graph TB
    subgraph "External"
        LLM[LLM API — GPT-4o mini]
        IOS_3RD[ios-3rd-party — Apple APNS]
        IOS_DEV[iOS Device]
    end

    subgraph "UI Layer"
        CLIENT[Client — React + Tailwind]
    end

    subgraph "BE Layer — Resolvers"
        APPSYNC[AWS AppSync]
        COGNITO[AWS Cognito]
        CH[chat-resolver λ]
        UR[user-resolver λ]
        PR[platform-resolver λ]
        DR[device-resolver λ]
        UPR[upload-resolver λ]
        AR[action-resolver λ]
        MTR[message-template-resolver λ]
        TR[tac-resolver λ]
        ALR[action-log-resolver λ]
    end

    subgraph "BE Layer — Workers"
        SQS_UP[upload-processor-sqs]
        UP[upload-processor λ]
        SQS_AT[action-trigger-sqs]
        AT[action-trigger λ]
        CK[checkin-handler λ]
        SQS_CK[checkin-handler-sqs]
    end

    subgraph "Event Layer"
        SNS[device-event-sns]
        SQS_OEM[apple-process-action-sqs]
    end

    subgraph "OEM Layer"
        OEM_L[apple-process-action λ]
        APIGW[fluxion-oem-service — API Gateway]
        CACHE[(ElastiCache Redis)]
    end

    subgraph "Data Layer"
        RDS[(RDS PostgreSQL)]
        S3_ERR[(S3 error-reports)]
    end

    LLM -.-> CH
    CLIENT --> APPSYNC
    CLIENT --> COGNITO
    COGNITO -->|JWT| APPSYNC

    APPSYNC --> CH & UR & PR & DR & UPR & AR & MTR & TR & ALR

    UPR --> SQS_UP --> UP --> RDS
    AR --> SQS_AT --> AT --> RDS
    CH & UR & PR & DR & MTR & TR & ALR --> RDS
    ALR --> S3_ERR

    AT -->|publish| SNS
    SNS --> SQS_OEM --> OEM_L
    OEM_L <--> CACHE
    OEM_L -->|POST /apns| APIGW -->|proxy| IOS_3RD
    IOS_DEV -->|PUT /mdm| APIGW -->|invoke| OEM_L
    OEM_L --> SQS_CK --> CK --> RDS

    CK -->|subscription trigger| APPSYNC
    APPSYNC -->|subscription push| CLIENT

graph TB
    subgraph "AWS Region"
        subgraph "Public"
            CF[CloudFront CDN]
            APPSYNC_SVC[AppSync Service]
            COGNITO_SVC[Cognito User Pool]
            APIGW_SVC[API Gateway — mTLS<br/>MDM endpoint]
        end

        subgraph "Private Subnet"
            LAMBDA_BE[BE Lambdas<br/>resolvers + workers]
            LAMBDA_OEM[OEM Lambda<br/>apple-process-action]
            RDS_PRI[(RDS Primary<br/>db.t3.micro)]
        end

        subgraph "Messaging"
            SNS_SVC[SNS Topics]
            SQS_SVC[SQS Queues + DLQ]
        end

        subgraph "Cache"
            CACHE_SVC[ElastiCache Redis<br/>or DynamoDB]
        end

        CF --> S3_STATIC[S3 Static<br/>React Build]
    end

    INTERNET((Internet)) --> CF
    INTERNET --> APPSYNC_SVC
    IOS((iOS Devices)) -->|mTLS| APIGW_SVC
    APIGW_SVC --> LAMBDA_OEM
    LAMBDA_OEM --> CACHE_SVC
    LAMBDA_OEM --> APNS_EXT((Apple APNS))
    LAMBDA_BE --> LLM_EXT((GPT-4o mini))
    LAMBDA_BE --> RDS_PRI