Add manual CR assignment and difficulty breakdown panel

Implement issue #21: custom combatants can now have a challenge rating
assigned via a new breakdown panel, opened by tapping the difficulty
indicator. Bestiary-linked combatants show read-only CR with source name;
custom combatants get a CR picker with all standard 5e values. CR persists
across reloads and round-trips through JSON export/import.

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

apps/web/src/hooks/__tests__/use-difficulty-breakdown.test.tsx

@@ -0,0 +1,246 @@
+// @vitest-environment jsdom
+import type { Creature, CreatureId, PlayerCharacter } from "@initiative/domain";
+import { combatantId, creatureId, playerCharacterId } from "@initiative/domain";
+import { renderHook, waitFor } from "@testing-library/react";
+import type { ReactNode } from "react";
+import { beforeAll, describe, expect, it, vi } from "vitest";
+import { createTestAdapters } from "../../__tests__/adapters/in-memory-adapters.js";
+import {
+	buildCombatant,
+	buildCreature,
+	buildEncounter,
+} from "../../__tests__/factories/index.js";
+import { AllProviders } from "../../__tests__/test-providers.js";
+import { useDifficultyBreakdown } from "../use-difficulty-breakdown.js";
+
+beforeAll(() => {
+	Object.defineProperty(globalThis, "matchMedia", {
+		writable: true,
+		value: vi.fn().mockImplementation((query: string) => ({
+			matches: false,
+			media: query,
+			onchange: null,
+			addListener: vi.fn(),
+			removeListener: vi.fn(),
+			addEventListener: vi.fn(),
+			removeEventListener: vi.fn(),
+			dispatchEvent: vi.fn(),
+		})),
+	});
+});
+
+const pcId1 = playerCharacterId("pc-1");
+const goblinCreature = buildCreature({
+	id: creatureId("srd:goblin"),
+	name: "Goblin",
+	cr: "1/4",
+	source: "srd",
+	sourceDisplayName: "SRD",
+});
+
+function makeWrapper(options: {
+	encounter: ReturnType<typeof buildEncounter>;
+	playerCharacters?: PlayerCharacter[];
+	creatures?: Map<CreatureId, Creature>;
+}) {
+	const adapters = createTestAdapters({
+		encounter: options.encounter,
+		playerCharacters: options.playerCharacters ?? [],
+		creatures: options.creatures,
+	});
+	return ({ children }: { children: ReactNode }) => (
+		<AllProviders adapters={adapters}>{children}</AllProviders>
+	);
+}
+
+describe("useDifficultyBreakdown", () => {
+	it("returns null when no leveled PCs", () => {
+		const wrapper = makeWrapper({
+			encounter: buildEncounter({
+				combatants: [
+					buildCombatant({
+						id: combatantId("c-1"),
+						name: "Hero",
+						playerCharacterId: pcId1,
+					}),
+					buildCombatant({
+						id: combatantId("c-2"),
+						name: "Goblin",
+						creatureId: goblinCreature.id,
+					}),
+				],
+			}),
+			playerCharacters: [{ id: pcId1, name: "Hero", ac: 15, maxHp: 30 }],
+			creatures: new Map([[goblinCreature.id, goblinCreature]]),
+		});
+
+		const { result } = renderHook(() => useDifficultyBreakdown(), {
+			wrapper,
+		});
+		expect(result.current).toBeNull();
+	});
+
+	it("returns null when no monsters with CR", () => {
+		const wrapper = makeWrapper({
+			encounter: buildEncounter({
+				combatants: [
+					buildCombatant({
+						id: combatantId("c-1"),
+						name: "Hero",
+						playerCharacterId: pcId1,
+					}),
+					buildCombatant({
+						id: combatantId("c-2"),
+						name: "Custom",
+					}),
+				],
+			}),
+			playerCharacters: [
+				{ id: pcId1, name: "Hero", ac: 15, maxHp: 30, level: 5 },
+			],
+		});
+
+		const { result } = renderHook(() => useDifficultyBreakdown(), {
+			wrapper,
+		});
+		expect(result.current).toBeNull();
+	});
+
+	it("returns per-combatant entries with correct data", async () => {
+		const wrapper = makeWrapper({
+			encounter: buildEncounter({
+				combatants: [
+					buildCombatant({
+						id: combatantId("c-1"),
+						name: "Hero",
+						playerCharacterId: pcId1,
+					}),
+					buildCombatant({
+						id: combatantId("c-2"),
+						name: "Goblin",
+						creatureId: goblinCreature.id,
+					}),
+					buildCombatant({
+						id: combatantId("c-3"),
+						name: "Custom Thug",
+						cr: "2",
+					}),
+					buildCombatant({
+						id: combatantId("c-4"),
+						name: "Bandit",
+					}),
+				],
+			}),
+			playerCharacters: [
+				{ id: pcId1, name: "Hero", ac: 15, maxHp: 30, level: 5 },
+			],
+			creatures: new Map([[goblinCreature.id, goblinCreature]]),
+		});
+
+		const { result } = renderHook(() => useDifficultyBreakdown(), {
+			wrapper,
+		});
+
+		await waitFor(() => {
+			const breakdown = result.current;
+			expect(breakdown).not.toBeNull();
+			expect(breakdown?.pcCount).toBe(1);
+			// CR 1/4 = 50 + CR 2 = 450 → total 500
+			expect(breakdown?.totalMonsterXp).toBe(500);
+			expect(breakdown?.combatants).toHaveLength(3);
+
+			// Bestiary combatant
+			const goblin = breakdown?.combatants[0];
+			expect(goblin?.cr).toBe("1/4");
+			expect(goblin?.xp).toBe(50);
+			expect(goblin?.source).toBe("SRD");
+			expect(goblin?.editable).toBe(false);
+
+			// Custom with CR
+			const thug = breakdown?.combatants[1];
+			expect(thug?.cr).toBe("2");
+			expect(thug?.xp).toBe(450);
+			expect(thug?.source).toBeNull();
+			expect(thug?.editable).toBe(true);
+
+			// Custom without CR
+			const bandit = breakdown?.combatants[2];
+			expect(bandit?.cr).toBeNull();
+			expect(bandit?.xp).toBeNull();
+			expect(bandit?.source).toBeNull();
+			expect(bandit?.editable).toBe(true);
+		});
+	});
+
+	it("bestiary combatant with missing creature is non-editable with null CR", () => {
+		const missingCreatureId = creatureId("creature-missing");
+		const wrapper = makeWrapper({
+			encounter: buildEncounter({
+				combatants: [
+					buildCombatant({
+						id: combatantId("c-1"),
+						name: "Hero",
+						playerCharacterId: pcId1,
+					}),
+					buildCombatant({
+						id: combatantId("c-2"),
+						name: "Ghost",
+						creatureId: missingCreatureId,
+					}),
+					buildCombatant({
+						id: combatantId("c-3"),
+						name: "Thug",
+						cr: "1",
+					}),
+				],
+			}),
+			playerCharacters: [
+				{ id: pcId1, name: "Hero", ac: 15, maxHp: 30, level: 5 },
+			],
+		});
+
+		const { result } = renderHook(() => useDifficultyBreakdown(), {
+			wrapper,
+		});
+
+		// With no bestiary creatures loaded, the Ghost has null CR
+		const breakdown = result.current;
+		expect(breakdown).not.toBeNull();
+		const ghost = breakdown?.combatants[0];
+		expect(ghost?.cr).toBeNull();
+		expect(ghost?.xp).toBeNull();
+		expect(ghost?.editable).toBe(false);
+	});
+
+	it("excludes PC combatants from breakdown entries", async () => {
+		const wrapper = makeWrapper({
+			encounter: buildEncounter({
+				combatants: [
+					buildCombatant({
+						id: combatantId("c-1"),
+						name: "Hero",
+						playerCharacterId: pcId1,
+					}),
+					buildCombatant({
+						id: combatantId("c-2"),
+						name: "Goblin",
+						creatureId: goblinCreature.id,
+					}),
+				],
+			}),
+			playerCharacters: [
+				{ id: pcId1, name: "Hero", ac: 15, maxHp: 30, level: 1 },
+			],
+			creatures: new Map([[goblinCreature.id, goblinCreature]]),
+		});
+
+		const { result } = renderHook(() => useDifficultyBreakdown(), {
+			wrapper,
+		});
+
+		await waitFor(() => {
+			expect(result.current?.combatants).toHaveLength(1);
+			expect(result.current?.combatants[0].combatant.name).toBe("Goblin");
+		});
+	});
+});

apps/web/src/hooks/__tests__/use-difficulty-custom-cr.test.tsx

@@ -0,0 +1,173 @@
+// @vitest-environment jsdom
+import type { Creature, CreatureId, PlayerCharacter } from "@initiative/domain";
+import { combatantId, creatureId, playerCharacterId } from "@initiative/domain";
+import { renderHook, waitFor } from "@testing-library/react";
+import type { ReactNode } from "react";
+import { beforeAll, describe, expect, it, vi } from "vitest";
+import { createTestAdapters } from "../../__tests__/adapters/in-memory-adapters.js";
+import {
+	buildCombatant,
+	buildCreature,
+	buildEncounter,
+} from "../../__tests__/factories/index.js";
+import { AllProviders } from "../../__tests__/test-providers.js";
+import { useDifficulty } from "../use-difficulty.js";
+
+beforeAll(() => {
+	Object.defineProperty(globalThis, "matchMedia", {
+		writable: true,
+		value: vi.fn().mockImplementation((query: string) => ({
+			matches: false,
+			media: query,
+			onchange: null,
+			addListener: vi.fn(),
+			removeListener: vi.fn(),
+			addEventListener: vi.fn(),
+			removeEventListener: vi.fn(),
+			dispatchEvent: vi.fn(),
+		})),
+	});
+});
+
+const pcId1 = playerCharacterId("pc-1");
+const goblinCreature = buildCreature({
+	id: creatureId("srd:goblin"),
+	name: "Goblin",
+	cr: "1/4",
+});
+
+function makeWrapper(options: {
+	encounter: ReturnType<typeof buildEncounter>;
+	playerCharacters?: PlayerCharacter[];
+	creatures?: Map<CreatureId, Creature>;
+}) {
+	const adapters = createTestAdapters({
+		encounter: options.encounter,
+		playerCharacters: options.playerCharacters ?? [],
+		creatures: options.creatures,
+	});
+	return ({ children }: { children: ReactNode }) => (
+		<AllProviders adapters={adapters}>{children}</AllProviders>
+	);
+}
+
+describe("useDifficulty with custom combatant CRs", () => {
+	it("includes custom combatant with cr field in monster XP", () => {
+		const wrapper = makeWrapper({
+			encounter: buildEncounter({
+				combatants: [
+					buildCombatant({
+						id: combatantId("c-1"),
+						name: "Hero",
+						playerCharacterId: pcId1,
+					}),
+					buildCombatant({
+						id: combatantId("c-2"),
+						name: "Custom Thug",
+						cr: "2",
+					}),
+				],
+			}),
+			playerCharacters: [
+				{ id: pcId1, name: "Hero", ac: 15, maxHp: 30, level: 1 },
+			],
+		});
+
+		const { result } = renderHook(() => useDifficulty(), { wrapper });
+
+		expect(result.current).not.toBeNull();
+		expect(result.current?.totalMonsterXp).toBe(450);
+	});
+
+	it("uses bestiary CR when combatant has both creatureId and cr", async () => {
+		const wrapper = makeWrapper({
+			encounter: buildEncounter({
+				combatants: [
+					buildCombatant({
+						id: combatantId("c-1"),
+						name: "Hero",
+						playerCharacterId: pcId1,
+					}),
+					buildCombatant({
+						id: combatantId("c-2"),
+						name: "Goblin",
+						creatureId: goblinCreature.id,
+						cr: "5",
+					}),
+				],
+			}),
+			playerCharacters: [
+				{ id: pcId1, name: "Hero", ac: 15, maxHp: 30, level: 1 },
+			],
+			creatures: new Map([[goblinCreature.id, goblinCreature]]),
+		});
+
+		const { result } = renderHook(() => useDifficulty(), { wrapper });
+
+		await waitFor(() => {
+			expect(result.current).not.toBeNull();
+			// Should use bestiary CR 1/4 (50 XP), not the manual cr "5" (1800 XP)
+			expect(result.current?.totalMonsterXp).toBe(50);
+		});
+	});
+
+	it("mixes bestiary and custom-with-CR combatants correctly", async () => {
+		const wrapper = makeWrapper({
+			encounter: buildEncounter({
+				combatants: [
+					buildCombatant({
+						id: combatantId("c-1"),
+						name: "Hero",
+						playerCharacterId: pcId1,
+					}),
+					buildCombatant({
+						id: combatantId("c-2"),
+						name: "Goblin",
+						creatureId: goblinCreature.id,
+					}),
+					buildCombatant({
+						id: combatantId("c-3"),
+						name: "Custom",
+						cr: "1",
+					}),
+				],
+			}),
+			playerCharacters: [
+				{ id: pcId1, name: "Hero", ac: 15, maxHp: 30, level: 5 },
+			],
+			creatures: new Map([[goblinCreature.id, goblinCreature]]),
+		});
+
+		const { result } = renderHook(() => useDifficulty(), { wrapper });
+
+		await waitFor(() => {
+			expect(result.current).not.toBeNull();
+			// CR 1/4 = 50 XP, CR 1 = 200 XP → total 250
+			expect(result.current?.totalMonsterXp).toBe(250);
+		});
+	});
+
+	it("custom combatant without CR is still excluded", () => {
+		const wrapper = makeWrapper({
+			encounter: buildEncounter({
+				combatants: [
+					buildCombatant({
+						id: combatantId("c-1"),
+						name: "Hero",
+						playerCharacterId: pcId1,
+					}),
+					buildCombatant({
+						id: combatantId("c-2"),
+						name: "Custom Monster",
+					}),
+				],
+			}),
+			playerCharacters: [
+				{ id: pcId1, name: "Hero", ac: 15, maxHp: 30, level: 1 },
+			],
+		});
+
+		const { result } = renderHook(() => useDifficulty(), { wrapper });
+		expect(result.current).toBeNull();
+	});
+});

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

@@ -0,0 +1,140 @@
+import type {
+	Combatant,
+	CreatureId,
+	DifficultyTier,
+	PlayerCharacter,
+} from "@initiative/domain";
+import { calculateEncounterDifficulty, crToXp } from "@initiative/domain";
+import { useMemo } from "react";
+import { useBestiaryContext } from "../contexts/bestiary-context.js";
+import { useEncounterContext } from "../contexts/encounter-context.js";
+import { usePlayerCharactersContext } from "../contexts/player-characters-context.js";
+
+export interface BreakdownCombatant {
+	readonly combatant: Combatant;
+	readonly cr: string | null;
+	readonly xp: number | null;
+	readonly source: string | null;
+	readonly editable: boolean;
+}
+
+interface DifficultyBreakdown {
+	readonly tier: DifficultyTier;
+	readonly totalMonsterXp: number;
+	readonly partyBudget: {
+		readonly low: number;
+		readonly moderate: number;
+		readonly high: number;
+	};
+	readonly pcCount: number;
+	readonly combatants: readonly BreakdownCombatant[];
+}
+
+export function useDifficultyBreakdown(): DifficultyBreakdown | null {
+	const { encounter } = useEncounterContext();
+	const { characters } = usePlayerCharactersContext();
+	const { getCreature } = useBestiaryContext();
+
+	return useMemo(() => {
+		const partyLevels = derivePartyLevels(encounter.combatants, characters);
+		const { entries, crs } = classifyCombatants(
+			encounter.combatants,
+			getCreature,
+		);
+
+		if (partyLevels.length === 0 || crs.length === 0) {
+			return null;
+		}
+
+		const result = calculateEncounterDifficulty(partyLevels, crs);
+
+		return {
+			...result,
+			pcCount: partyLevels.length,
+			combatants: entries,
+		};
+	}, [encounter.combatants, characters, getCreature]);
+}
+
+function classifyBestiaryCombatant(
+	c: Combatant,
+	getCreature: (
+		id: CreatureId,
+	) => { cr: string; source: string; sourceDisplayName: string } | undefined,
+): { entry: BreakdownCombatant; cr: string | null } {
+	const creature = c.creatureId ? getCreature(c.creatureId) : undefined;
+	if (creature) {
+		return {
+			entry: {
+				combatant: c,
+				cr: creature.cr,
+				xp: crToXp(creature.cr),
+				source: creature.sourceDisplayName ?? creature.source,
+				editable: false,
+			},
+			cr: creature.cr,
+		};
+	}
+	return {
+		entry: {
+			combatant: c,
+			cr: null,
+			xp: null,
+			source: null,
+			editable: false,
+		},
+		cr: null,
+	};
+}
+
+function classifyCombatants(
+	combatants: readonly Combatant[],
+	getCreature: (
+		id: CreatureId,
+	) => { cr: string; source: string; sourceDisplayName: string } | undefined,
+): { entries: BreakdownCombatant[]; crs: string[] } {
+	const entries: BreakdownCombatant[] = [];
+	const crs: string[] = [];
+
+	for (const c of combatants) {
+		if (c.playerCharacterId) continue;
+
+		if (c.creatureId) {
+			const { entry, cr } = classifyBestiaryCombatant(c, getCreature);
+			entries.push(entry);
+			if (cr) crs.push(cr);
+		} else if (c.cr) {
+			crs.push(c.cr);
+			entries.push({
+				combatant: c,
+				cr: c.cr,
+				xp: crToXp(c.cr),
+				source: null,
+				editable: true,
+			});
+		} else {
+			entries.push({
+				combatant: c,
+				cr: null,
+				xp: null,
+				source: null,
+				editable: true,
+			});
+		}
+	}
+
+	return { entries, crs };
+}
+
+function derivePartyLevels(
+	combatants: readonly Combatant[],
+	characters: readonly PlayerCharacter[],
+): number[] {
+	const levels: number[] = [];
+	for (const c of combatants) {
+		if (!c.playerCharacterId) continue;
+		const pc = characters.find((p) => p.id === c.playerCharacterId);
+		if (pc?.level !== undefined) levels.push(pc.level);
+	}
+	return levels;
+}

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

@@ -29,9 +29,12 @@ function deriveMonsterCrs(
 ): string[] {
 	const crs: string[] = [];
 	for (const c of combatants) {
-		if (!c.creatureId) continue;
-		const creature = getCreature(c.creatureId);
-		if (creature) crs.push(creature.cr);
+		if (c.creatureId) {
+			const creature = getCreature(c.creatureId);
+			if (creature) crs.push(creature.cr);
+		} else if (c.cr) {
+			crs.push(c.cr);
+		}
 	}
 	return crs;
 }

apps/web/src/hooks/use-encounter.ts

@@ -9,6 +9,7 @@ import {
 	removeCombatantUseCase,
 	retreatTurnUseCase,
 	setAcUseCase,
+	setCrUseCase,
 	setHpUseCase,
 	setInitiativeUseCase,
 	setTempHpUseCase,
@@ -52,6 +53,7 @@ type EncounterAction =
 	| { type: "adjust-hp"; id: CombatantId; delta: number }
 	| { type: "set-temp-hp"; id: CombatantId; tempHp: number | undefined }
 	| { type: "set-ac"; id: CombatantId; value: number | undefined }
+	| { type: "set-cr"; id: CombatantId; value: string | undefined }
 	| {
 			type: "toggle-condition";
 			id: CombatantId;
@@ -318,6 +320,7 @@ function dispatchEncounterAction(
 		| { type: "adjust-hp" }
 		| { type: "set-temp-hp" }
 		| { type: "set-ac" }
+		| { type: "set-cr" }
 		| { type: "toggle-condition" }
 		| { type: "toggle-concentration" }
 	>,
@@ -358,6 +361,9 @@ function dispatchEncounterAction(
 		case "set-ac":
 			result = setAcUseCase(store, action.id, action.value);
 			break;
+		case "set-cr":
+			result = setCrUseCase(store, action.id, action.value);
+			break;
 		case "toggle-condition":
 			result = toggleConditionUseCase(store, action.id, action.conditionId);
 			break;
@@ -495,6 +501,11 @@ export function useEncounter() {
 				dispatch({ type: "set-ac", id, value }),
 			[],
 		),
+		setCr: useCallback(
+			(id: CombatantId, value: string | undefined) =>
+				dispatch({ type: "set-cr", id, value }),
+			[],
+		),
 		toggleCondition: useCallback(
 			(id: CombatantId, conditionId: ConditionId) =>
 				dispatch({ type: "toggle-condition", id, conditionId }),