diff --git a/src/lib/server/osoh-store.ts b/src/lib/server/osoh-store.ts
new file mode 100644
index 0000000..58b87e0
--- /dev/null
+++ b/src/lib/server/osoh-store.ts
@@ -0,0 +1,77 @@
+export type IsoUtcTimestamp = string;
+
+export type OsohMonitoredSurfaceClass = 'external_monitored_surface';
+
+export type OsohSurfaceStatus =
+  | 'inactive'
+  | 'active_monitored_surface'
+  | 'disabled';
+
+export type OsohMonitoringEventType =
+  | 'surface_ping_received'
+  | 'surface_health_changed'
+  | 'surface_token_used'
+  | 'surface_token_revoked';
+
+export type OsohAuditAction =
+  | 'site_created'
+  | 'site_updated'
+  | 'site_disabled'
+  | 'token_created'
+  | 'token_revoked';
+
+export interface OsohMonitoredSiteRecord {
+  siteId: string;
+  siteSlug: string;
+  displayName: string;
+  classification: OsohMonitoredSurfaceClass;
+  status: OsohSurfaceStatus;
+  createdAt: IsoUtcTimestamp;
+  updatedAt: IsoUtcTimestamp;
+}
+
+export interface OsohMonitoredSurfaceTokenRecord {
+  tokenId: string;
+  siteId: string;
+
+  /**
+   * One-way hash only. Never persist raw token material.
+   */
+  tokenHash: string;
+
+  scope: 'ingest';
+  revoked: boolean;
+  createdAt: IsoUtcTimestamp;
+  updatedAt: IsoUtcTimestamp;
+}
+
+export interface OsohMonitoringEventRecord {
+  eventId: string;
+  siteId: string;
+  eventType: OsohMonitoringEventType;
+  occurredAt: IsoUtcTimestamp;
+  receivedAt: IsoUtcTimestamp;
+  payload: Record<string, unknown>;
+}
+
+export interface OsohAuditTrailRecord {
+  auditId: string;
+  siteId: string;
+  action: OsohAuditAction;
+  occurredAt: IsoUtcTimestamp;
+  details: Record<string, unknown>;
+}
+
+export interface OsohStoreState {
+  monitoredSites: OsohMonitoredSiteRecord[];
+  monitoredSurfaceTokens: OsohMonitoredSurfaceTokenRecord[];
+  monitoringEvents: OsohMonitoringEventRecord[];
+  auditTrail: OsohAuditTrailRecord[];
+}
+
+export const createEmptyOsohStoreState = (): OsohStoreState => ({
+  monitoredSites: [],
+  monitoredSurfaceTokens: [],
+  monitoringEvents: [],
+  auditTrail: [],
+});