diff --git a/server/src/modules/leveling/lib/types.ts b/server/src/modules/leveling/lib/types.ts
new file mode 100644
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+++ b/server/src/modules/leveling/lib/types.ts
@@ -0,0 +1,88 @@
+/**
+ * Shared types for the Level-Up pure-function library.
+ * No runtime dependencies — types only.
+ */
+import type { AbilityAbbreviation } from './apply-attribute-boost';
+
+export type { AbilityAbbreviation };
+
+/** PF2e proficiency ranks (mirrors Prisma `Proficiency` enum). */
+export type Proficiency = 'UNTRAINED' | 'TRAINED' | 'EXPERT' | 'MASTER' | 'LEGENDARY';
+
+/** Numeric proficiency bonus per rank, for use in proficiencyBonus(rank, level) calculation. */
+export const PROFICIENCY_BASE_BONUS: Record<Proficiency, number> = {
+  UNTRAINED: 0,
+  TRAINED: 2,
+  EXPERT: 4,
+  MASTER: 6,
+  LEGENDARY: 8,
+};
+
+/** Discriminated union for prereq evaluation result. */
+export type EvalResult =
+  | { ok: true }
+  | { ok: false; reason: string }
+  | { unknown: true; raw: string };
+
+/** Ordered union of wizard step kinds (UI-SPEC + RESEARCH §Pattern 1). */
+export type StepKind =
+  | 'class-features'
+  | 'class-feature-choice'
+  | 'boost'
+  | 'skill-increase'
+  | 'feat-class'
+  | 'feat-skill'
+  | 'feat-general'
+  | 'feat-ancestry'
+  | 'feat-archetype'
+  | 'spellcaster'
+  | 'review';
+
+/** Snapshot a character's mechanical state for prereq evaluation and recompute. */
+export interface CharacterContext {
+  level: number;
+  className: string;
+  ancestryName: string;
+  heritageName?: string;
+  abilities: Record<AbilityAbbreviation, number>;
+  skills: Record<string, Proficiency>;
+  feats: Set<string>;
+}
+
+/** Output of recomputeDerivedStats — never includes hpCurrent (Pitfall #9). */
+export interface DerivedStats {
+  level: number;
+  hpMax: number;
+  ac: number;
+  classDc: number;
+  perception: number;
+  fortitude: number;
+  reflex: number;
+  will: number;
+}
+
+/** ClassProgression row shape — read-only input to recompute pipeline. */
+export interface ClassProgressionRow {
+  className: string;
+  level: number;
+  grants: string[];
+  proficiencyChanges: Partial<Record<'fortitude' | 'reflex' | 'will' | 'perception' | 'classDc' | 'ac', Proficiency>>;
+  spellSlotIncrement?: { tradition: string; spellLevel: number; count: number } | null;
+  cantripIncrement?: number | null;
+  repertoireIncrement?: number | null;
+  choiceType?: string | null;
+  choiceOptionsRef?: string | null;
+}
+
+/** Wizard choices subset — what the user picked across the wizard. */
+export interface WizardChoices {
+  boostTargets?: AbilityAbbreviation[];
+  skillIncrease?: { skillName: string; toRank: Proficiency };
+  featClassId?: string;
+  featSkillId?: string;
+  featGeneralId?: string;
+  featAncestryId?: string;
+  featArchetypeId?: string;
+  classFeatureChoices?: Record<string, string>;
+  spellcasterRepertoirePicks?: string[];
+}