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>

docs/phases/52-textbook-lesson.md

@@ -12,20 +12,20 @@
 
 ## Задачи
 
-- [ ] Рост урока полный, только если в **сумке** есть экземпляр с `subject` этого предмета
-- [ ] Шкафчик и дом не считаются: ученик в кабинете
-- [ ] Нет учебника — множитель `BehaviorDef.lessonNoTextbookFactor`, ваниль 0.5
-- [ ] Валидатор: число 0–1
-- [ ] Лог `lesson-no-textbook` один раз на предмет в сутки; `thingDef` — предмет
-- [ ] `docs/protocol.md` — тип лога
+- [x] Рост урока полный, только если в **сумке** есть экземпляр с `subject` этого предмета
+- [x] Шкафчик и дом не считаются: ученик в кабинете
+- [x] Нет учебника — множитель `BehaviorDef.lessonNoTextbookFactor`, ваниль 0.5
+- [x] Валидатор: число 0–1
+- [x] Лог `lesson-no-textbook` один раз на предмет в сутки; `thingDef` — предмет
+- [x] `docs/protocol.md` — тип лога
 
 ## Тесты, без которых фаза не закрыта
 
-- [ ] Учебник математики в сумке → полный рост (при учителе на месте)
-- [ ] Тот же учебник в шкафчике или дома → рост как с коэффициентом 0.5
-- [ ] Учебник другого предмета в сумке не закрывает этот урок
-- [ ] Одна строка лога за сутки на предмет, не по числу тиков
-- [ ] Пак без поля — 0.5, каталог не падает
+- [x] Учебник математики в сумке → полный рост (при учителе на месте)
+- [x] Тот же учебник в шкафчике или дома → рост как с коэффициентом 0.5
+- [x] Учебник другого предмета в сумке не закрывает этот урок
+- [x] Одна строка лога за сутки на предмет, не по числу тиков
+- [x] Пак без поля — 0.5, каталог не падает
 
 ## Критерий готовности
 

docs/protocol.md

@@ -417,7 +417,8 @@ arrive in one response.
 Row `type` values: `action-started`, `action-ended`, `apparel-replaced` (morning issue, when
 phase 34 appends it), `apparel-changed` (dressing, when phase 35 appends it),
 `lesson-no-teacher` (the assigned teacher was not standing in the lesson room),
-`lesson-cold` (warmth below the behaviour threshold during a lesson that otherwise taught).
+`lesson-cold` (warmth below the behaviour threshold during a lesson that otherwise taught),
+`lesson-no-textbook` (the bag had no textbook for that lesson; locker and home do not count).
 `thingDef` is the action, apparel or subject def the caption was built from.
 
 ```json

src/HSchool.Ai/LessonLearning.cs

@@ -1,10 +1,12 @@
 using HSchool.Content;
+using HSchool.People;
 
 namespace HSchool.Ai;
 
 /// <summary>
 /// How much a lesson adds to one skill this step. Hungry or cold learns worse; trait offsets and
-/// the teacher's subject skill scale the rate. Missing warmth is treated as 1.
+/// the teacher's subject skill scale the rate. Missing warmth is treated as 1. A missing textbook
+/// uses <see cref="BehaviorDef.LessonNoTextbookFactor"/>.
 /// </summary>
 public static class LessonLearning
 {
@@ -45,6 +47,28 @@ public static class LessonLearning
         return count == 0 ? 0f : total / count;
     }
 
+    /// <summary>
+    /// True when a bag instance carries this lesson's <see cref="InventoryItem.Subject"/>.
+    /// Locker and home do not count — the pupil is already in class.
+    /// </summary>
+    public static bool HasTextbookInBag(IReadOnlyList<InventoryItem> items, string subject)
+    {
+        ArgumentNullException.ThrowIfNull(items);
+        ArgumentException.ThrowIfNullOrWhiteSpace(subject);
+
+        foreach (var item in items)
+        {
+            if (item.Location.Equals(ItemLocations.Bag, StringComparison.Ordinal)
+                && item.Subject is not null
+                && item.Subject.Equals(subject, StringComparison.Ordinal))
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     public static float Gain(
         float current,
         SkillDef skill,
@@ -54,7 +78,8 @@ public static class LessonLearning
         float hunger,
         int traitOffset,
         float teacherSkill,
-        float warmth = 1f)
+        float warmth = 1f,
+        float textbookFactor = 1f)
     {
         ArgumentNullException.ThrowIfNull(skill);
         var delta = share
@@ -63,7 +88,8 @@ public static class LessonLearning
             * NeedFactor(hunger)
             * NeedFactor(warmth)
             * TraitFactor(traitOffset)
-            * TeacherFactor(teacherSkill);
+            * TeacherFactor(teacherSkill)
+            * textbookFactor;
         return Math.Clamp(current + delta, skill.Range.Min, skill.Range.Max);
     }
 }

src/HSchool.Content/PeopleDefValidator.cs

@@ -506,6 +506,11 @@ internal static class PeopleDefValidator
             throw new ContentLoadException($"BehaviorDef '{behavior.DefName}' lessonSkillPerHour cannot be negative.");
         }
 
+        if (behavior.LessonNoTextbookFactor is < 0f or > 1f)
+        {
+            throw new ContentLoadException($"BehaviorDef '{behavior.DefName}' lessonNoTextbookFactor must be 0–1.");
+        }
+
         if (behavior.SwitchMargin < 0f)
         {
             throw new ContentLoadException($"BehaviorDef '{behavior.DefName}' switchMargin cannot be negative.");

src/HSchool.Content/PeopleDefs.cs

@@ -274,6 +274,12 @@ public sealed class BehaviorDef : Def
     /// <summary>Skill points a lesson adds per game hour, before traits and need state.</summary>
     public float LessonSkillPerHour { get; init; }
 
+    /// <summary>
+    /// Multiplier when the bag has no textbook for this lesson. Locker and home do not count.
+    /// A pack without the field keeps vanilla half-gain so the catalog still loads.
+    /// </summary>
+    public float LessonNoTextbookFactor { get; init; } = 0.5f;
+
     /// <summary>Inclusive range of extra commute minutes rolled per person per day.</summary>
     public int CommuteSlackMin { get; init; }
 

src/HSchool.Server/mods/core/defs/behavior/rules.jsonc

@@ -4,6 +4,8 @@
   "needThreshold": 0.35,
   // Skill points a lesson adds per game hour, before traits and need state.
   "lessonSkillPerHour": 0.05,
+  // No textbook for this lesson in the bag (locker and home do not count).
+  "lessonNoTextbookFactor": 0.5,
   // Inclusive extra commute minutes. 0–6 matches the previous hardcoded roll so
   // the same seed still arrives at the same minute.
   "commuteSlackMin": 0,

src/HSchool.Server/mods/core/localizations/en.jsonc

@@ -206,5 +206,6 @@
   "ApparelChanged": "changed clothes: {0}",
   "LessonNoTeacher": "lesson without a teacher: {0}",
   "LessonCold": "too cold in class: {0}",
+  "LessonNoTextbook": "no textbook: {0}",
   "core": "Core",
 }

src/HSchool.Server/mods/core/localizations/ru.jsonc

@@ -206,5 +206,6 @@
   "ApparelChanged": "переоделся: {0}",
   "LessonNoTeacher": "урок без учителя: {0}",
   "LessonCold": "замёрз на уроке: {0}",
+  "LessonNoTextbook": "нет учебника: {0}",
   "core": "Базовая игра",
 }

src/HSchool.Simulation/LessonLearningSystem.cs

@@ -8,8 +8,9 @@ namespace HSchool.Simulation;
 
 /// <summary>
 /// Grows skills for people who are actually in the lesson: at the room, not walking, not off
-/// doing something else, and with the assigned teacher standing there. The formula lives in
-/// <see cref="HSchool.Ai.LessonLearning"/>.
+/// doing something else, and with the assigned teacher standing there. A pupil without today's
+/// textbook in the bag learns at <see cref="BehaviorDef.LessonNoTextbookFactor"/>. The formula
+/// lives in <see cref="HSchool.Ai.LessonLearning"/>.
 /// </summary>
 internal static class LessonLearningSystem
 {
@@ -90,6 +91,13 @@ internal static class LessonLearningSystem
                     school.TryLogLessonOnce(personId, PersonLogTypes.LessonCold, lesson.Subject);
                 }
 
+                var textbookFactor = 1f;
+                if (person.IsStudent && !LessonLearning.HasTextbookInBag(person.Items, lesson.Subject))
+                {
+                    textbookFactor = rules.LessonNoTextbookFactor;
+                    school.TryLogLessonOnce(personId, PersonLogTypes.LessonNoTextbook, lesson.Subject);
+                }
+
                 IReadOnlyDictionary<string, float> taught = teacherSkills.TryGetValue(lesson.TeacherId, out var found)
                     ? found
                     : new Dictionary<string, float>(StringComparer.Ordinal);
@@ -115,7 +123,8 @@ internal static class LessonLearningSystem
                         hunger,
                         TraitOffset(catalog, traits, share.Skill),
                         teacherSkill,
-                        warmth);
+                        warmth,
+                        textbookFactor);
                 }
             });
     }

src/HSchool.Simulation/PersonLog.cs

@@ -17,6 +17,7 @@ public static class PersonLogTypes
     public const string ApparelChanged = "apparel-changed";
     public const string LessonNoTeacher = "lesson-no-teacher";
     public const string LessonCold = "lesson-cold";
+    public const string LessonNoTextbook = "lesson-no-textbook";
 }
 
 /// <summary>
@@ -62,13 +63,16 @@ public sealed record PersonLogEvent(string PersonId, DateTime Time, string Type,
         }
 
         if (Type.Equals(PersonLogTypes.LessonNoTeacher, StringComparison.Ordinal)
-            || Type.Equals(PersonLogTypes.LessonCold, StringComparison.Ordinal))
+            || Type.Equals(PersonLogTypes.LessonCold, StringComparison.Ordinal)
+            || Type.Equals(PersonLogTypes.LessonNoTextbook, StringComparison.Ordinal))
         {
             var name = catalog.Subjects.TryGetValue(ThingDef, out var subject)
                 ? catalog.Label(locale, subject)
                 : ThingDef;
             var key = Type.Equals(PersonLogTypes.LessonCold, StringComparison.Ordinal)
                 ? "LessonCold"
+                : Type.Equals(PersonLogTypes.LessonNoTextbook, StringComparison.Ordinal)
+                    ? "LessonNoTextbook"
                     : "LessonNoTeacher";
             return string.Format(CultureInfo.InvariantCulture, catalog.Text(locale, key), name);
         }

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)