Review of "Add data preparation utilities for easier onboarding" with:
- 9 specific issues identified (4 medium, 5 low priority)
- Performance issue: iterrows() in wide_to_long should use pd.melt()
- Bug: groupby().ffill() doesn't work as expected in balance_panel
- Logic issue: multi-period validation incomplete
- Missing test coverage for ffill path
- Overall positive assessment with requested changes

Both PR #9 and PR #10 review feedback has been addressed:

PR #9 fixes verified:
- Optional type hint added to cluster parameter
- significance_stars property used in __repr__
- Clarifying comments added for vcov computation
- LinAlgError imported directly

PR #10 fixes verified:
- iterrows() replaced with pd.melt() in wide_to_long
- groupby().ffill() bug fixed in balance_panel
- Multi-period validation logic corrected
- Index labeling fixed for non-0/1 time values
- np.isinf() guard added for non-numeric types
- Test added for balance_panel ffill path

- Add detailed explanation in Section 14 of why pre-treatment effects
  differ between Callaway-Sant'Anna (varying base) and Sun-Abraham
  (fixed reference period e=-1), while post-treatment effects match
- Enhance comparison code to show CS with both base_period options
- Add point #10 to tutorial summary documenting expected behavior
- Add test documenting this methodological difference
- Update REGISTRY.md with cross-reference note

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

…StageDiD

Addresses axis-C findings #8, #9, and #10 from the silent-failures audit:
three sites where a sparse factorization failure silently fell back to
dense lstsq without any user-facing signal.

- diff_diff/imputation.py:1516 (variance path: scipy.sparse.linalg.spsolve
  on (A_0' W A_0) z = A_1' w). Bare `except Exception` was swallowing
  the root cause before dense lstsq. Now emits a UserWarning identifying
  the exception type and explaining the fallback implication.
- diff_diff/two_stage.py:1647 (GMM sandwich: sparse_factorized on
  X'_{10} W X_{10} for Stage 1 normal equations). `except RuntimeError`
  was silent; now emits a UserWarning.
- diff_diff/two_stage_bootstrap.py:134 (bootstrap path: same pattern as
  above). `except RuntimeError` was silent; now emits a UserWarning.

All three are single-call sites (per fit, or per aggregation level, or
per bootstrap replicate at most a handful of times) so no aggregation
wrapper pattern is needed — one warning per fallback event is
appropriate.

REGISTRY.md updated under ImputationDiD and TwoStageDiD.

New tests (3): monkey-patch the sparse entry point to raise a
RuntimeError, run .fit(), assert the UserWarning fires with the
expected message prefix. Works against both the variance and bootstrap
surfaces.

Axis-C baseline: 3 major silent-fallback sites (imputation, two_stage,
two_stage_bootstrap) -> 0 remaining in these files. PowerAnalysis
simulation counter (finding #11) and ContinuousDiD B-spline (#12)
still open as separate follow-ups.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Lift the gate at chaisemartin_dhaultfoeuille.py:1233-1239 so per-path
event-study effects compose with survey_design under analytical
Binder TSL SE and replicate-weight bootstrap variance. Multiplier
bootstrap (n_bootstrap > 0) under survey + by_path remains gated;
the survey-aware perturbation pivot for path-restricted IFs is
methodologically underived and deferred to a future wave.

Per-path SE routes through the existing _survey_se_from_group_if
cell-period allocator. The per-period IF (U_pp_l_path) with non-path
switcher contributions zeroed at both group and cell levels (the
row-sum identity U_pp.sum(axis=1) == U is preserved trivially under
group-level zeroing) is cohort-recentered via
_cohort_recenter_per_period, then expanded to observations as
psi_i = U_pp[g_i, t_i] * (w_i / W_{g_i, t_i}). Replicate-weight
designs unconditionally use the cell allocator (Class A contract,
PR #323).

New _refresh_path_inference helper post-call refreshes safe_inference
on every populated entry across multi_horizon_inference,
placebo_horizon_inference, path_effects, and path_placebos so all
four surfaces reflect the same final df_survey after per-path
replicate fits append n_valid to the shared accumulator.

Path-enumeration ranking under survey_design remains unweighted
(group-cardinality, not population-weight mass). Lonely-PSU policy
stays sample-wide. Telescope invariant holds bit-exactly: on a
single-path panel, per-path SE matches the global non-by_path
survey SE.

No R parity — R did_multiplegt_dyn does not support survey
weighting; this is a Python-only methodology extension.

14 new tests across two test classes:
- TestByPathSurveyDesignAnalytical: gate dispatch, anti-regression
  on global TSL+bootstrap (locks per-path-only gate scope), per-path
  analytical SE, single-path telescope, replicate-weight SE,
  df_survey propagation, per-path placebos, trends_linear cumulated
  SE inheritance, unobserved-path warnings under survey.
- TestByPathSurveyDesignTelescope: single-path telescoping
  invariant for analytical TSL.

Documentation: REGISTRY.md "Per-path survey-design SE" sub-paragraph;
by_path / paths_of_interest docstrings updated; CHANGELOG entry;
docs/api/chaisemartin_dhaultfoeuille.rst and llms-full.txt updated.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Compose by_path / paths_of_interest with survey_design (Wave 4 #10)

Closes the WooldridgeDiD (ETWFE) methodology-review-tracker
promotion in METHODOLOGY_REVIEW.md (In Progress → Complete),
following the primary-source review for Wooldridge (2025) merged
in PR-A (#484). Adds two paper-driven implementation surfaces and
extends R-parity goldens to the nonlinear paths.

Implementation:
- `aggregate(weights="cohort_share")` on WooldridgeDiDResults
  implements paper Eqs. 7.4 (simple-overall) and 7.6 (event-time,
  restricted to k>=0) cohort-share aggregation weights as an
  opt-in alternative to the default cell-count weighting
  (matching Stata `jwdid_estat`). Inference fields fail-closed to
  NaN with UserWarning per paper Section 7.5 conditional-on-shares
  semantics; raises on `survey_design` (design-consistent totals
  deferred); raises on `type ∈ {"group","calendar"}` (no paper
  closed-form); raises on bootstrap fits (no matching bootstrap
  variant). Closes TODO row 95.
- `cohort_trends=True` on `WooldridgeDiD.__init__` adds linear
  `dg_i · t` cohort-specific trend interactions (paper Section 8
  / Eq. 8.1) for the OLS path. Rejects on logit/poisson per
  paper Section 8 OLS scope; rejects on survey_design pending
  full-dummy/TSL validation; enforces per-cohort pre-period
  identification check (≥ 2 observed pre-periods per treated
  cohort). Auto-routes to full-dummy mode regardless of
  vcov_type. Closes the PR-A Requirements Checklist
  heterogeneous-trends gap.

Tests:
- `tests/test_methodology_wooldridge.py` extended with 6
  paper-equation-numbered methodology classes (Theorem 3.1,
  Proposition 5.1, Section 6 event study, Section 7 aggregation
  paths, Section 8 heterogeneous trends, Section 10 unbalanced
  panels) + `TestW2025LibraryDeviations` consolidating 5 surviving
  deviations. Mirrors the HAD PR #473 precedent.
- Two new R-parity surface classes (`TestWooldridgeParityRPoisson`,
  `TestWooldridgeParityRLogit`) lock the structural surface
  against R `etwfe(family=...)` log-link goldens.
- 209 tests total (60 methodology + 149 R-parity + unit
  regressions).

R Goldens:
- `benchmarks/R/generate_wooldridge_golden.R` extended with
  Poisson + logit DGPs via R `etwfe`; augmented panel CSV
  retains the same seed-generated `y_pois` + `y_logit` columns
  for cross-language reproducibility.
- `benchmarks/R/requirements.R` pins `etwfe >= 0.5.0`.

Tracker promotion:
- METHODOLOGY_REVIEW.md L52 status flip with merge date; detail
  section L583-605 rewritten to the Verified Components / Test
  Coverage / Corrections Made / Deviations / Outstanding
  Concerns template mirroring HAD / ContinuousDiD / DCDH. L27
  example re-pointed; priority queue items #7-#10 renumbered to
  #6-#9.
- REGISTRY.md `## WooldridgeDiD (ETWFE)` extended with
  `### Deviations from the paper / from R / library extensions`
  block consolidating 7 surviving deviations + opt-in notes for
  cohort_share + cohort_trends + survey rejection + bootstrap
  cohort_share rejection contracts.
- CHANGELOG.md `[Unreleased]` `### Added` documents the new
  parameters, R-parity extension, and tracker flip.
- `docs/methodology/papers/wooldridge-2025-review.md`
  Requirements Checklist + Gaps & Uncertainties items 1 + 11
  marked `**Status:** Closed in PR-B`.
- `docs/api/wooldridge_etwfe.rst` updated with weighting-scheme
  notes alongside the existing aggregation table.

Second of two PRs for the WooldridgeDiD methodology-review-tracker
promotion. PR-A merged at e416aed (#484).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Flip the ChaisemartinDHaultfoeuille (DCDH) row from In Progress to
Complete. Adds the Verified Components / Test Coverage / Corrections
Made / Deviations / Outstanding Concerns detail section mirroring the
ContinuousDiD (PR igerber#476) and HAD (PR igerber#473) precedents. Consolidates 7
DCDH deviations from the paper, from R DIDmultiplegtDYN, and library
extensions into a labeled REGISTRY surface per the AI-review
"Documenting Deviations" convention. CHANGELOG [Unreleased] gains a
new Added entry. L27 In Progress example re-pointed to WooldridgeDiD;
L1289 priority-order queue item igerber#6 removed and items igerber#7-igerber#11
renumbered to igerber#6-igerber#10.

No source code changes, no new tests, no new docstrings —
documentation consolidation only.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>