanced-group support. Add a `generate_ddd_panel_data` for panel DDD power analysis. | `prep_dgp.py`, `power.py` | #208 | Low |

diff_diff/_backend.py

@@ -13,7 +13,7 @@
 
 # Check for backend override via environment variable
 # DIFF_DIFF_BACKEND can be: 'auto' (default), 'python', or 'rust'
-_backend_env = os.environ.get('DIFF_DIFF_BACKEND', 'auto').lower()
+_backend_env = os.environ.get("DIFF_DIFF_BACKEND", "auto").lower()
 
 # Try to import Rust backend for accelerated operations
 try:
@@ -38,6 +38,7 @@
         # Diagnostics
         rust_backend_info as _rust_backend_info,
     )
+
     _rust_available = True
 except ImportError:
     _rust_available = False
@@ -61,7 +62,7 @@
     _rust_backend_info = None
 
 # Determine final backend based on environment variable and availability
-if _backend_env == 'python':
+if _backend_env == "python":
     # Force pure Python mode - disable Rust even if available
     HAS_RUST_BACKEND = False
     _rust_bootstrap_weights = None
@@ -82,7 +83,7 @@
     _rust_compute_noise_level = None
     _rust_sc_weight_fw = None
     _rust_backend_info = None
-elif _backend_env == 'rust':
+elif _backend_env == "rust":
     # Force Rust mode - fail if not available
     if not _rust_available:
         raise ImportError(
@@ -111,23 +112,23 @@ def rust_backend_info():
 
 
 __all__ = [
-    'HAS_RUST_BACKEND',
-    'rust_backend_info',
-    '_rust_bootstrap_weights',
-    '_rust_synthetic_weights',
-    '_rust_project_simplex',
-    '_rust_solve_ols',
-    '_rust_compute_robust_vcov',
+    "HAS_RUST_BACKEND",
+    "rust_backend_info",
+    "_rust_bootstrap_weights",
+    "_rust_synthetic_weights",
+    "_rust_project_simplex",
+    "_rust_solve_ols",
+    "_rust_compute_robust_vcov",
     # TROP estimator acceleration (local method)
-    '_rust_unit_distance_matrix',
-    '_rust_loocv_grid_search',
-    '_rust_bootstrap_trop_variance',
+    "_rust_unit_distance_matrix",
+    "_rust_loocv_grid_search",
+    "_rust_bootstrap_trop_variance",
     # TROP estimator acceleration (global method)
-    '_rust_loocv_grid_search_global',
-    '_rust_bootstrap_trop_variance_global',
+    "_rust_loocv_grid_search_global",
+    "_rust_bootstrap_trop_variance_global",
     # SDID weights (Frank-Wolfe matching R's synthdid)
-    '_rust_sdid_unit_weights',
-    '_rust_compute_time_weights',
-    '_rust_compute_noise_level',
-    '_rust_sc_weight_fw',
+    "_rust_sdid_unit_weights",
+    "_rust_compute_time_weights",
+    "_rust_compute_noise_level",
+    "_rust_sc_weight_fw",
 ]