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doc/protocol.md

@@ -37,6 +37,14 @@ OHLC periods are represented as seconds.
 * Relay subscribes to Flink (XSUB) and fanouts to clients (XPUB)
 * Clients subscribe to specific tickers
 
+### Symbol Metadata Update Flow (Flink → Gateways)
+* Ingestors write symbol metadata to Kafka
+* Flink reads from Kafka, writes to Iceberg symbol_metadata table
+* After committing to Iceberg, Flink publishes SymbolMetadataUpdated notification on MARKET_DATA_PUB
+* Gateways subscribe to METADATA_UPDATE topic on startup
+* Upon receiving notification, gateways reload symbol metadata from Iceberg
+* This prevents race conditions where gateways start before symbol metadata is available
+
 ### Data Processing (Kafka → Flink → Iceberg)
 * All market data flows through Kafka (durable event log)
 * Flink processes streams for aggregations and CEP
@@ -90,10 +98,11 @@ All sockets bind on **Relay** (well-known endpoint). Components connect to relay
 - **Socket Type**:
   - Relay XPUB (bind) ← Clients SUB (connect) - Port 5558
   - Relay XSUB (connect) → Flink PUB (bind) - Port 5557
-- **Message Types**: `Tick`, `OHLC`, `HistoryReadyNotification`
+- **Message Types**: `Tick`, `OHLC`, `HistoryReadyNotification`, `SymbolMetadataUpdated`
 - **Topic Formats**:
   - Market data: `{ticker}|{data_type}` (e.g., `BINANCE:BTC/USDT|tick`)
   - Notifications: `RESPONSE:{client_id}` or `HISTORY_READY:{request_id}`
+  - System notifications: `METADATA_UPDATE` (for symbol metadata updates)
 - **Behavior**:
   - Clients subscribe to ticker topics and notification topics via Relay XPUB
   - Relay forwards subscriptions to Flink via XSUB
@@ -150,6 +159,7 @@ The two-frame envelope is the **logical protocol format**, but physical transmis
 | 0x10    | SubmitHistoricalRequest   | Client request for historical data (async)     |
 | 0x11    | SubmitResponse            | Immediate ack with notification topic          |
 | 0x12    | HistoryReadyNotification  | Notification that data is ready in Iceberg     |
+| 0x13    | SymbolMetadataUpdated     | Notification that symbol metadata refreshed    |
 
 ## User Container Event System
 
@@ -355,6 +365,11 @@ enum AckStatus {
 }
 ```
 
+### Language Notes
+- JavaScript protobufs will convert field names to camelCase.
+- Python will retain snake_case.
+
+
 ### Delivery Examples
 
 ```python