fix(inventory-go): add Prodigal Spirit Drinker effect; document dmgMod key substitution; test wand mastery fallback

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

go-services/inventory-go/od_test.go

@@ -23,6 +23,38 @@ func TestOD_Wand(t *testing.T) {
 	}
 }
 
+// Wand with an ACTIVE Prodigal Spirit Drinker (3735, change .15, bonus 0):
+// shown ElemVsMonsters 1.55 un-buffs to 1.55 − .15 = 1.40 → OD +22, same
+// underlying weapon as TestOD_Wand.
+func TestOD_WandActiveProdigalSpiritDrinker(t *testing.T) {
+	raw := map[string]any{
+		"ObjectClass":  31.0,
+		"IntValues":    map[string]any{"159": 34.0, "160": 385.0},
+		"DoubleValues": map[string]any{"152": 1.55, "167772169": 8.0},
+		"Spells":       []any{}, "ActiveSpells": []any{3735.0},
+	}
+	od, ok := computeOD(raw)
+	if !ok || !approx(od, 22.0) {
+		t.Fatalf("wand w/ active Prodigal SD OD = %v ok=%v, want +22", od, ok)
+	}
+}
+
+// Wand carrying a mastery value (353) with no matching wand table row: the
+// exact-match lookup on (34,5,0,385) misses, and the mastery-0 retry must hit
+// the (34,0,0,385) row → OD +22 as in TestOD_Wand.
+func TestOD_WandMasteryFallback(t *testing.T) {
+	raw := map[string]any{
+		"ObjectClass":  31.0,
+		"IntValues":    map[string]any{"159": 34.0, "353": 5.0, "160": 385.0},
+		"DoubleValues": map[string]any{"152": 1.40, "167772169": 8.0},
+		"Spells":       []any{}, "ActiveSpells": []any{},
+	}
+	od, ok := computeOD(raw)
+	if !ok || !approx(od, 22.0) {
+		t.Fatalf("wand mastery-fallback OD = %v ok=%v, want +22", od, ok)
+	}
+}
+
 // Non-loot (no workmanship) → no OD.
 func TestOD_NonLootNull(t *testing.T) {
 	raw := map[string]any{