Add Recall Knowledge DC and skill to PF2e stat blocks

Display Recall Knowledge line below trait tags showing DC (from level
via standard DC-by-level table, adjusted for rarity) and associated
skill derived from creature type trait. Omitted for D&D creatures and
creatures with no recognized type trait.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/domain/src/recall-knowledge.ts

@@ -0,0 +1,118 @@
+/**
+ * PF2e Recall Knowledge DC calculation and type-to-skill mapping.
+ *
+ * DC is derived from creature level using the standard DC-by-level table
+ * (Player Core / GM Core), adjusted for rarity.
+ */
+
+/** Standard DC-by-level table from PF2e GM Core. Index = level + 1 (level -1 → index 0). */
+const DC_BY_LEVEL: readonly number[] = [
+	13, // level -1
+	14, // level 0
+	15, // level 1
+	16, // level 2
+	18, // level 3
+	19, // level 4
+	20, // level 5
+	22, // level 6
+	23, // level 7
+	24, // level 8
+	26, // level 9
+	27, // level 10
+	28, // level 11
+	30, // level 12
+	31, // level 13
+	32, // level 14
+	34, // level 15
+	35, // level 16
+	36, // level 17
+	38, // level 18
+	39, // level 19
+	40, // level 20
+	42, // level 21
+	44, // level 22
+	46, // level 23
+	48, // level 24
+	50, // level 25
+];
+
+const RARITY_ADJUSTMENT: Readonly<Record<string, number>> = {
+	uncommon: 2,
+	rare: 5,
+	unique: 10,
+};
+
+/**
+ * Mapping from PF2e creature type traits to the skill(s) used for
+ * Recall Knowledge. Types that map to multiple skills list all of them.
+ */
+const TYPE_TO_SKILLS: Readonly<Record<string, readonly string[]>> = {
+	aberration: ["Occultism"],
+	animal: ["Nature"],
+	astral: ["Occultism"],
+	beast: ["Arcana", "Nature"],
+	celestial: ["Religion"],
+	construct: ["Arcana", "Crafting"],
+	dragon: ["Arcana"],
+	dream: ["Occultism"],
+	elemental: ["Arcana", "Nature"],
+	ethereal: ["Occultism"],
+	fey: ["Nature"],
+	fiend: ["Religion"],
+	fungus: ["Nature"],
+	giant: ["Society"],
+	humanoid: ["Society"],
+	monitor: ["Religion"],
+	ooze: ["Occultism"],
+	plant: ["Nature"],
+	undead: ["Religion"],
+};
+
+export interface RecallKnowledge {
+	readonly dc: number;
+	readonly type: string;
+	readonly skills: readonly string[];
+}
+
+/**
+ * Calculate Recall Knowledge DC, type, and skill(s) for a PF2e creature.
+ *
+ * Returns `null` when no recognized type trait is found in the creature's
+ * traits array, indicating the Recall Knowledge line should be omitted.
+ */
+export function recallKnowledge(
+	level: number,
+	traits: readonly string[],
+): RecallKnowledge | null {
+	// Find the first type trait that maps to a skill
+	let matchedType: string | undefined;
+	let skills: readonly string[] | undefined;
+
+	for (const trait of traits) {
+		const lower = trait.toLowerCase();
+		const mapped = TYPE_TO_SKILLS[lower];
+		if (mapped) {
+			matchedType = trait;
+			skills = mapped;
+			break;
+		}
+	}
+
+	if (!matchedType || !skills) return null;
+
+	// Calculate DC from level
+	const clampedIndex = Math.max(0, Math.min(level + 1, DC_BY_LEVEL.length - 1));
+	let dc = DC_BY_LEVEL[clampedIndex];
+
+	// Apply rarity adjustment (rarity traits are included in the traits array
+	// for non-common creatures by the normalization pipeline)
+	for (const trait of traits) {
+		const adjustment = RARITY_ADJUSTMENT[trait.toLowerCase()];
+		if (adjustment) {
+			dc += adjustment;
+			break;
+		}
+	}
+
+	return { dc, type: matchedType, skills };
+}