Rename TROP method="twostep" to method="local" with deprecation

Rename the per-observation TROP method from "twostep" to "local",
forming a natural local/global pair. Both "twostep" and "joint" are
now deprecated aliases (removal in v3.0). Also rename internal
_joint_* methods to _global_* and Rust exports for consistency.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: igerber

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+- Rename TROP `method="twostep"` to `method="local"`; `"twostep"` deprecated, removal in v3.0
+- Rename internal TROP `_joint_*` methods to `_global_*` for consistency
+
 ## [2.7.1] - 2026-03-15
 
 ### Changed

CLAUDE.md

@@ -122,7 +122,7 @@ category (`Methodology/Correctness`, `Performance`, or `Testing/Docs`):
   `threshold = 0.40 if n_boot < 100 else 0.15`.
 - **`assert_nan_inference()`** from conftest.py: Use to validate ALL inference fields are
   NaN-consistent. Don't check individual fields separately.
-- **Slow tests**: TROP methodology/joint-method tests, Sun-Abraham bootstrap, and
+- **Slow tests**: TROP methodology/global-method tests, Sun-Abraham bootstrap, and
   TROP-parity tests are marked `@pytest.mark.slow` and excluded by default via `addopts`.
   `test_trop.py` uses per-class markers (not file-level) so that validation, API, and
   solver tests still run in the pure Python CI fallback. Run `pytest -m ''` to include

README.md

@@ -1517,7 +1517,7 @@ trop = TROP(
 
 ```python
 TROP(
-    method='twostep',           # Estimation method: 'twostep' (default) or 'joint'
+    method='local',             # Estimation method: 'local' (default) or 'global'
     lambda_time_grid=None,      # Time decay grid (default: [0, 0.1, 0.5, 1, 2, 5])
     lambda_unit_grid=None,      # Unit distance grid (default: [0, 0.1, 0.5, 1, 2, 5])
     lambda_nn_grid=None,        # Nuclear norm grid (default: [0, 0.01, 0.1, 1, 10])
@@ -1530,8 +1530,8 @@ TROP(
 ```
 
 **Estimation methods:**
-- `'twostep'` (default): Per-observation model fitting following Algorithm 2 of the paper. Computes observation-specific weights and fits a model for each treated observation, then averages the individual treatment effects. More flexible but computationally intensive.
-- `'joint'`: Joint weighted least squares optimization. Estimates a single scalar treatment effect τ along with fixed effects and optional low-rank factor adjustment. Faster but assumes homogeneous treatment effects.
+- `'local'` (default): Per-observation model fitting following Algorithm 2 of the paper. Computes observation-specific weights and fits a model for each treated observation, then averages the individual treatment effects. More flexible but computationally intensive.
+- `'global'`: Global weighted least squares optimization. Fits a single model on control observations with global weights, then computes per-observation treatment effects as residuals. Faster but uses global rather than observation-specific weights.
 
 **Convenience function:**
 

diff_diff/_backend.py

@@ -23,13 +23,13 @@
         project_simplex as _rust_project_simplex,
         solve_ols as _rust_solve_ols,
         compute_robust_vcov as _rust_compute_robust_vcov,
-        # TROP estimator acceleration (twostep method)
+        # TROP estimator acceleration (local method)
         compute_unit_distance_matrix as _rust_unit_distance_matrix,
         loocv_grid_search as _rust_loocv_grid_search,
         bootstrap_trop_variance as _rust_bootstrap_trop_variance,
-        # TROP estimator acceleration (joint method)
-        loocv_grid_search_joint as _rust_loocv_grid_search_joint,
-        bootstrap_trop_variance_joint as _rust_bootstrap_trop_variance_joint,
+        # TROP estimator acceleration (global method)
+        loocv_grid_search_global as _rust_loocv_grid_search_global,
+        bootstrap_trop_variance_global as _rust_bootstrap_trop_variance_global,
         # SDID weights (Frank-Wolfe matching R's synthdid)
         compute_sdid_unit_weights as _rust_sdid_unit_weights,
         compute_time_weights as _rust_compute_time_weights,
@@ -46,13 +46,13 @@
     _rust_project_simplex = None
     _rust_solve_ols = None
     _rust_compute_robust_vcov = None
-    # TROP estimator acceleration (twostep method)
+    # TROP estimator acceleration (local method)
     _rust_unit_distance_matrix = None
     _rust_loocv_grid_search = None
     _rust_bootstrap_trop_variance = None
-    # TROP estimator acceleration (joint method)
-    _rust_loocv_grid_search_joint = None
-    _rust_bootstrap_trop_variance_joint = None
+    # TROP estimator acceleration (global method)
+    _rust_loocv_grid_search_global = None
+    _rust_bootstrap_trop_variance_global = None
     # SDID weights (Frank-Wolfe matching R's synthdid)
     _rust_sdid_unit_weights = None
     _rust_compute_time_weights = None
@@ -69,13 +69,13 @@
     _rust_project_simplex = None
     _rust_solve_ols = None
     _rust_compute_robust_vcov = None
-    # TROP estimator acceleration (twostep method)
+    # TROP estimator acceleration (local method)
     _rust_unit_distance_matrix = None
     _rust_loocv_grid_search = None
     _rust_bootstrap_trop_variance = None
-    # TROP estimator acceleration (joint method)
-    _rust_loocv_grid_search_joint = None
-    _rust_bootstrap_trop_variance_joint = None
+    # TROP estimator acceleration (global method)
+    _rust_loocv_grid_search_global = None
+    _rust_bootstrap_trop_variance_global = None
     # SDID weights (Frank-Wolfe matching R's synthdid)
     _rust_sdid_unit_weights = None
     _rust_compute_time_weights = None
@@ -118,13 +118,13 @@ def rust_backend_info():
     '_rust_project_simplex',
     '_rust_solve_ols',
     '_rust_compute_robust_vcov',
-    # TROP estimator acceleration (twostep method)
+    # TROP estimator acceleration (local method)
     '_rust_unit_distance_matrix',
     '_rust_loocv_grid_search',
     '_rust_bootstrap_trop_variance',
-    # TROP estimator acceleration (joint method)
-    '_rust_loocv_grid_search_joint',
-    '_rust_bootstrap_trop_variance_joint',
+    # TROP estimator acceleration (global method)
+    '_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',