Sample outdoor weather from the climate preset so people can freeze and the clock can show it.

Protocol v8 adds tenths of a °C and precipitation to the clock frame; warmth drains from insulation versus place temperature.

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

src/HSchool.Simulation/WeatherSampler.cs

@@ -0,0 +1,53 @@
+using HSchool.Content;
+using HSchool.People;
+
+namespace HSchool.Simulation;
+
+/// <summary>
+/// Outdoor temperature and precipitation from a climate preset, the school seed, and the
+/// calendar. Same inputs always produce the same street. Not a tick accumulator — sample it
+/// when the clock label or warmth would move.
+/// </summary>
+public static class WeatherSampler
+{
+    private const int DaySalt = 0x57EA11;
+    private const int HourSalt = 0x57EA12;
+
+    public static OutdoorWeather Sample(ClimatePresetDef preset, int schoolSeed, DateTime time)
+    {
+        ArgumentNullException.ThrowIfNull(preset);
+
+        var utc = DateTime.SpecifyKind(time, DateTimeKind.Utc);
+        var month = utc.Month;
+        var norm = MonthNorm(preset, month);
+        var dayNumber = DateOnly.FromDateTime(utc).DayNumber;
+        var dayNoise = SignedUnit(Seed.Mix(schoolSeed, dayNumber, DaySalt)) * preset.DaySpread;
+        var hour = utc.Hour + utc.Minute / 60d + utc.Second / 3600d;
+        var diurnal = -Math.Cos((hour - 3d) / 24d * 2d * Math.PI) * preset.HourSpread;
+        var temperature = (float)(norm + dayNoise + diurnal);
+
+        var wet = Unit(Seed.Mix(schoolSeed, dayNumber * 24 + utc.Hour, HourSalt)) < preset.PrecipitationChance;
+        var precipitation = !wet
+            ? Precipitation.None
+            : temperature < 0f ? Precipitation.Snow : Precipitation.Rain;
+
+        return new OutdoorWeather(temperature, precipitation);
+    }
+
+    private static float MonthNorm(ClimatePresetDef preset, int month)
+    {
+        if (preset.MonthlyNorms.Count != 12)
+        {
+            return 0f;
+        }
+
+        return preset.MonthlyNorms[month - 1];
+    }
+
+    private static double Unit(int mixed)
+    {
+        return (uint)mixed / (double)uint.MaxValue;
+    }
+
+    private static double SignedUnit(int mixed) => Unit(mixed) * 2d - 1d;
+}