diff --git a/src/engine/types.ts b/src/engine/types.ts
new file mode 100644
index 0000000..ad20157
--- /dev/null
+++ b/src/engine/types.ts
@@ -0,0 +1,84 @@
+// Engine type definitions. No runtime code — these shapes are the contract
+// between the world data, the engine, and the UI.
+
+export type RoomId = string
+export type ItemId = string
+export type EncounterId = string
+export type Direction = 'n' | 's' | 'e' | 'w' | 'u' | 'd'
+
+export type Verb =
+  | 'go' | 'look' | 'examine' | 'take' | 'drop' | 'use' | 'open' | 'close'
+  | 'read' | 'light' | 'extinguish' | 'attack' | 'inventory' | 'wait'
+  | 'hold' | 'push' | 'pull'
+
+export type MetaVerb = 'restart' | 'undo' | 'hint' | 'save' | 'quit' | 'theme'
+
+export interface NounRef {
+  /** Canonical noun (matches an ItemId, EncounterId, or a directional/world noun). */
+  canonical: string
+  /** The raw token(s) the player typed, for narration. */
+  raw: string
+}
+
+export type ParsedCommand =
+  | { kind: 'verb-only'; verb: Verb | 'look' | 'inventory' | 'wait' }
+  | { kind: 'verb-target'; verb: Verb; target: NounRef }
+  | { kind: 'verb-target-prep'; verb: Verb; target: NounRef; preposition: string; indirect: NounRef }
+  | { kind: 'go'; direction: Direction }
+  | { kind: 'meta'; verb: MetaVerb }
+  | { kind: 'disambiguation'; chosen: string }
+  | { kind: 'unknown'; raw: string; reason: 'unknown-verb' | 'unknown-noun' | 'malformed' }
+
+export type ResolveLevel = 'steady' | 'shaken' | 'reeling' | 'returning'
+export type Theme = 'amber' | 'ansi'
+
+export interface ItemInstance {
+  id: ItemId
+  /** Per-instance state: lit/unlit, broken/whole, etc. */
+  state: Record<string, string | boolean | number>
+}
+
+export type EncounterPhase = string  // phase names are encounter-specific
+
+export interface TranscriptLine {
+  kind: 'narration' | 'player' | 'system'
+  text: string
+}
+
+export interface PendingDisambiguation {
+  verb: Verb
+  candidates: string[]   // canonical noun ids the player must choose between
+  prompt: string
+}
+
+export interface GameState {
+  schemaVersion: number
+  location: RoomId
+  inventory: ItemInstance[]
+  /** Per-room state: visited, items dropped, descriptive flags. */
+  roomState: Record<RoomId, Record<string, string | boolean | number>>
+  /** Story-wide flags (e.g. 'gateOpened', 'mirrorTarnished'). */
+  flags: Record<string, string | boolean | number>
+  resolveLevel: ResolveLevel
+  /** Active encounter phase by encounter id, or null if no encounter is mid-flight. */
+  encounterState: Record<EncounterId, EncounterPhase>
+  /** Last referenced noun, for pronoun resolution. */
+  lastNoun: NounRef | null
+  /** Pending multi-word disambiguation, set when the parser cannot decide. */
+  pendingDisambiguation: PendingDisambiguation | null
+  /** Capped at 200 entries; older entries are dropped on append. */
+  transcript: TranscriptLine[]
+  theme: Theme
+  /** Set true when the player has reached an ending. UI shows ending screen. */
+  endedWith: 'true' | 'wrong' | 'bad' | null
+}
+
+export interface DispatchResult {
+  state: GameState
+  /** Lines to append to the transcript (already added to state.transcript). */
+  appended: TranscriptLine[]
+}
+
+export const SCHEMA_VERSION = 1
+export const TRANSCRIPT_CAP = 200
+export const RESOLVE_LEVELS: ResolveLevel[] = ['steady', 'shaken', 'reeling', 'returning']
diff --git a/src/world/types.ts b/src/world/types.ts
new file mode 100644
index 0000000..a1449b5
--- /dev/null
+++ b/src/world/types.ts
@@ -0,0 +1,90 @@
+// World data type definitions. World modules export plain data conforming to
+// these shapes; the engine reads but never mutates them.
+
+import type { RoomId, ItemId, EncounterId, Direction, Verb, EncounterPhase } from '../engine/types'
+
+export interface RoomDescriptions {
+  /** Shown the first time the player enters this room. */
+  firstVisit: string
+  /** Shown on subsequent entries. */
+  revisit: string
+  /** Shown when the player types `look` (richer detail). */
+  examined: string
+}
+
+export interface Room {
+  id: RoomId
+  title: string                       // e.g. "[ Foyer ]"
+  descriptions: RoomDescriptions
+  /** Direction → destination room id. Locked exits are listed in `lockedExits`. */
+  exits: Partial<Record<Direction, RoomId>>
+  /** Direction → unlock condition (item id or flag name). */
+  lockedExits?: Partial<Record<Direction, { requires: ItemId | string; lockedNarration: string }>>
+  /** Items that start in this room. Items the player drops are tracked in roomState. */
+  items: ItemId[]
+  /** Encounter that triggers when this room is entered, or null. */
+  encounter?: EncounterId
+  /** Optional "safe" flag: entering a safe room regenerates one resolve step. */
+  safe?: boolean
+}
+
+export interface Item {
+  id: ItemId
+  /** Canonical name and any aliases for the parser. */
+  names: string[]
+  /** Short description shown in inventory. */
+  short: string
+  /** Long description shown when examined. */
+  long: string
+  /** Initial per-instance state (e.g. `{ lit: false }`). */
+  initialState: Record<string, string | boolean | number>
+  /** True if the player can pick it up. */
+  takeable: boolean
+}
+
+export interface EncounterPhaseDef {
+  /** Description shown each turn while in this phase. */
+  description: string
+  transitions: EncounterTransition[]
+}
+
+export interface EncounterTransition {
+  verb: Verb
+  /** Required target noun id, or '*' for any target, or undefined for verb-only. */
+  target?: ItemId | EncounterId | '*'
+  /** Required item id in inventory (and optional state predicate). */
+  requires?: { item: ItemId; state?: Record<string, string | boolean | number> }
+  /** Phase to transition to, or 'resolved' / 'failed'. */
+  to: EncounterPhase | 'resolved' | 'failed'
+  /** Narration on this transition. */
+  narration: string
+  /** Resolve cost for the player on this transition (0–2). */
+  resolveCost?: 0 | 1 | 2
+}
+
+export interface EncounterDef {
+  id: EncounterId
+  startsIn: RoomId
+  initialPhase: EncounterPhase
+  phases: Record<EncounterPhase, EncounterPhaseDef>
+  /** Effects on resolution (set flags, unlock exits). */
+  onResolved?: { setFlags?: Record<string, string | boolean | number>; unlockExits?: { room: RoomId; direction: Direction }[] }
+  /** What happens at 'failed' (e.g. retreat to previous safe room). */
+  onFailed?: { narration: string; retreatTo: RoomId }
+  /** Default narration for wrong-verb attempts not matching any transition. */
+  defaultWrongVerbNarration?: string
+}
+
+export interface World {
+  startingRoom: RoomId
+  startingInventory: ItemId[]
+  rooms: Record<RoomId, Room>
+  items: Record<ItemId, Item>
+  encounters: Record<EncounterId, EncounterDef>
+  /** Story flag definitions and the endings they unlock. */
+  endings: {
+    true: { whenFlags: Record<string, string | boolean | number>; narration: string }
+    wrong: { whenFlags: Record<string, string | boolean | number>; narration: string }
+    bad: { whenFlags: Record<string, string | boolean | number>; narration: string }
+  }
+}