Fix: add retention to validation allowlists in validate_model and validate_metric

Author: nicosuave

sidemantic/validation.py

@@ -88,7 +88,7 @@ def validate_model(model: "Model") -> list[str]:
     # Derived, ratio, cumulative, time_comparison, and conversion metrics don't need agg
     for measure in model.metrics:
         # Skip validation for complex metric types that don't use agg
-        if measure.type in ["derived", "ratio", "cumulative", "time_comparison", "conversion"]:
+        if measure.type in ["derived", "ratio", "cumulative", "time_comparison", "conversion", "retention"]:
             continue
 
         valid_aggs = _valid_measure_aggs()
@@ -126,10 +126,11 @@ def validate_metric(measure: "Metric", graph: "SemanticGraph") -> list[str]:
         "cumulative",
         "time_comparison",
         "conversion",
+        "retention",
     ]:
         errors.append(
             f"Metric '{measure.name}' has invalid type '{measure.type}'. "
-            f"Must be one of: ratio, derived, cumulative, time_comparison, conversion"
+            f"Must be one of: ratio, derived, cumulative, time_comparison, conversion, retention"
         )
         return errors  # Can't continue validation with invalid type
 
@@ -191,6 +192,12 @@ def validate_metric(measure: "Metric", graph: "SemanticGraph") -> list[str]:
         if not measure.sql and not measure.window_expression:
             errors.append(f"Cumulative measure '{measure.name}' must have 'sql' or 'window_expression' defined")
 
+    elif measure.type == "retention":
+        if not measure.entity:
+            errors.append(f"Retention measure '{measure.name}' must have 'entity' defined")
+        if not measure.cohort_event:
+            errors.append(f"Retention measure '{measure.name}' must have 'cohort_event' defined")
+
     return errors