sequenceDiagram
    participant Client
    participant API as Execute API
    participant PreProc as preprocessExecution
    participant Billing as Subscription Service
    participant Limits as Execution Limits
    participant Executor as Workflow Executor
    participant Logger as Logging Session

    Client->>API: POST /api/workflows/{id}/execute
    API->>PreProc: preprocessExecution(workflowId, userId)
    PreProc->>Billing: getHighestPrioritySubscription(userId)
    Billing-->>PreProc: userSubscription (plan: free|pro|team|enterprise)
    PreProc->>Limits: getExecutionTimeout(plan, 'sync')
    Limits-->>PreProc: timeout (5min|60min)
    PreProc->>Limits: getExecutionTimeout(plan, 'async')
    Limits-->>PreProc: timeout (90min)
    PreProc-->>API: executionTimeout: {sync, async}
    
    alt SSE Execution
        API->>API: Setup AbortController + setTimeout(syncTimeout)
        API->>Executor: executeWorkflow(abortSignal)
        alt Timeout Occurs
            API->>Executor: abortController.abort()
            Executor-->>API: result.status = 'cancelled'
            API->>Logger: markAsFailed(timeoutErrorMessage)
            API->>Client: SSE execution:error (408)
        else Success
            Executor-->>API: result (outputs, logs)
            API->>Logger: complete()
            API->>Client: SSE execution:completed
        end
    else Non-SSE Execution
        API->>Executor: executeWorkflow(AbortSignal.timeout(syncTimeout))
        alt Timeout Occurs
            Executor-->>API: throws TimeoutError
            API->>Limits: isTimeoutError(error)
            Limits-->>API: true
            API->>Limits: getTimeoutErrorMessage(error, syncTimeout)
            Limits-->>API: "Execution timed out after X minutes"
            API->>Logger: safeCompleteWithError()
            API->>Client: JSON error (408)
        else Success
            Executor-->>API: result
            API->>Logger: complete()
            API->>Client: JSON result (200)
        end
    end