fix(saas-relay): eliminate DATABASE_ERROR by removing DB queries from critical path

Root cause: each relay request executes 13-17 serial DB queries, exhausting
the 50-connection pool under concurrency. When pool is exhausted, sqlx returns
PoolTimedOut which maps to 500 DATABASE_ERROR.

Fixes:
1. log_operation → dispatch_log_operation (async Worker dispatch, non-blocking)
2. record_usage → tokio::spawn (3 DB queries moved off critical path)
3. DB pool: max_connections 50→100 (env-configurable), acquire_timeout 5s→8s

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

crates/zclaw-saas/src/relay/handlers.rs

@@ -9,7 +9,7 @@ use axum::{
 use crate::state::AppState;
 use crate::error::{SaasError, SaasResult};
 use crate::auth::types::AuthContext;
-use crate::auth::handlers::{log_operation, check_permission};
+use crate::auth::handlers::check_permission;
 use crate::model_config::service as model_service;
 use super::{types::*, service};
 
@@ -171,8 +171,11 @@ pub async fn chat_completions(
         max_attempts,
     ).await?;
 
-    log_operation(&state.db, &ctx.account_id, "relay.request", "relay_task", &task.id,
-        Some(serde_json::json!({"model": model_name, "stream": stream})), ctx.client_ip.as_deref()).await?;
+    // 异步派发操作日志（非阻塞，不占用关键路径 DB 连接）
+    state.dispatch_log_operation(
+        &ctx.account_id, "relay.request", "relay_task", &task.id,
+        Some(serde_json::json!({"model": model_name, "stream": stream})), ctx.client_ip.as_deref(),
+    ).await;
 
     // 执行中转 (Key Pool 自动选择 + 429 轮转)
     let response = service::execute_relay(
@@ -183,25 +186,39 @@ pub async fn chat_completions(
         &enc_key,
     ).await;
 
+    // 克隆用于异步 usage 记录
+    let db_usage = state.db.clone();
+    let account_id_usage = ctx.account_id.clone();
+    let provider_id_usage = target_model.provider_id.clone();
+    let model_id_usage = target_model.model_id.clone();
+
     match response {
         Ok(service::RelayResponse::Json(body)) => {
             let (input_tokens, output_tokens) = service::extract_token_usage_from_json(&body);
-            model_service::record_usage(
-                &state.db, &ctx.account_id, &target_model.provider_id,
-                &target_model.model_id, input_tokens, output_tokens,
-                None, "success", None,
-            ).await?;
+            // 异步记录 usage（不阻塞响应）
+            tokio::spawn(async move {
+                if let Err(e) = model_service::record_usage(
+                    &db_usage, &account_id_usage, &provider_id_usage,
+                    &model_id_usage, input_tokens, output_tokens,
+                    None, "success", None,
+                ).await {
+                    tracing::warn!("Failed to record relay usage: {}", e);
+                }
+            });
 
             Ok((StatusCode::OK, [(axum::http::header::CONTENT_TYPE, "application/json")], body).into_response())
         }
         Ok(service::RelayResponse::Sse(body)) => {
-            // SSE 流的 usage 统计在 service 层异步处理
-            // 这里先记录一个占位记录，实际值会在流结束后更新
-            model_service::record_usage(
-                &state.db, &ctx.account_id, &target_model.provider_id,
-                &target_model.model_id, 0, 0,
-                None, "streaming", None,
-            ).await?;
+            // 异步记录 SSE 占位 usage
+            tokio::spawn(async move {
+                if let Err(e) = model_service::record_usage(
+                    &db_usage, &account_id_usage, &provider_id_usage,
+                    &model_id_usage, 0, 0,
+                    None, "streaming", None,
+                ).await {
+                    tracing::warn!("Failed to record SSE usage placeholder: {}", e);
+                }
+            });
 
             let response = axum::response::Response::builder()
                 .status(StatusCode::OK)
@@ -213,11 +230,17 @@ pub async fn chat_completions(
             Ok(response)
         }
         Err(e) => {
-            model_service::record_usage(
-                &state.db, &ctx.account_id, &target_model.provider_id,
-                &target_model.model_id, 0, 0,
-                None, "failed", Some(&e.to_string()),
-            ).await?;
+            // 异步记录失败 usage（不阻塞错误响应）
+            let error_msg = e.to_string();
+            tokio::spawn(async move {
+                if let Err(e2) = model_service::record_usage(
+                    &db_usage, &account_id_usage, &provider_id_usage,
+                    &model_id_usage, 0, 0,
+                    None, "failed", Some(&error_msg),
+                ).await {
+                    tracing::warn!("Failed to record relay failure usage: {}", e2);
+                }
+            });
             Err(e)
         }
     }
@@ -347,8 +370,11 @@ pub async fn retry_task(
         }
     });
 
-    log_operation(&state.db, &ctx.account_id, "relay.retry", "relay_task", &id,
-        None, ctx.client_ip.as_deref()).await?;
+    // 异步派发操作日志
+    state.dispatch_log_operation(
+        &ctx.account_id, "relay.retry", "relay_task", &id,
+        None, ctx.client_ip.as_deref(),
+    ).await;
 
     Ok(Json(serde_json::json!({"ok": true, "task_id": id})))
 }
@@ -407,9 +433,12 @@ pub async fn add_provider_key(
         req.priority, req.max_rpm, req.max_tpm,
     ).await?;
 
-    log_operation(&state.db, &ctx.account_id, "provider_key.add", "provider_key", &key_id,
+    // 异步派发操作日志
+    state.dispatch_log_operation(
+        &ctx.account_id, "provider_key.add", "provider_key", &key_id,
         Some(serde_json::json!({"provider_id": provider_id, "label": req.key_label})),
-        ctx.client_ip.as_deref()).await?;
+        ctx.client_ip.as_deref(),
+    ).await;
 
     Ok(Json(serde_json::json!({"ok": true, "key_id": key_id})))
 }
@@ -430,9 +459,12 @@ pub async fn toggle_provider_key(
 
     super::key_pool::toggle_key_active(&state.db, &key_id, req.active).await?;
 
-    log_operation(&state.db, &ctx.account_id, "provider_key.toggle", "provider_key", &key_id,
+    // 异步派发操作日志
+    state.dispatch_log_operation(
+        &ctx.account_id, "provider_key.toggle", "provider_key", &key_id,
         Some(serde_json::json!({"provider_id": provider_id, "active": req.active})),
-        ctx.client_ip.as_deref()).await?;
+        ctx.client_ip.as_deref(),
+    ).await;
 
     Ok(Json(serde_json::json!({"ok": true})))
 }
@@ -447,9 +479,12 @@ pub async fn delete_provider_key(
 
     super::key_pool::delete_provider_key(&state.db, &key_id).await?;
 
-    log_operation(&state.db, &ctx.account_id, "provider_key.delete", "provider_key", &key_id,
+    // 异步派发操作日志
+    state.dispatch_log_operation(
+        &ctx.account_id, "provider_key.delete", "provider_key", &key_id,
         Some(serde_json::json!({"provider_id": provider_id})),
-        ctx.client_ip.as_deref()).await?;
+        ctx.client_ip.as_deref(),
+    ).await;
 
     Ok(Json(serde_json::json!({"ok": true})))
 }