reuse redis connection

backend/src/services/cache.rs

@@ -1,20 +1,29 @@
 use redis::AsyncCommands;
 use sha2::{Digest, Sha256};
+use tokio::sync::OnceCell;
 
 /// Redis caching layer implementing the key patterns and TTLs
 /// defined in DATA_MODEL.md section 3.
 pub struct CacheService {
     client: redis::Client,
+    conn: OnceCell<redis::aio::MultiplexedConnection>,
 }
 
 impl CacheService {
     pub fn new(redis_url: &str) -> Result<Self, redis::RedisError> {
         let client = redis::Client::open(redis_url)?;
-        Ok(Self { client })
+        Ok(Self {
+            client,
+            conn: OnceCell::new(),
+        })
     }
 
     async fn conn(&self) -> Result<redis::aio::MultiplexedConnection, redis::RedisError> {
-        self.client.get_multiplexed_async_connection().await
+        let conn = self
+            .conn
+            .get_or_try_init(|| self.client.get_multiplexed_async_connection())
+            .await?;
+        Ok(conn.clone())
     }
 
     // ── Tile cache ──────────────────────────────────────────────