Run 12: knowledge system, mortality, and the North's generational soul

SPEC §5 built: three skill domains (forage/woodcraft/masonry) that pay
off and grow by practice; proximity diffusion soul-calibrated by
absorption x teaching-drive; and mortality - the piece that makes
knowledge generational. Elders die (~150-230 days), everything unshared
dies with them, a youth comes of age near knowing nothing. North soul
(absorption 1.6, teaching 0.9) vs South (1.0, 0.3); East teaches no one.

Two findings: (1) headless soaks were contaminated by orphaned child
processes writing later runs' CSVs - fixed with StopAfterDays clean
self-terminate; (2) passive diffusion barely helped - the North's real
culture is the young seeking elders on purpose, so added deliberate
teacher-seeking and youths now cradle beside the wisest elder. North
now leads knowledge at every checkpoint, but a stable town approaches
the ceiling regardless, so teaching is a recovery advantage not an
equilibrium one. The crisis-recovery experiment is the real test, noted
in FINDINGS as next.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/Knowledge.cs

@@ -0,0 +1,47 @@
+using Godot;
+
+namespace WorldSim;
+
+/// <summary>Domains of practical knowledge (SPEC §5 — deliberately few).</summary>
+public enum KnowledgeDomain { Forage, Woodcraft, Masonry }
+
+/// <summary>
+/// What a person knows how to do (SPEC §5). Not an object in the world —
+/// it lives in people, spreads by proximity, grows by practice, and dies
+/// with its holder unless it was passed on. Every death is a small library
+/// burning; a teaching culture is a culture of copies.
+///
+/// Capacity is personal and randomized: some people can hold more than
+/// others, and what fills first is what they lived.
+/// </summary>
+public class Knowledge
+{
+    public const int DomainCount = 3;
+
+    /// <summary>0–1 per domain.</summary>
+    public float[] Skill = new float[DomainCount];
+
+    /// <summary>Total learning this mind can hold, across all domains.</summary>
+    public float Capacity = 1.5f;
+
+    public float Total => Skill[0] + Skill[1] + Skill[2];
+    public float Headroom => Mathf.Max(0f, Capacity - Total);
+
+    public float this[KnowledgeDomain d] => Skill[(int)d];
+
+    /// <summary>Learn, limited by personal capacity.</summary>
+    public void Gain(KnowledgeDomain d, float amount)
+    {
+        if (amount <= 0f || Headroom <= 0f) return;
+        float a = Mathf.Min(amount, Headroom);
+        Skill[(int)d] = Mathf.Clamp(Skill[(int)d] + a, 0f, 1f);
+    }
+
+    /// <summary>Which domain a material teaches and benefits from.</summary>
+    public static KnowledgeDomain DomainFor(MaterialKind kind) => kind switch
+    {
+        MaterialKind.Food => KnowledgeDomain.Forage,
+        MaterialKind.Wood => KnowledgeDomain.Woodcraft,
+        _                 => KnowledgeDomain.Masonry,   // stone, clay — builder's craft
+    };
+}