Derive current HIS from the regime name for result panels

Add aca_model.results.add_his_from_regime_name: the current health-insurance
state is the regime a subject occupies, encoded as the leading token of the
`{his}_{mc}_{ss}_{canwork}` regime name. `his` is not a per-subject model output,
so it cannot be requested as a pylcm additional_target — downstream panels derive
it from `regime_name` instead.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: hmgaudecker

src/aca_model/results.py

@@ -0,0 +1,24 @@
+"""Post-processing helpers for aca-model simulation result panels."""
+
+import pandas as pd
+
+
+def add_his_from_regime_name(panel: pd.DataFrame) -> pd.DataFrame:
+    """Return `panel` with a `his` column derived from `regime_name`.
+
+    The current health-insurance state is not a per-subject model output — it is
+    the regime a subject occupies. Regime names follow the
+    `{his}_{mc}_{ss}_{canwork}` convention (see
+    `aca_model.baseline.regimes.REGIME_SPECS`), so `his` is the leading
+    underscore-delimited token of `regime_name`. The terminal `dead` regime has
+    no HIS component and maps to `"dead"`, which no HIS moment selects.
+
+    Args:
+        panel: Simulation result DataFrame carrying a `regime_name` column.
+
+    Returns:
+        A copy of `panel` with an added string `his` column.
+
+    """
+    his = panel["regime_name"].astype("str").str.split("_", n=1).str[0].astype("str")
+    return panel.assign(his=his)

tests/test_results.py

@@ -0,0 +1,32 @@
+import pandas as pd
+from pandas.testing import assert_series_equal
+
+from aca_model.results import add_his_from_regime_name
+
+
+def test_add_his_from_regime_name_extracts_leading_token():
+    """`his` is the leading token of `regime_name` (`{his}_{mc}_{ss}_{canwork}`).
+
+    The current health-insurance state is encoded as the first underscore-delimited
+    component of the regime name; the terminal `dead` regime maps to `"dead"`.
+    """
+    panel = pd.DataFrame(
+        {
+            "regime_name": pd.Categorical(
+                [
+                    "retiree_nomc_inelig_canwork",
+                    "tied_dimc_choose_canwork",
+                    "nongroup_oamc_forced_forcedout",
+                    "dead",
+                ]
+            ),
+            "value": [1.0, 2.0, 3.0, 4.0],
+        }
+    )
+
+    result = add_his_from_regime_name(panel)
+
+    assert_series_equal(
+        result["his"],
+        pd.Series(["retiree", "tied", "nongroup", "dead"], name="his"),
+    )