feat: define the discovery api wire contract

frontend/src/lib/types.ts

@@ -0,0 +1,79 @@
+// Wire types mirrored against backend/app/api/schemas.py.
+// Field names match the JSON payloads exactly, so they stay snake_case.
+
+export interface HistoryTurn {
+  role: 'user' | 'assistant'
+  content: string
+}
+
+export interface PriorRecommendation {
+  rank: number
+  track_id: string
+  title: string
+  artists: string[]
+}
+
+export interface RecommendationRequest {
+  schema_version: 1
+  query: string
+  history: HistoryTurn[]
+  prior_recommendations: PriorRecommendation[]
+}
+
+export interface TrackCard {
+  id: string
+  uri: string
+  title: string
+  artists: string[]
+  album_name: string
+  album_art_url: string | null
+  external_url: string | null
+}
+
+export interface MetadataEvent {
+  type: 'metadata'
+  request_id: string
+  intent_summary: string
+  candidate_count: number
+}
+
+export interface TrackEvent {
+  type: 'track'
+  rank: number
+  track: TrackCard
+  justification: string
+}
+
+export interface WarningEvent {
+  type: 'warning'
+  code: string
+  message: string
+}
+
+export interface ErrorEvent {
+  type: 'error'
+  code: string
+  message: string
+}
+
+export interface DoneEvent {
+  type: 'done'
+  track_count: number
+  total_ms: number
+}
+
+export type StreamEvent = MetadataEvent | TrackEvent | WarningEvent | ErrorEvent | DoneEvent
+
+export interface PlaylistCreateRequest {
+  schema_version: 1
+  name: string
+  track_uris: string[]
+}
+
+export interface PlaylistCreateResponse {
+  url: string
+}
+
+export interface CurrentUser {
+  display_name: string
+}