flowchart TB P1["Textbook sends POST /xapi/statements
(batch)"]:::before P2["AuthN Token Cache lookup
Redis, 60s TTL; falls back to local LRU on Redis failure"]:::before P3["Tier-1 structural validation
all-or-nothing per batch"]:::before P4["Assign UUIDv7 Statement ID where missing"]:::before P5["Produce to Kafka
acks=all, key = district:student"]:::after OK["Broker acks → 200 with statement IDs"]:::after Fail["Backpressure Queue full AND broker unreachable
→ 503 + Retry-After + page alert"]:::exc P1 --> P2 --> P3 --> P4 --> P5 P5 --> OK P5 --> Fail classDef before fill:#8b9bb0,stroke:#5f6e82,color:#fff,font-size:13px classDef after fill:#2a9d8f,stroke:#1f7a6f,color:#fff,font-size:13px classDef exc fill:#e9a23b,stroke:#b8791f,color:#222,font-size:13px linkStyle default stroke:#999,stroke-width:2px