feat: replacement effects in Module 4 (Armor absorption, Bolf Ramshield redirect)

Applying a Damage to one target now runs DAMAGE_STEPS = [redirect, armor]
first. A damageRedirect aura (Bolf Ramshield, fetched from the wiki) sends
damage meant for its owner's hero to the oldest such minion; Armor absorbs
damage to a hero before Health, logged as the new ArmorLost{player, amount}
just before a full-amount Damaged. Four new Module 4 tests; propagated to the
references of Modules 4-10 in both tracks; card schema, catalog, card JSON,
harness.md, Lessons 2, 4 and 5 updated.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

course/06-parser/reference/ts/src/engine/aura.ts

@@ -1,4 +1,5 @@
-// Auras, and the one routine that applies trigger multipliers.
+// Auras, the one routine that applies trigger multipliers, and the lookup for
+// damage redirects.
 //
 // An aura is data on a card: a continuous effect its minion has while in play.
 // The engine never asks "is that card on the board?" in the middle of resolving
@@ -12,17 +13,26 @@
 // Summoning a minion also runs an Aura Update.
 
 import type { TriggerOn } from "./card";
-import type { PlayerId, World } from "./world";
+import type { EntityId, PlayerId, World } from "./world";
 
 /** Aura Update (Other): replace the snapshot with the auras of every minion now in play. */
 export function auraUpdateOther(world: World): void {
   world.setActiveAuras(
     world.minionsInPlay().flatMap((id) =>
-      world.card(world.cardName(id)).auras.map((aura) => ({ owner: world.ownerOf(id), aura })),
+      world.card(world.cardName(id)).auras.map((aura) => ({ owner: world.ownerOf(id), source: id, aura })),
     ),
   );
 }
 
+/**
+ * The minion that takes damage meant for `player`'s hero, if a redirect is in force:
+ * the oldest (order of play) of `player`'s minions with a `damageRedirect` aura in the
+ * snapshot. The snapshot lists minions oldest first, so that is the first one found.
+ */
+export function redirectFor(world: World, player: PlayerId): EntityId | undefined {
+  return world.activeAuras().find((a) => a.aura.type === "damageRedirect" && a.owner === player)?.source;
+}
+
 /**
  * How many times a trigger listening for `on`, on a minion `owner` controls, activates
  * when it resolves. Reads the snapshot from the last Aura Update. With no multiplier in
@@ -32,9 +42,10 @@ export function auraUpdateOther(world: World): void {
 export function activations(world: World, owner: PlayerId, on: TriggerOn): number {
   let max = 1;
   let extra = 0;
-  for (const active of world.activeAuras()) {
-    const { trigger, times, stacking } = active.aura;
-    if (active.owner !== owner || trigger !== on) continue;
+  for (const { owner: auraOwner, aura } of world.activeAuras()) {
+    if (aura.type !== "triggerMultiplier") continue;
+    const { trigger, times, stacking } = aura;
+    if (auraOwner !== owner || trigger !== on) continue;
     if (stacking === "max") max = Math.max(max, times);
     else extra += times - 1;
   }