Fix CI review Round 6: joiners_leavers n_obs, stale docstrings

P1: Fix to_dataframe("joiners_leavers") overall row n_obs: use
    n_treated_obs when joiners/leavers are suppressed (non-binary)
    instead of summing zeroed joiner/leaver obs counts.
P2: Add joiners_leavers and summary() assertions to
    test_nonbinary_lmax1_renderer_contract.
P3: Update to_dataframe() docstring: event_study/normalized available
    at L_max >= 1 (was >= 2).

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

Author: igerber

diff_diff/chaisemartin_dhaultfoeuille_results.py

@@ -788,9 +788,9 @@ def to_dataframe(self, level: str = "overall") -> pd.DataFrame:
               the A11-zeroed flags.
             - ``"event_study"``: one row per horizon (positive and
               negative/placebo), including a reference period at
-              horizon 0. Available when ``L_max >= 2``.
+              horizon 0. Available when ``L_max >= 1``.
             - ``"normalized"``: one row per horizon for the normalized
-              effects ``DID^n_l``. Available when ``L_max >= 2``.
+              effects ``DID^n_l``. Available when ``L_max >= 1``.
             - ``"twfe_weights"``: per-(group, time) TWFE decomposition
               weights table. Only available when ``twfe_diagnostic=True``
               was passed to ``fit()``.
@@ -847,7 +847,11 @@ def to_dataframe(self, level: str = "overall") -> pd.DataFrame:
                     "conf_int_lower": self.overall_conf_int[0],
                     "conf_int_upper": self.overall_conf_int[1],
                     "n_cells": self.n_switcher_cells,
-                    "n_obs": self.n_joiner_obs + self.n_leaver_obs,
+                    "n_obs": (
+                        self.n_treated_obs
+                        if not self.joiners_available and not self.leavers_available
+                        else self.n_joiner_obs + self.n_leaver_obs
+                    ),
                     "available": True,
                 },
                 {

tests/test_chaisemartin_dhaultfoeuille.py

@@ -2454,6 +2454,14 @@ def test_nonbinary_lmax1_renderer_contract(self):
         # Joiners/leavers unavailable for non-binary
         assert r.joiners_available is False
         assert r.leavers_available is False
+        # to_dataframe("joiners_leavers"): overall row n_obs should be > 0
+        df_jl = r.to_dataframe("joiners_leavers")
+        overall_row = df_jl[df_jl["estimand"] == "DID_1"]
+        assert len(overall_row) == 1
+        assert overall_row.iloc[0]["n_obs"] > 0
+        # summary() should contain "DID_1" label
+        s = r.summary()
+        assert "DID_1" in s
 
     def test_twfe_diagnostic_skipped_nonbinary(self):
         """TWFE diagnostic should be skipped (with warning) for non-binary."""