Add PF2e encounter difficulty calculation with 5-tier budget system

Implements PF2e encounter difficulty alongside the existing D&D system.
PF2e uses creature level vs party level to derive XP, compares against
5-tier budgets (Trivial/Low/Moderate/Severe/Extreme), and adjusts
thresholds for party size. The indicator shows 4 bars in PF2e mode.

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

apps/web/src/hooks/use-difficulty-breakdown.ts

@@ -1,11 +1,17 @@
 import type {
+	AnyCreature,
 	Combatant,
 	CreatureId,
 	DifficultyThreshold,
 	DifficultyTier,
 	PlayerCharacter,
 } from "@initiative/domain";
-import { calculateEncounterDifficulty, crToXp } from "@initiative/domain";
+import {
+	calculateEncounterDifficulty,
+	crToXp,
+	derivePartyLevel,
+	pf2eCreatureXp,
+} from "@initiative/domain";
 import { useMemo } from "react";
 import { useBestiaryContext } from "../contexts/bestiary-context.js";
 import { useEncounterContext } from "../contexts/encounter-context.js";
@@ -21,6 +27,10 @@ export interface BreakdownCombatant {
 	readonly editable: boolean;
 	readonly side: "party" | "enemy";
 	readonly level: number | undefined;
+	/** PF2e only: the creature's level from bestiary data. */
+	readonly creatureLevel: number | undefined;
+	/** PF2e only: creature level minus party level. */
+	readonly levelDifference: number | undefined;
 }
 
 interface DifficultyBreakdown {
@@ -30,6 +40,7 @@ interface DifficultyBreakdown {
 	readonly encounterMultiplier: number | undefined;
 	readonly adjustedXp: number | undefined;
 	readonly partySizeAdjusted: boolean | undefined;
+	readonly partyLevel: number | undefined;
 	readonly pcCount: number;
 	readonly partyCombatants: readonly BreakdownCombatant[];
 	readonly enemyCombatants: readonly BreakdownCombatant[];
@@ -48,9 +59,16 @@ export function useDifficultyBreakdown(): DifficultyBreakdown | null {
 		const hasPartyLevel = descriptors.some(
 			(d) => d.side === "party" && d.level !== undefined,
 		);
-		const hasCr = descriptors.some((d) => d.cr !== undefined);
 
-		if (!hasPartyLevel || !hasCr) return null;
+		if (edition === "pf2e") {
+			const hasCreatureLevel = descriptors.some(
+				(d) => d.creatureLevel !== undefined,
+			);
+			if (!hasPartyLevel || !hasCreatureLevel) return null;
+		} else {
+			const hasCr = descriptors.some((d) => d.cr !== undefined);
+			if (!hasPartyLevel || !hasCr) return null;
+		}
 
 		const result = calculateEncounterDifficulty(descriptors, edition);
 
@@ -65,6 +83,7 @@ export function useDifficultyBreakdown(): DifficultyBreakdown | null {
 
 type CreatureInfo = {
 	cr?: string;
+	creatureLevel?: number;
 	source: string;
 	sourceDisplayName: string;
 };
@@ -74,6 +93,7 @@ function buildBreakdownEntry(
 	side: "party" | "enemy",
 	level: number | undefined,
 	creature: CreatureInfo | undefined,
+	partyLevel: number | undefined,
 ): BreakdownCombatant {
 	if (c.playerCharacterId) {
 		return {
@@ -84,6 +104,29 @@ function buildBreakdownEntry(
 			editable: false,
 			side,
 			level,
+			creatureLevel: undefined,
+			levelDifference: undefined,
+		};
+	}
+	if (creature && creature.creatureLevel !== undefined) {
+		const levelDiff =
+			partyLevel === undefined
+				? undefined
+				: creature.creatureLevel - partyLevel;
+		const xp =
+			partyLevel === undefined
+				? null
+				: pf2eCreatureXp(creature.creatureLevel, partyLevel);
+		return {
+			combatant: c,
+			cr: null,
+			xp,
+			source: creature.sourceDisplayName ?? creature.source,
+			editable: false,
+			side,
+			level: undefined,
+			creatureLevel: creature.creatureLevel,
+			levelDifference: levelDiff,
 		};
 	}
 	if (creature) {
@@ -96,6 +139,8 @@ function buildBreakdownEntry(
 			editable: false,
 			side,
 			level: undefined,
+			creatureLevel: undefined,
+			levelDifference: undefined,
 		};
 	}
 	if (c.cr) {
@@ -107,6 +152,8 @@ function buildBreakdownEntry(
 			editable: true,
 			side,
 			level: undefined,
+			creatureLevel: undefined,
+			levelDifference: undefined,
 		};
 	}
 	return {
@@ -117,6 +164,8 @@ function buildBreakdownEntry(
 		editable: !c.creatureId,
 		side,
 		level: undefined,
+		creatureLevel: undefined,
+		levelDifference: undefined,
 	};
 }
 
@@ -128,41 +177,91 @@ function resolveLevel(
 	return characters.find((p) => p.id === c.playerCharacterId)?.level;
 }
 
-function resolveCr(
+function resolveCreatureInfo(
 	c: Combatant,
-	getCreature: (id: CreatureId) => CreatureInfo | undefined,
-): { cr: string | null; creature: CreatureInfo | undefined } {
-	const creature = c.creatureId ? getCreature(c.creatureId) : undefined;
-	const cr = creature?.cr ?? c.cr ?? null;
-	return { cr, creature };
+	getCreature: (id: CreatureId) => AnyCreature | undefined,
+): {
+	cr: string | null;
+	creatureLevel: number | undefined;
+	creature: CreatureInfo | undefined;
+} {
+	const rawCreature = c.creatureId ? getCreature(c.creatureId) : undefined;
+	if (!rawCreature) {
+		return {
+			cr: c.cr ?? null,
+			creatureLevel: undefined,
+			creature: undefined,
+		};
+	}
+	if ("system" in rawCreature && rawCreature.system === "pf2e") {
+		return {
+			cr: null,
+			creatureLevel: rawCreature.level,
+			creature: {
+				creatureLevel: rawCreature.level,
+				source: rawCreature.source,
+				sourceDisplayName: rawCreature.sourceDisplayName,
+			},
+		};
+	}
+	const cr = "cr" in rawCreature ? rawCreature.cr : undefined;
+	return {
+		cr: cr ?? c.cr ?? null,
+		creatureLevel: undefined,
+		creature: {
+			cr,
+			source: rawCreature.source,
+			sourceDisplayName: rawCreature.sourceDisplayName,
+		},
+	};
+}
+
+function collectPartyLevel(
+	combatants: readonly Combatant[],
+	characters: readonly PlayerCharacter[],
+): number | undefined {
+	const partyLevels: number[] = [];
+	for (const c of combatants) {
+		if (resolveSide(c) !== "party") continue;
+		const level = resolveLevel(c, characters);
+		if (level !== undefined) partyLevels.push(level);
+	}
+	return partyLevels.length > 0 ? derivePartyLevel(partyLevels) : undefined;
 }
 
 function classifyCombatants(
 	combatants: readonly Combatant[],
 	characters: readonly PlayerCharacter[],
-	getCreature: (id: CreatureId) => CreatureInfo | undefined,
+	getCreature: (id: CreatureId) => AnyCreature | undefined,
 ) {
 	const partyCombatants: BreakdownCombatant[] = [];
 	const enemyCombatants: BreakdownCombatant[] = [];
 	const descriptors: {
 		level?: number;
 		cr?: string;
+		creatureLevel?: number;
 		side: "party" | "enemy";
 	}[] = [];
 	let pcCount = 0;
+	const partyLevel = collectPartyLevel(combatants, characters);
 
 	for (const c of combatants) {
 		const side = resolveSide(c);
 		const level = resolveLevel(c, characters);
 		if (level !== undefined) pcCount++;
 
-		const { cr, creature } = resolveCr(c, getCreature);
+		const { cr, creatureLevel, creature } = resolveCreatureInfo(c, getCreature);
 
-		if (level !== undefined || cr != null) {
-			descriptors.push({ level, cr: cr ?? undefined, side });
+		if (level !== undefined || cr != null || creatureLevel !== undefined) {
+			descriptors.push({
+				level,
+				cr: cr ?? undefined,
+				creatureLevel,
+				side,
+			});
 		}
 
-		const entry = buildBreakdownEntry(c, side, level, creature);
+		const entry = buildBreakdownEntry(c, side, level, creature, partyLevel);
 		const target = side === "party" ? partyCombatants : enemyCombatants;
 		target.push(entry);
 	}