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.Ai.Tests/LessonLearningTests.cs

@@ -1,4 +1,5 @@
 using HSchool.Content;
+using HSchool.People;
 
 namespace HSchool.Ai.Tests;
 
@@ -97,6 +98,40 @@ public class LessonLearningTests
 
         Assert.Equal(explicitWarm, implied);
     }
+
+    [Fact]
+    public void MissingTextbook_HalvesGain()
+    {
+        var withBook = LessonLearning.Gain(50, Math, 1, 0.05f, 1f, 1f, 0, 100, warmth: 1f, textbookFactor: 1f);
+        var without = LessonLearning.Gain(50, Math, 1, 0.05f, 1f, 1f, 0, 100, warmth: 1f, textbookFactor: 0.5f);
+
+        Assert.Equal((withBook - 50) * 0.5f, without - 50, precision: 5);
+    }
+
+    [Fact]
+    public void TextbookInBag_OnlyThatSubjectCounts()
+    {
+        var items = new[]
+        {
+            new InventoryItem("Textbook", null, 1f, ItemLocations.Bag, "Literature"),
+            new InventoryItem("Textbook", null, 1f, ItemLocations.Locker, "Mathematics"),
+        };
+
+        Assert.False(LessonLearning.HasTextbookInBag(items, "Mathematics"));
+        Assert.True(LessonLearning.HasTextbookInBag(items, "Literature"));
+    }
+
+    [Fact]
+    public void TextbookAtHome_DoesNotCount()
+    {
+        var items = new[]
+        {
+            new InventoryItem("Textbook", null, 1f, ItemLocations.Home, "Mathematics"),
+        };
+
+        Assert.False(LessonLearning.HasTextbookInBag(items, "Mathematics"));
+    }
+
     [Fact]
     public void MissingTeacherSkill_UsesRangeMin_AndStillGains()
     {

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()
     {

tests/HSchool.Simulation.Tests/LessonTeacherPresentTests.cs

@@ -238,6 +238,96 @@ public class LessonTeacherPresentTests
         }
     }
 
+    [Fact]
+    public void TextbookInBag_GainsFull()
+    {
+        var (school, homeroom, pupilId, teacherId) = StaffedMath();
+        using (school)
+        {
+            AdvanceTo(school, LessonStart);
+            SetPlace(school, pupilId, homeroom);
+            SetPlace(school, teacherId, homeroom);
+            PlaceTextbook(school, pupilId, "Mathematics", ItemLocations.Bag);
+            var before = SkillOf(school, pupilId, "Mathematics");
+
+            LessonLearningSystem.Apply(school, 45);
+
+            Assert.True(SkillOf(school, pupilId, "Mathematics") > before);
+        }
+    }
+
+    [Theory]
+    [InlineData(ItemLocations.Locker)]
+    [InlineData(ItemLocations.Home)]
+    public void TextbookNotInBag_GainsHalf(string location)
+    {
+        var (school, homeroom, pupilId, teacherId) = StaffedMath();
+        using (school)
+        {
+            AdvanceTo(school, LessonStart);
+            SetPlace(school, pupilId, homeroom);
+            SetPlace(school, teacherId, homeroom);
+            PlaceTextbook(school, pupilId, "Mathematics", ItemLocations.Bag);
+            var start = SkillOf(school, pupilId, "Mathematics");
+            LessonLearningSystem.Apply(school, 45);
+            var bagGain = SkillOf(school, pupilId, "Mathematics") - start;
+
+            SetSkill(school, pupilId, "Mathematics", start);
+            PlaceTextbook(school, pupilId, "Mathematics", location);
+            LessonLearningSystem.Apply(school, 45);
+            var awayGain = SkillOf(school, pupilId, "Mathematics") - start;
+
+            Assert.True(bagGain > 0);
+            Assert.Equal(bagGain * 0.5f, awayGain, precision: 4);
+        }
+    }
+
+    [Fact]
+    public void OtherSubjectInBag_DoesNotCoverThisLesson()
+    {
+        var (school, homeroom, pupilId, teacherId) = StaffedMath();
+        using (school)
+        {
+            AdvanceTo(school, LessonStart);
+            SetPlace(school, pupilId, homeroom);
+            SetPlace(school, teacherId, homeroom);
+            PlaceTextbook(school, pupilId, "Mathematics", ItemLocations.Bag);
+            var start = SkillOf(school, pupilId, "Mathematics");
+            LessonLearningSystem.Apply(school, 45);
+            var mathGain = SkillOf(school, pupilId, "Mathematics") - start;
+
+            SetSkill(school, pupilId, "Mathematics", start);
+            PlaceTextbook(school, pupilId, "Literature", ItemLocations.Bag);
+            LessonLearningSystem.Apply(school, 45);
+            var otherGain = SkillOf(school, pupilId, "Mathematics") - start;
+
+            Assert.Equal(mathGain * 0.5f, otherGain, precision: 4);
+        }
+    }
+
+    [Fact]
+    public void NoTextbook_LogsOncePerSubject()
+    {
+        var (school, homeroom, pupilId, teacherId) = StaffedMath();
+        using (school)
+        {
+            AdvanceTo(school, LessonStart);
+            SetPlace(school, pupilId, homeroom);
+            SetPlace(school, teacherId, homeroom);
+            PlaceTextbook(school, pupilId, "Mathematics", ItemLocations.Home);
+
+            LessonLearningSystem.Apply(school, 5);
+            LessonLearningSystem.Apply(school, 5);
+
+            var rows = school.DayLog
+                .Where(row => row.PersonId == pupilId && row.Type == PersonLogTypes.LessonNoTextbook)
+                .ToArray();
+            Assert.Single(rows);
+            Assert.Equal("Mathematics", rows[0].ThingDef);
+            Assert.Equal("нет учебника: Математика", rows[0].Caption(school.Catalog!, "ru"));
+        }
+    }
+
     private static (School School, string Homeroom, string PupilId, string TeacherId) StaffedMath(
         string? teacherId = null)
     {
@@ -263,6 +353,25 @@ public class LessonTeacherPresentTests
         return (school, schoolClass.RoomId, pupil.Id, hiredId);
     }
 
+    private static void PlaceTextbook(School school, string personId, string subject, string location)
+    {
+        var person = school.Roster!.People.First(row => row.Id.Equals(personId, StringComparison.Ordinal));
+        if (person.Items is not IList<InventoryItem> items || items.IsReadOnly)
+        {
+            throw new InvalidOperationException($"Cannot mutate items for {personId}.");
+        }
+
+        for (var i = items.Count - 1; i >= 0; i--)
+        {
+            if (items[i].Subject is not null)
+            {
+                items.RemoveAt(i);
+            }
+        }
+
+        items.Add(new InventoryItem("Textbook", Color: null, Condition: 1f, location, subject));
+    }
+
     private static void AdvanceTo(School school, DateTime until)
     {
         while (school.Clock.Time < until)