Function handleMiniAppReturn

handleMiniAppReturn(
    storage: UserFlowStateManager,
    source: FlowContextSource,
    secret: string,
): Promise<UserFlowState | null>
Resolves persisted flow state from a signed return payload produced by COORD-001 primitives.
Parameters
- storage: UserFlowStateManager
- source: FlowContextSource
- secret: string
Returns Promise<UserFlowState | null>