Halve lesson gain when the bag has no textbook for the subject.

Locker and home do not count. A pack without the field keeps vanilla 0.5.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/HSchool.Content.Tests/BehaviorDefTests.cs

@@ -64,6 +64,39 @@ public class BehaviorDefTests
         Assert.Contains("carry mass", error.Message, StringComparison.OrdinalIgnoreCase);
     }
 
+    [Fact]
+    public void MissingLessonNoTextbookFactor_DefaultsToHalf()
+    {
+        var catalog = _loader.Load(
+            [CatalogLoader.CorePackId],
+            [
+                PackDocuments.Def(
+                    CatalogLoader.CorePackId,
+                    "behavior",
+                    "rules",
+                    """{ "defName": "Behavior", "needThreshold": 0.35, "lessonSkillPerHour": 0.05, "commuteSlackMin": 0, "commuteSlackMax": 6, "switchMargin": 0.15 }"""),
+            ]);
+
+        Assert.NotNull(catalog.BehaviorRules);
+        Assert.Equal(0.5f, catalog.BehaviorRules.LessonNoTextbookFactor);
+    }
+
+    [Fact]
+    public void LessonNoTextbookFactor_OutOfRange_FailsTheCatalog()
+    {
+        var error = Assert.Throws<ContentLoadException>(() => _loader.Load(
+            [CatalogLoader.CorePackId],
+            [
+                PackDocuments.Def(
+                    CatalogLoader.CorePackId,
+                    "behavior",
+                    "rules",
+                    """{ "defName": "Behavior", "lessonNoTextbookFactor": 1.5 }"""),
+            ]));
+
+        Assert.Contains("lessonNoTextbookFactor", error.Message, StringComparison.Ordinal);
+    }
+
     [Fact]
     public void NegativeApparelWear_FailsTheCatalog()
     {