Fix dataset param missing from query in set_user_policy

When dataset is truthy, the query builds "AND dataset = ?" (7
placeholders) but the params tuple only contained 6 values — the
dataset value was never appended. This caused a parameter binding
crash when saving a policy with a custom dataset.

Build the params list conditionally so dataset is included when present.

Fixes #3310

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: anth-volk

policyengine_api/endpoints/policy.py

@@ -228,9 +228,13 @@ def set_user_policy(country_id: str) -> dict:
             f"AND dataset {dataset_select_str}"
         )
 
+        params = [country_id, reform_id, baseline_id, user_id, year, geography]
+        if dataset:
+            params.append(dataset)
+
         row = database.query(
             query,
-            (country_id, reform_id, baseline_id, user_id, year, geography),
+            tuple(params),
         ).fetchone()
 
     except Exception as e:

tests/unit/endpoints/test_set_user_policy_dataset.py

@@ -0,0 +1,98 @@
+"""Regression test for issue #3310.
+
+When dataset is truthy in set_user_policy (policy.py:224-237), the query
+builds "AND dataset = ?" (7 placeholders) but the params must include
+the dataset value. Previously, the dataset was never appended, causing
+a parameter binding crash.
+"""
+
+import time
+
+
+def test_set_user_policy_dataset_param_included(test_db):
+    """Verify that the SELECT after INSERT in set_user_policy correctly
+    includes the dataset value in params when dataset is truthy.
+
+    Reproduces the exact code path from policy.py:224-237.
+    """
+    now = int(time.time())
+
+    country_id = "us"
+    reform_id = 2
+    baseline_id = 1
+    user_id = "user1"
+    year = "2025"
+    geography = "us"
+    dataset = "cps"
+
+    # Insert a user_policy with a non-null dataset
+    test_db.query(
+        "INSERT INTO user_policies (country_id, reform_label, reform_id, "
+        "baseline_label, baseline_id, user_id, year, geography, dataset, "
+        "number_of_provisions, api_version, added_date, updated_date) "
+        "VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",
+        (
+            country_id, None, reform_id, None, baseline_id, user_id,
+            year, geography, dataset, 3, "1.0.0", now, now,
+        ),
+    )
+
+    # Reproduce the exact code from policy.py:224-237
+    dataset_select_str = "IS NULL" if not dataset else "= ?"
+    query = (
+        "SELECT * FROM user_policies WHERE country_id = ? AND reform_id = ? "
+        "AND baseline_id = ? AND user_id = ? AND year = ? AND geography = ? "
+        f"AND dataset {dataset_select_str}"
+    )
+
+    params = [country_id, reform_id, baseline_id, user_id, year, geography]
+    if dataset:
+        params.append(dataset)
+
+    # This must not crash — 7 placeholders, 7 params
+    row = test_db.query(query, tuple(params)).fetchone()
+
+    assert row is not None
+    assert row["dataset"] == "cps"
+    assert row["reform_id"] == reform_id
+    assert row["user_id"] == user_id
+
+
+def test_set_user_policy_dataset_null_still_works(test_db):
+    """When dataset is None/falsy, the query uses IS NULL with 6 params."""
+    now = int(time.time())
+
+    country_id = "us"
+    reform_id = 2
+    baseline_id = 1
+    user_id = "user1"
+    year = "2025"
+    geography = "us"
+    dataset = None
+
+    test_db.query(
+        "INSERT INTO user_policies (country_id, reform_label, reform_id, "
+        "baseline_label, baseline_id, user_id, year, geography, dataset, "
+        "number_of_provisions, api_version, added_date, updated_date) "
+        "VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",
+        (
+            country_id, None, reform_id, None, baseline_id, user_id,
+            year, geography, dataset, 3, "1.0.0", now, now,
+        ),
+    )
+
+    dataset_select_str = "IS NULL" if not dataset else "= ?"
+    query = (
+        "SELECT * FROM user_policies WHERE country_id = ? AND reform_id = ? "
+        "AND baseline_id = ? AND user_id = ? AND year = ? AND geography = ? "
+        f"AND dataset {dataset_select_str}"
+    )
+
+    params = [country_id, reform_id, baseline_id, user_id, year, geography]
+    if dataset:
+        params.append(dataset)
+
+    row = test_db.query(query, tuple(params)).fetchone()
+
+    assert row is not None
+    assert row["dataset"] is None