Merge branch 'phase/51-warmth-lesson'

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

src/HSchool.Ai/LessonLearning.cs

@@ -3,9 +3,8 @@ using HSchool.Content;
 namespace HSchool.Ai;
 
 /// <summary>
-/// How much a lesson adds to one skill this step. Hungry learns worse; trait offsets and the
-/// teacher's subject skill scale the rate. The world stores the running total — this is just
-/// the number.
+/// 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.
 /// </summary>
 public static class LessonLearning
 {
@@ -54,13 +53,15 @@ public static class LessonLearning
         float hours,
         float hunger,
         int traitOffset,
-        float teacherSkill)
+        float teacherSkill,
+        float warmth = 1f)
     {
         ArgumentNullException.ThrowIfNull(skill);
         var delta = share
             * lessonSkillPerHour
             * hours
             * NeedFactor(hunger)
+            * NeedFactor(warmth)
             * TraitFactor(traitOffset)
             * TeacherFactor(teacherSkill);
         return Math.Clamp(current + delta, skill.Range.Min, skill.Range.Max);