sequenceDiagram
    participant C1 as Concurrent Request 1
    participant C2 as Concurrent Request 2
    participant DB as PostgreSQL Database
    
    Note over C1,C2: Both compute same stateHash for identical workflows
    
    C1->>DB: INSERT with UUID-1<br/>ON CONFLICT (workflowId, stateHash)<br/>DO UPDATE SET stateData
    C2->>DB: INSERT with UUID-2<br/>ON CONFLICT (workflowId, stateHash)<br/>DO UPDATE SET stateData
    
    Note over DB: Unique index on (workflowId, stateHash)<br/>ensures atomicity
    
    alt First request wins
        DB-->>C1: Returns snapshot with UUID-1
        DB-->>C2: Returns existing snapshot with UUID-1
        Note over C1: isNew = true (UUID matches)
        Note over C2: isNew = false (UUID differs)
    else Second request wins
        DB-->>C2: Returns snapshot with UUID-2
        DB-->>C1: Returns existing snapshot with UUID-2
        Note over C2: isNew = true (UUID matches)
        Note over C1: isNew = false (UUID differs)
    end