feat(mosstank): cast buffs in retail's dependency order

MossTank was casting cheapest-first. That is a reasonable rule for surviving
a mana shortfall and a bad one for everything else, because AC's buff order is
not a preference -- each group raises the skill the next group is cast with:

  1. Creature Enchantment, and inside it:
       - the Creature Enchantment skill itself, which every remaining creature
         buff is then cast with;
       - Focus, then Willpower, then Endurance -- Focus and Self are the
         attributes the Item Enchantment and Life Magic skills derive from, so
         raising them raises the skill groups 2 and 3 are cast with;
       - the rest of the creature spells.
  2. Item Enchantment -- the banes and weapon auras.
  3. Life Magic last -- the protections and Armor Self.

Casting out of that order means casting at a lower skill than the character
could have had, which shows up as fizzles.

Grouping is by the spell's school rather than by name or category, so
protections land in group 3 because retail files them under Life Magic, not
because anything here says "protections go last".

Willpower is matched as "Self": retail's spell is named Willpower but its
description reads "Increases the caster's Self by 10 points", and MossTank
classifies from the description, so the name it matches is the one retail
actually writes. Verified against the spell table rather than assumed
(0x05A5 Willpower Self I).

Cheapest-first survives as the tiebreak inside a group, so a mana shortfall
still costs the cheapest of the last group instead of something the rest of
the pass depended on.

The two ordering tests were confirmed to fail when CastRank is neutralised --
the third guards the tiebreak and passes either way, by design.

Solution builds clean; 14,453 tests pass on the standard hermetic lane filter,
0 failures.

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

tests/AcDream.Plugins.MossTank.Tests/BuffPlanTests.cs

@@ -327,4 +327,110 @@ public class BuffPlanTests
             Array.Empty<PluginAttributeInfo>(), Array.Empty<PluginActiveEnchantment>(),
             Default));
     }
+
+    // ── Cast order: a dependency order, not a preference ─────────────────
+
+    private const uint ItemEnchantmentSkill = 32u;
+
+    /// <summary>
+    /// A spellbook holding one line of every group, with mana costs chosen to
+    /// fight the ordering: the buffs that must go FIRST are the most expensive,
+    /// so a plan that still sorted cheapest-first would come out backwards.
+    /// </summary>
+    private static List<BuffLine> OrderingSpellbook() => Lines(
+        // Creature Enchantment (school 31)
+        Spell(1, 101, 1, "Increases the caster's Creature Enchantment skill by 10 points.",
+            mana: 90, school: CreatureEnchantmentSkill),
+        Spell(2, 102, 1, "Increases the caster's Focus by 10 points.",
+            mana: 80, school: CreatureEnchantmentSkill),
+        Spell(3, 103, 1, "Increases the caster's Self by 10 points.",
+            mana: 70, school: CreatureEnchantmentSkill),
+        Spell(4, 104, 1, "Increases the caster's Endurance by 10 points.",
+            mana: 60, school: CreatureEnchantmentSkill),
+        Spell(5, 105, 1, "Increases the caster's Strength by 10 points.",
+            mana: 50, school: CreatureEnchantmentSkill),
+        Spell(6, 106, 1, "Increases the caster's Life Magic skill by 10 points.",
+            mana: 40, school: CreatureEnchantmentSkill),
+        // Item Enchantment (school 32)
+        Spell(7, 107, 1,
+            "Increases a shield or piece of armor's resistance to slashing damage by 10%. "
+            + "Target yourself to cast this spell on all of your equipped armor.",
+            mana: 30, school: ItemEnchantmentSkill),
+        Spell(8, 108, 1, "Increases a weapon's damage value by 2 points.",
+            mana: 20, school: ItemEnchantmentSkill),
+        // Life Magic (school 33)
+        Spell(9, 109, 1, "Reduces damage the caster takes from Fire by 9%.",
+            mana: 10, school: LifeMagicSkill));
+
+    private static List<PluginSpellInfo> OrderedPlan() =>
+        BuffPlan.Build(
+            OrderingSpellbook(),
+            new[]
+            {
+                Skill(CreatureEnchantmentSkill, "Creature Enchantment",
+                    PluginSkillTraining.Specialized),
+                Skill(ItemEnchantmentSkill, "Item Enchantment", PluginSkillTraining.Trained),
+                Skill(LifeMagicSkill, "Life Magic", PluginSkillTraining.Trained),
+            },
+            new[]
+            {
+                Attribute(0, "Strength"), Attribute(1, "Endurance"),
+                Attribute(4, "Focus"), Attribute(5, "Self"),
+            },
+            Array.Empty<PluginActiveEnchantment>(),
+            Default,
+            force: true);
+
+    [Fact]
+    public void CreatureSpellsCastFirst_ThenItem_ThenLifeLast()
+    {
+        List<PluginSpellInfo> plan = OrderedPlan();
+
+        // Every creature spell precedes every item spell, which precedes every
+        // life spell -- and the life protection is the CHEAPEST spell in the
+        // book, so this cannot be the cheapest-first sort passing by accident.
+        int lastCreature = plan.FindLastIndex(s => s.School == CreatureEnchantmentSkill);
+        int firstItem = plan.FindIndex(s => s.School == ItemEnchantmentSkill);
+        int lastItem = plan.FindLastIndex(s => s.School == ItemEnchantmentSkill);
+        int firstLife = plan.FindIndex(s => s.School == LifeMagicSkill);
+
+        Assert.True(lastCreature < firstItem,
+            "creature spells must all be cast before item spells");
+        Assert.True(lastItem < firstLife,
+            "item spells must all be cast before life spells");
+        Assert.Equal(plan.Count - 1, firstLife);   // the protection goes last
+    }
+
+    [Fact]
+    public void CreatureGroupLeadsWithMagicSkill_ThenFocus_Willpower_Endurance()
+    {
+        List<PluginSpellInfo> plan = OrderedPlan();
+
+        // Spell ids 1..4 are, in order: Creature Enchantment skill, Focus,
+        // Willpower (which retail words as "Self"), Endurance. Everything else
+        // creature follows them.
+        Assert.Equal(new uint[] { 1, 2, 3, 4 }, plan.Take(4).Select(s => s.SpellId));
+
+        // ...and "the rest of the creature spells" really are after, not mixed in.
+        Assert.Equal(
+            new uint[] { 5, 6 },
+            plan.Skip(4)
+                .Where(s => s.School == CreatureEnchantmentSkill)
+                .Select(s => s.SpellId)
+                .OrderBy(id => id));
+    }
+
+    [Fact]
+    public void WithinOneGroupTheCheapestStillCastsFirst()
+    {
+        // Ordering outranks cost, but among equals cost still decides -- if mana
+        // runs out mid-pass the casualties should be the priciest of the group.
+        List<PluginSpellInfo> plan = OrderedPlan();
+        List<PluginSpellInfo> item =
+            plan.Where(s => s.School == ItemEnchantmentSkill).ToList();
+
+        Assert.Equal(2, item.Count);
+        Assert.True(item[0].ManaCost <= item[1].ManaCost);
+        Assert.Equal(8u, item[0].SpellId);   // the 20-mana aura before the 30-mana bane
+    }
 }