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>

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>
@@ -62,14 +63,17 @@ 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"
-                : "LessonNoTeacher";
+                : Type.Equals(PersonLogTypes.LessonNoTextbook, StringComparison.Ordinal)
+                    ? "LessonNoTextbook"
+                    : "LessonNoTeacher";
             return string.Format(CultureInfo.InvariantCulture, catalog.Text(locale, key), name);
         }