LWDiD precursor: canonical LW paper reviews + REGISTRY entry + Prop 99 / Walmart dataset loaders

.gitignore

@@ -74,6 +74,9 @@ target/
 .claude/paper-review/
 .claude/scheduled_tasks.lock
 
+# Playwright MCP browser-session artifacts
+.playwright-mcp/
+
 # MCP configuration (may contain tokens)
 .mcp.json
 

CHANGELOG.md

@@ -48,6 +48,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ignores) with `warn_unused_ignores = true` to keep them from going stale — 23
   already-stale ignores were removed. Tightening tracked in TODO.md. No public
   API or numerical behavior change.
+- **`load_prop99` + `load_walmart` dataset loaders.** California Proposition 99
+  smoking panel (39 states, single treated unit, Lee-Wooldridge cohort format) and
+  the Walmart entry county panel (1,277 counties, staggered 1986-1999 openings,
+  Brown & Butts CBP construction), downloaded with local caching from the
+  MIT-licensed ancillary data of the authors' Stata `lwdid` package (SSC).
+  Every byte-load is verified against a pinned SHA-256 and the parsed panels are
+  validated against their source invariants; if the real data cannot be obtained,
+  a seeded same-schema synthetic fallback is returned with an explicit
+  `UserWarning` and `df.attrs["source"] = "synthetic_fallback"`.
 - **Internal: rdrobust sharp-RD bandwidth-selection port (`diff_diff/_rdrobust_port.py`).**
   Step-1 machinery for the `RegressionDiscontinuity` estimator above: a faithful
   pure-Python NumPy/SciPy port of R `rdrobust` 4.0.0's `rdbwselect` sharp-RD path (all 10 data-driven

TODO.md

@@ -50,6 +50,7 @@ generic sparse-FE, QR+SVD rank-detection redundancy, `check_finite` bypass — m
 | ChangesInChanges/QDiD tutorial notebook (2x2 distributional walkthrough: QTE grid, interior range, uniform bands, CiC-vs-QDiD comparison) - deferred from the implementation PR as a documented decision. | `docs/tutorials/` | #682 | Mid | Low |
 | Tighten the mypy suppressions that back the enforced-zero posture: burn down `prep_dgp`'s per-module `[index]` override (needs a None-vs-array restructure that preserves the seeded RNG stream), and evaluate re-enabling the globally disabled codes (`arg-type`, `return-value`, `var-annotated`, `assignment`) one at a time — `assignment` alone hid several real annotation drifts found during the 2026-07 triage. | `pyproject.toml` `[tool.mypy]`, `diff_diff/prep_dgp.py` | lint-CI | Mid | Low |
 | `practitioner_next_steps()` dedicated handler for `ChangesInChangesResults` (currently falls back to `_handle_generic`, which is safe; a dedicated handler is the established full-integration step, cf. HAD Phase 5). | `diff_diff/practitioner.py` | #682 | Quick | Low |
+| Align the four legacy dataset loaders (`load_card_krueger`, `load_castle_doctrine`, `load_divorce_laws`, `load_mpdta`) with the loud-fallback pattern of `load_prop99`/`load_walmart`: `UserWarning` + `df.attrs["source"]` marker on synthetic fallback (currently silent), plus optional checksum pinning for the CSV downloads. | `diff_diff/datasets.py` | LWDiD precursor | Quick | Low |
 
 ---
 

diff_diff/__init__.py

@@ -72,6 +72,8 @@
     load_dataset,
     load_divorce_laws,
     load_mpdta,
+    load_prop99,
+    load_walmart,
 )
 from diff_diff.diagnostic_report import (
     DIAGNOSTIC_REPORT_SCHEMA_VERSION,
@@ -537,6 +539,8 @@
     "load_castle_doctrine",
     "load_divorce_laws",
     "load_mpdta",
+    "load_prop99",
+    "load_walmart",
     "load_dataset",
     "list_datasets",
     "clear_cache",