Persist backend per database id in admin metadata so restarts and lazy opens always use the correct engine (Sled/Redb)

src/rpc.rs

@@ -158,14 +158,42 @@ impl RpcServerImpl {
             ));
         }
 
-        // Create server instance with default options
+        // Resolve effective backend for this db from admin meta or filesystem; fallback to default
+        let meta_backend = admin_meta::get_database_backend(&self.base_dir, self.backend.clone(), &self.admin_secret, db_id)
+            .ok()
+            .flatten();
+        let db_path = std::path::PathBuf::from(&self.base_dir).join(format!("{}.db", db_id));
+        let sniffed_backend = if db_path.exists() {
+            if db_path.is_file() {
+                Some(crate::options::BackendType::Redb)
+            } else if db_path.is_dir() {
+                Some(crate::options::BackendType::Sled)
+            } else {
+                None
+            }
+        } else {
+            None
+        };
+        let effective_backend = meta_backend.clone().or(sniffed_backend).unwrap_or(self.backend.clone());
+        if effective_backend != self.backend {
+            eprintln!(
+                "notice: get_or_create_server: db {} backend resolved to {:?} (server default {:?})",
+                db_id, effective_backend, self.backend
+            );
+        }
+        // If we had to sniff (no meta), persist the resolved backend
+        if meta_backend.is_none() {
+            let _ = admin_meta::set_database_backend(&self.base_dir, self.backend.clone(), &self.admin_secret, db_id, effective_backend.clone());
+        }
+
+        // Create server instance with resolved backend
         let db_option = DBOption {
             dir: self.base_dir.clone(),
             port: 0, // Not used for RPC-managed databases
             debug: false,
             encryption_key: None,
             encrypt: false,
-            backend: self.backend.clone(),
+            backend: effective_backend,
             admin_secret: self.admin_secret.clone(),
         };
 
@@ -308,17 +336,22 @@ impl RpcServer for RpcServerImpl {
             return Err(jsonrpsee::types::ErrorObjectOwned::owned(-32000, format!("Failed to ensure base dir: {}", e), None::<()>));
         }
 
-        // Create server instance using base_dir and admin secret
+        // Map RPC backend to options backend and persist it in admin meta for this db id
+        let opt_backend = match backend {
+            BackendType::Redb => crate::options::BackendType::Redb,
+            BackendType::Sled => crate::options::BackendType::Sled,
+        };
+        admin_meta::set_database_backend(&self.base_dir, self.backend.clone(), &self.admin_secret, db_id, opt_backend.clone())
+            .map_err(|e| jsonrpsee::types::ErrorObjectOwned::owned(-32000, e.0, None::<()>))?;
+
+        // Create server instance using base_dir, chosen backend and admin secret
         let option = DBOption {
             dir: self.base_dir.clone(),
             port: 0, // Not used for RPC-managed databases
             debug: false,
             encryption_key: None,  // per-db key is stored in admin DB 0
             encrypt: false,        // encryption decided per-db at open time
-            backend: match backend {
-                BackendType::Redb => crate::options::BackendType::Redb,
-                BackendType::Sled => crate::options::BackendType::Sled,
-            },
+            backend: opt_backend,
             admin_secret: self.admin_secret.clone(),
         };