test(integration): rewrite broker integration tests for cTrader OpenAPI migration

Replace FIX-protocol-based integration tests with tests using real cTrader
types (ICMarketsConfig, TradingOrder, BrokerInterface). All 21 tests pass:
broker_failover (5), icmarkets_validation (10), order_lifecycle (6).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ctrader-openapi/src/orders.rs

@@ -121,6 +121,59 @@ pub fn close_position(account_id: i64, position_id: i64, volume: i64) -> ProtoMe
     }
 }
 
+// ── Execution event parsing ──────────────────────────────────────
+
+/// Parsed execution event info (avoids exposing raw proto types to consumers).
+#[derive(Debug, Clone)]
+pub struct ExecutionEventInfo {
+    /// cTrader order ID.
+    pub order_id: i64,
+    /// Symbol ID.
+    pub symbol_id: i64,
+    /// Trade side as proto enum value (1=Buy, 2=Sell).
+    pub trade_side: i32,
+    /// Volume in cTrader units (cents of lot).
+    pub volume: i64,
+    /// Execution price (for filled orders).
+    pub execution_price: Option<f64>,
+    /// Executed volume in cents.
+    pub executed_volume: Option<i64>,
+    /// Linked position ID (if any).
+    pub position_id: Option<i64>,
+    /// Execution type as proto enum value.
+    pub execution_type: i32,
+    /// Open timestamp (Unix ms).
+    pub timestamp: Option<i64>,
+}
+
+/// Try to parse an execution event from a raw `ProtoMessage`.
+///
+/// Returns `None` if the message is not an execution event or cannot be decoded.
+pub fn parse_execution_event(msg: &ProtoMessage) -> Option<ExecutionEventInfo> {
+    if msg.payload_type != proto::PT_EXECUTION_EVENT {
+        return None;
+    }
+    let payload = msg.payload.as_deref()?;
+    let event = proto::ProtoOaExecutionEvent::decode(payload).ok()?;
+    let order = event.order?;
+    Some(ExecutionEventInfo {
+        order_id: order.order_id,
+        symbol_id: order.trade_data.symbol_id,
+        trade_side: order.trade_data.trade_side,
+        volume: order.trade_data.volume,
+        execution_price: order.execution_price,
+        executed_volume: order.executed_volume,
+        position_id: event.position.map(|p| p.position_id),
+        execution_type: event.execution_type,
+        timestamp: order.trade_data.open_timestamp,
+    })
+}
+
+/// Extract the order ID from an execution response message.
+pub fn extract_order_id(msg: &ProtoMessage) -> Option<i64> {
+    parse_execution_event(msg).map(|e| e.order_id)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

ctrader-openapi/src/symbols.rs

@@ -121,6 +121,14 @@ impl SymbolMapper {
     pub fn is_empty(&self) -> bool {
         self.by_name.is_empty()
     }
+
+    /// Resolve a symbol ID to its name.
+    pub fn symbol_name(&self, id: i64) -> Result<String> {
+        self.by_id
+            .get(&id)
+            .map(|s| s.symbol_name.clone())
+            .ok_or_else(|| CTraderError::UnknownSymbol(format!("id={id}")))
+    }
 }
 
 fn symbol_info_from_light(sym: &ProtoOaLightSymbol) -> SymbolInfo {