D&D: import Open5e SRD magic items as a vendored reference registry

fetch/gen magicitems subcommands vendor data/open5e/magicitems.json (237
SRD items) and classify them into a generated registry. magic_items.go
holds the MagicItem struct + Kind enum + an init-time overlay merge where
a hand-authored entry wins on ID collision, mirroring the spell and
bestiary imports. Not yet wired into zone loot or the shop — that
integration is a deliberate follow-up.

internal/plugin/magic_items_test.go

@@ -0,0 +1,72 @@
+package plugin
+
+import "testing"
+
+// TestMagicItemRegistryPopulated guards the generated SRD dump against an empty
+// or structurally broken regeneration.
+func TestMagicItemRegistryPopulated(t *testing.T) {
+	if len(magicItemRegistry) < 200 {
+		t.Fatalf("magic item registry too small: got %d, want >= 200", len(magicItemRegistry))
+	}
+	for id, mi := range magicItemRegistry {
+		if mi.ID != id {
+			t.Errorf("registry key %q != item ID %q", id, mi.ID)
+		}
+		if mi.Name == "" {
+			t.Errorf("%s: empty Name", id)
+		}
+		if mi.Kind == "" {
+			t.Errorf("%s: empty Kind", id)
+		}
+		if mi.Rarity == "" {
+			t.Errorf("%s: empty Rarity", id)
+		}
+		if mi.Value <= 0 {
+			t.Errorf("%s: non-positive Value %d", id, mi.Value)
+		}
+	}
+}
+
+// TestMagicItemSpotCheck pins a few classifier outputs so a regeneration that
+// changes the heuristics gets caught.
+func TestMagicItemSpotCheck(t *testing.T) {
+	armor, ok := magicItemRegistry["adamantine_armor"]
+	if !ok {
+		t.Fatal("adamantine_armor missing from registry")
+	}
+	if armor.Kind != MagicItemArmor || armor.Rarity != RarityUncommon ||
+		armor.Slot != DnDSlotChest || armor.Attunement {
+		t.Errorf("adamantine_armor classified wrong: %+v", armor)
+	}
+
+	amulet, ok := magicItemRegistry["amulet_of_health"]
+	if !ok {
+		t.Fatal("amulet_of_health missing from registry")
+	}
+	if amulet.Kind != MagicItemWondrous || amulet.Rarity != RarityRare ||
+		amulet.Slot != DnDSlotAmulet || !amulet.Attunement {
+		t.Errorf("amulet_of_health classified wrong: %+v", amulet)
+	}
+}
+
+// TestMagicItemOverlayWins verifies the hand-authored overlay layers on top of
+// the generated dump and wins on ID collision. It exercises the merge with a
+// throwaway item so the assertion holds even while magicItemOverlay is empty.
+func TestMagicItemOverlayWins(t *testing.T) {
+	saved := magicItemOverlay
+	defer func() {
+		magicItemOverlay = saved
+		magicItemRegistry = buildMagicItemRegistry()
+	}()
+
+	magicItemOverlay = []MagicItem{
+		{ID: "adamantine_armor", Name: "Hand-Tuned Plate", Kind: MagicItemArmor,
+			Rarity: RarityLegendary, Value: 9999},
+	}
+	magicItemRegistry = buildMagicItemRegistry()
+
+	got := magicItemRegistry["adamantine_armor"]
+	if got.Name != "Hand-Tuned Plate" || got.Rarity != RarityLegendary {
+		t.Errorf("overlay did not win on ID collision: %+v", got)
+	}
+}