diff --git a/crates/zclaw-saas/src/cache.rs b/crates/zclaw-saas/src/cache.rs
index 6d6379e..f35ae35 100644
--- a/crates/zclaw-saas/src/cache.rs
+++ b/crates/zclaw-saas/src/cache.rs
@@ -84,52 +84,60 @@ impl AppCache {
         }
     }
 
-    /// 从 DB 全量加载 models + providers
+    /// 从 DB 全量加载 models + providers + model_groups
+    ///
+    /// 使用 insert-then-retain 模式避免 clear+repopulate 竞态窗口：
+    /// 先插入所有新数据（覆盖旧值），再删除不在新数据中的陈旧条目。
+    /// 这确保缓存从不出现空窗期。
     pub async fn load_from_db(&self, db: &PgPool) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
-        // Load providers
+        use std::collections::HashSet;
+
+        // Load providers — insert-then-retain 避免空窗
         let provider_rows: Vec<(String, String, String, String, String, bool)> = sqlx::query_as(
             "SELECT id, name, display_name, base_url, api_protocol, enabled FROM providers"
         ).fetch_all(db).await?;
 
-        self.providers.clear();
-        for (id, name, display_name, base_url, api_protocol, enabled) in provider_rows {
+        let provider_keys: HashSet<String> = provider_rows.iter().map(|(id, ..)| id.clone()).collect();
+        for (id, name, display_name, base_url, api_protocol, enabled) in &provider_rows {
             self.providers.insert(id.clone(), CachedProvider {
-                id,
-                name,
-                display_name,
-                base_url,
-                api_protocol,
-                enabled,
+                id: id.clone(),
+                name: name.clone(),
+                display_name: display_name.clone(),
+                base_url: base_url.clone(),
+                api_protocol: api_protocol.clone(),
+                enabled: *enabled,
             });
         }
+        self.providers.retain(|k, _| provider_keys.contains(k));
 
-        // Load models (key = model_id for relay lookup)
+        // Load models (key = model_id for relay lookup) — insert-then-retain
         let model_rows: Vec<(String, String, String, String, i64, i64, bool, bool, bool, f64, f64)> = sqlx::query_as(
             "SELECT id, provider_id, model_id, alias, context_window, max_output_tokens,
                     supports_streaming, supports_vision, enabled, pricing_input, pricing_output
              FROM models"
         ).fetch_all(db).await?;
 
-        self.models.clear();
+        let model_keys: HashSet<String> = model_rows.iter().map(|(_, _, mid, ..)| mid.clone()).collect();
         for (id, provider_id, model_id, alias, context_window, max_output_tokens,
-             supports_streaming, supports_vision, enabled, pricing_input, pricing_output) in model_rows
+             supports_streaming, supports_vision, enabled, pricing_input, pricing_output) in &model_rows
         {
             self.models.insert(model_id.clone(), CachedModel {
-                id,
-                provider_id,
+                id: id.clone(),
+                provider_id: provider_id.clone(),
                 model_id: model_id.clone(),
-                alias,
-                context_window,
-                max_output_tokens,
-                supports_streaming,
-                supports_vision,
-                enabled,
-                pricing_input,
-                pricing_output,
+                alias: alias.clone(),
+                context_window: *context_window,
+                max_output_tokens: *max_output_tokens,
+                supports_streaming: *supports_streaming,
+                supports_vision: *supports_vision,
+                enabled: *enabled,
+                pricing_input: *pricing_input,
+                pricing_output: *pricing_output,
             });
         }
+        self.models.retain(|k, _| model_keys.contains(k));
 
-        // Load model groups with members
+        // Load model groups with members — insert-then-retain
         let group_rows: Vec<(String, String, String, String, bool, String)> = sqlx::query_as(
             "SELECT id, name, display_name, COALESCE(description, ''), enabled, COALESCE(failover_strategy, 'quota_aware') FROM model_groups"
         ).fetch_all(db).await?;
@@ -139,7 +147,7 @@ impl AppCache {
              FROM model_group_members ORDER BY priority ASC"
         ).fetch_all(db).await?;
 
-        self.model_groups.clear();
+        let group_keys: HashSet<String> = group_rows.iter().map(|(_, name, ..)| name.clone()).collect();
         for (id, name, display_name, description, enabled, failover_strategy) in &group_rows {
             let members: Vec<CachedGroupMember> = member_rows.iter()
                 .filter(|(_, gid, _, _, _, _)| gid == id)
@@ -161,6 +169,7 @@ impl AppCache {
                 members,
             });
         }
+        self.model_groups.retain(|k, _| group_keys.contains(k));
 
         tracing::info!(
             "Cache loaded: {} providers, {} models, {} model groups",
diff --git a/crates/zclaw-saas/src/error.rs b/crates/zclaw-saas/src/error.rs
index 778feaa..6d3d876 100644
--- a/crates/zclaw-saas/src/error.rs
+++ b/crates/zclaw-saas/src/error.rs
@@ -64,6 +64,18 @@ pub enum SaasError {
 }
 
 impl SaasError {
+    /// 将 sqlx::Error 中的 unique violation 映射为 AlreadyExists (409)，
+    /// 其他 DB 错误保持为 Database (500)。
+    pub fn from_sqlx_unique(e: sqlx::Error, context: &str) -> Self {
+        if let sqlx::Error::Database(ref db_err) = e {
+            // PostgreSQL unique_violation = "23505"
+            if db_err.code().map(|c| c == "23505").unwrap_or(false) {
+                return Self::AlreadyExists(format!("{}已存在", context));
+            }
+        }
+        Self::Database(e)
+    }
+
     /// 获取 HTTP 状态码
     pub fn status_code(&self) -> StatusCode {
         match self {
diff --git a/crates/zclaw-saas/src/model_config/handlers.rs b/crates/zclaw-saas/src/model_config/handlers.rs
index 5cb29a2..341cbd1 100644
--- a/crates/zclaw-saas/src/model_config/handlers.rs
+++ b/crates/zclaw-saas/src/model_config/handlers.rs
@@ -368,7 +368,7 @@ pub async fn remove_group_member(
     Extension(ctx): Extension<AuthContext>,
 ) -> SaasResult<Json<serde_json::Value>> {
     check_permission(&ctx, "model:manage")?;
-    service::remove_group_member(&state.db, &mid).await?;
+    service::remove_group_member(&state.db, &id, &mid).await?;
     log_operation(&state.db, &ctx.account_id, "model_group.remove_member", "model_group", &id,
         Some(serde_json::json!({"member_id": mid})), ctx.client_ip.as_deref()).await?;
     if let Err(e) = state.cache.load_from_db(&state.db).await {
diff --git a/crates/zclaw-saas/src/model_config/service.rs b/crates/zclaw-saas/src/model_config/service.rs
index 6123a73..b894ffe 100644
--- a/crates/zclaw-saas/src/model_config/service.rs
+++ b/crates/zclaw-saas/src/model_config/service.rs
@@ -95,7 +95,7 @@ pub async fn create_provider(db: &PgPool, req: &CreateProviderRequest, enc_key:
     )
     .bind(&id).bind(&req.name).bind(&req.display_name).bind(&encrypted_api_key)
     .bind(&req.base_url).bind(&req.api_protocol).bind(&req.rate_limit_rpm).bind(&req.rate_limit_tpm).bind(&now)
-    .execute(db).await?;
+    .execute(db).await.map_err(|e| SaasError::from_sqlx_unique(e, &format!("Provider '{}'", req.name)))?;
 
     get_provider(db, &id).await
 }
@@ -210,6 +210,15 @@ pub async fn create_model(db: &PgPool, req: &CreateModelRequest) -> SaasResult<M
         )));
     }
 
+    // M-2: 检查 model_id 不与模型组名冲突（避免路由歧义）
+    let group_conflict: Option<(String,)> = sqlx::query_as("SELECT id FROM model_groups WHERE name = $1")
+        .bind(&req.model_id).fetch_optional(db).await?;
+    if group_conflict.is_some() {
+        return Err(SaasError::InvalidInput(
+            format!("模型 ID '{}' 与已有模型组名称冲突，请使用不同的 ID", req.model_id)
+        ));
+    }
+
     let ctx = req.context_window.unwrap_or(8192);
     let max_out = req.max_output_tokens.unwrap_or(4096);
     let streaming = req.supports_streaming.unwrap_or(true);
@@ -223,7 +232,7 @@ pub async fn create_model(db: &PgPool, req: &CreateModelRequest) -> SaasResult<M
     )
     .bind(&id).bind(&req.provider_id).bind(&req.model_id).bind(&req.alias)
     .bind(ctx).bind(max_out).bind(streaming).bind(vision).bind(pi).bind(po).bind(&now)
-    .execute(db).await?;
+    .execute(db).await.map_err(|e| SaasError::from_sqlx_unique(e, &format!("模型 '{}' 在 Provider '{}'", req.model_id, req.provider_id)))?;
 
     get_model(db, &id).await
 }
@@ -548,6 +557,14 @@ pub async fn get_model_group(db: &PgPool, group_id: &str) -> SaasResult<ModelGro
 }
 
 pub async fn create_model_group(db: &PgPool, req: &CreateModelGroupRequest) -> SaasResult<ModelGroupInfo> {
+    // M-S1: failover_strategy 白名单校验
+    const VALID_STRATEGIES: &[&str] = &["quota_aware", "priority", "random"];
+    if !VALID_STRATEGIES.contains(&req.failover_strategy.as_str()) {
+        return Err(SaasError::InvalidInput(
+            format!("failover_strategy 必须是 {:?} 之一", VALID_STRATEGIES)
+        ));
+    }
+
     let id = uuid::Uuid::new_v4().to_string();
     let now = chrono::Utc::now().to_rfc3339();
 
@@ -573,7 +590,7 @@ pub async fn create_model_group(db: &PgPool, req: &CreateModelGroupRequest) -> S
     )
     .bind(&id).bind(&req.name).bind(&req.display_name).bind(&req.description)
     .bind(&req.failover_strategy).bind(&now)
-    .execute(db).await?;
+    .execute(db).await.map_err(|e| SaasError::from_sqlx_unique(e, &format!("模型组 '{}'", req.name)))?;
 
     get_model_group(db, &id).await
 }
@@ -630,13 +647,25 @@ pub async fn add_group_member(
         .bind(&req.model_id).fetch_optional(db).await?
         .ok_or_else(|| SaasError::NotFound(format!("模型 {} 不存在", req.model_id)))?;
 
+    // M-S4: 检查重复成员（避免 DB unique violation 返回 500）
+    let duplicate: Option<(String,)> = sqlx::query_as(
+        "SELECT id FROM model_group_members WHERE group_id = $1 AND provider_id = $2 AND model_id = $3"
+    )
+    .bind(group_id).bind(&req.provider_id).bind(&req.model_id)
+    .fetch_optional(db).await?;
+    if duplicate.is_some() {
+        return Err(SaasError::AlreadyExists(
+            format!("Provider {} 的模型 {} 已在该模型组中", req.provider_id, req.model_id)
+        ));
+    }
+
     let id = uuid::Uuid::new_v4().to_string();
     sqlx::query(
         "INSERT INTO model_group_members (id, group_id, provider_id, model_id, priority, created_at, updated_at)
          VALUES ($1, $2, $3, $4, $5, NOW(), NOW())"
     )
     .bind(&id).bind(group_id).bind(&req.provider_id).bind(&req.model_id).bind(req.priority)
-    .execute(db).await?;
+    .execute(db).await.map_err(|e| SaasError::from_sqlx_unique(e, &format!("Provider {} 的模型 {} 在该模型组", req.provider_id, req.model_id)))?;
 
     Ok(ModelGroupMemberInfo {
         id,
@@ -647,11 +676,12 @@ pub async fn add_group_member(
     })
 }
 
-pub async fn remove_group_member(db: &PgPool, member_id: &str) -> SaasResult<()> {
-    let result = sqlx::query("DELETE FROM model_group_members WHERE id = $1")
-        .bind(member_id).execute(db).await?;
+pub async fn remove_group_member(db: &PgPool, group_id: &str, member_id: &str) -> SaasResult<()> {
+    // M-5: 验证成员确实属于该组
+    let result = sqlx::query("DELETE FROM model_group_members WHERE id = $1 AND group_id = $2")
+        .bind(member_id).bind(group_id).execute(db).await?;
     if result.rows_affected() == 0 {
-        return Err(SaasError::NotFound(format!("成员 {} 不存在", member_id)));
+        return Err(SaasError::NotFound(format!("成员 {} 不属于该模型组", member_id)));
     }
     Ok(())
 }
diff --git a/crates/zclaw-saas/src/relay/handlers.rs b/crates/zclaw-saas/src/relay/handlers.rs
index 354f213..16a703f 100644
--- a/crates/zclaw-saas/src/relay/handlers.rs
+++ b/crates/zclaw-saas/src/relay/handlers.rs
@@ -15,7 +15,6 @@ use super::{types::*, service};
 
 /// POST /api/v1/relay/chat/completions
 /// OpenAI 兼容的聊天补全端点
-#[axum::debug_handler]
 pub async fn chat_completions(
     State(state): State<AppState>,
     Extension(ctx): Extension<AuthContext>,
@@ -215,6 +214,7 @@ pub async fn chat_completions(
                 &state.db, &task.id, &candidate.provider_id,
                 &candidate.base_url, &request_body, stream,
                 max_attempts, retry_delay_ms, &enc_key,
+                true, // 独立调用，管理 task 状态
             ).await {
                 Ok(resp) => Ok((resp, candidate.provider_id.clone(), candidate.model_id.clone())),
                 Err(e) => Err(e),
@@ -397,14 +397,21 @@ pub async fn list_available_models(
         if !group.enabled {
             continue;
         }
-        // 所有成员都支持 streaming → 模型组支持 streaming
-        let all_streaming = group.members.iter().all(|m| {
+        // H-2: 过滤无可用成员的模型组，避免前端选择后请求失败
+        let active_members: Vec<_> = group.members.iter()
+            .filter(|m| m.enabled)
+            .collect();
+        if active_members.is_empty() {
+            continue;
+        }
+        // 所有 active 成员都支持 streaming → 模型组支持 streaming
+        let all_streaming = active_members.iter().all(|m| {
             state.cache.get_model(&m.model_id)
                 .map(|cm| cm.supports_streaming)
                 .unwrap_or(true)
         });
-        // 任一成员支持 vision → 模型组支持 vision
-        let any_vision = group.members.iter().any(|m| {
+        // 任一 active 成员支持 vision → 模型组支持 vision
+        let any_vision = active_members.iter().any(|m| {
             state.cache.get_model(&m.model_id)
                 .map(|cm| cm.supports_vision)
                 .unwrap_or(false)
@@ -439,9 +446,6 @@ pub async fn retry_task(
         )));
     }
 
-    // 获取 provider 信息
-    let provider = model_service::get_provider(&state.db, &task.provider_id).await?;
-
     // 读取原始请求体
     let request_body: Option<String> = sqlx::query_scalar(
         "SELECT request_body FROM relay_tasks WHERE id = $1"
@@ -453,17 +457,80 @@ pub async fn retry_task(
 
     let body = request_body.ok_or_else(|| SaasError::Internal("任务请求体丢失".into()))?;
 
-    // 从 request body 解析 stream 标志
-    let stream: bool = serde_json::from_str::<serde_json::Value>(&body)
-        .ok()
+    // 从 request body 解析 stream 标志和 model 字段
+    let parsed_body: Option<serde_json::Value> = serde_json::from_str(&body).ok();
+    let stream: bool = parsed_body.as_ref()
         .and_then(|v| v.get("stream").and_then(|s| s.as_bool()))
         .unwrap_or(false);
+    let model_name: Option<String> = parsed_body.as_ref()
+        .and_then(|v| v.get("model").and_then(|m| m.as_str()).map(|s| s.to_string()));
+
+    // H-8: 重新解析模型组 — 如果原始请求使用模型组，重试时走 failover 路径
+    // 而不是盲目使用存储的（可能已失败的）provider_id
+    let mut model_resolution = if let Some(ref name) = model_name {
+        if let Some(group) = state.cache.get_model_group(name) {
+            // 模型组：构建候选列表
+            let mut candidates: Vec<CandidateModel> = Vec::new();
+            for member in &group.members {
+                if !member.enabled { continue; }
+                let provider = match state.cache.get_provider(&member.provider_id) {
+                    Some(p) => p,
+                    None => continue,
+                };
+                let physical_model = match state.cache.get_model(&member.model_id) {
+                    Some(m) => m,
+                    None => continue,
+                };
+                candidates.push(CandidateModel {
+                    provider_id: member.provider_id.clone(),
+                    model_id: member.model_id.clone(),
+                    base_url: provider.base_url.clone(),
+                    supports_streaming: physical_model.supports_streaming,
+                });
+            }
+            if candidates.is_empty() {
+                return Err(SaasError::NotFound(
+                    format!("模型组 '{}' 没有可用的候选 Provider（重试时解析）", name)
+                ));
+            }
+            ModelResolution::Group(candidates)
+        } else if let Some(target_model) = state.cache.get_model(name) {
+            // 直接模型
+            let provider = state.cache.get_provider(&target_model.provider_id)
+                .ok_or_else(|| SaasError::NotFound(format!("Provider {} 不存在（重试时解析）", target_model.provider_id)))?;
+            ModelResolution::Direct(CandidateModel {
+                provider_id: target_model.provider_id.clone(),
+                model_id: target_model.model_id.clone(),
+                base_url: provider.base_url.clone(),
+                supports_streaming: target_model.supports_streaming,
+            })
+        } else {
+            // 无法解析，回退到存储的 provider_id（向后兼容）
+            let provider = model_service::get_provider(&state.db, &task.provider_id).await?;
+            ModelResolution::Direct(CandidateModel {
+                provider_id: task.provider_id.clone(),
+                model_id: task.model_id.clone(),
+                base_url: provider.base_url.clone(),
+                supports_streaming: true,
+            })
+        }
+    } else {
+        // 无 model 字段，回退到存储的 provider_id
+        let provider = model_service::get_provider(&state.db, &task.provider_id).await?;
+        ModelResolution::Direct(CandidateModel {
+            provider_id: task.provider_id.clone(),
+            model_id: task.model_id.clone(),
+            base_url: provider.base_url.clone(),
+            supports_streaming: true,
+        })
+    };
 
     let max_attempts = task.max_attempts as u32;
     let config = state.config.read().await;
     let base_delay_ms = config.relay.retry_delay_ms;
     let enc_key = config.api_key_encryption_key()
         .map_err(|e| SaasError::Internal(e.to_string()))?;
+    drop(config);
 
     // 重置任务状态为 queued 以允许新的 processing
     sqlx::query(
@@ -473,17 +540,30 @@ pub async fn retry_task(
     .execute(&state.db)
     .await?;
 
-    // 异步执行重试 (Key Pool 自动选择)
+    // 异步执行重试 — 根据解析结果选择执行路径
     let db = state.db.clone();
     let task_id = id.clone();
-    let provider_id = task.provider_id.clone();
-    let base_url = provider.base_url.clone();
     tokio::spawn(async move {
-        match service::execute_relay(
-            &db, &task_id, &provider_id,
-            &base_url, &body, stream,
-            max_attempts, base_delay_ms, &enc_key,
-        ).await {
+        let result = match model_resolution {
+            ModelResolution::Direct(ref candidate) => {
+                service::execute_relay(
+                    &db, &task_id, &candidate.provider_id,
+                    &candidate.base_url, &body, stream,
+                    max_attempts, base_delay_ms, &enc_key,
+                    true,
+                ).await
+            }
+            ModelResolution::Group(ref mut candidates) => {
+                service::sort_candidates_by_quota(&db, candidates).await;
+                service::execute_relay_with_failover(
+                    &db, &task_id, candidates,
+                    &body, stream,
+                    max_attempts, base_delay_ms, &enc_key,
+                ).await
+                .map(|(resp, _, _)| resp)
+            }
+        };
+        match result {
             Ok(_) => tracing::info!("Relay task {} 重试成功", task_id),
             Err(e) => tracing::warn!("Relay task {} 重试失败: {}", task_id, e),
         }
@@ -544,7 +624,7 @@ pub async fn add_provider_key(
     }
 
     // Encrypt the API key before storing in database
-    let enc_key = state.config.read().await.totp_encryption_key()?;
+    let enc_key = state.config.read().await.api_key_encryption_key()?;
     let encrypted_value = crate::crypto::encrypt_value(&req.key_value, &enc_key)?;
 
     let key_id = super::key_pool::add_provider_key(
diff --git a/crates/zclaw-saas/src/relay/service.rs b/crates/zclaw-saas/src/relay/service.rs
index a4d33f0..4cdb2c3 100644
--- a/crates/zclaw-saas/src/relay/service.rs
+++ b/crates/zclaw-saas/src/relay/service.rs
@@ -202,6 +202,9 @@ pub async fn execute_relay(
     max_attempts: u32,
     base_delay_ms: u64,
     enc_key: &[u8; 32],
+    // 当由 `execute_relay_with_failover` 调用时为 false，由外层统一管理 task 状态；
+    // 独立调用时为 true，由本函数管理 task 状态。
+    manage_task_status: bool,
 ) -> SaasResult<RelayResponse> {
     validate_provider_url(provider_base_url).await?;
 
@@ -234,7 +237,7 @@ pub async fn execute_relay(
 
     for attempt in 0..max_attempts {
         let is_first = attempt == 0;
-        if is_first {
+        if is_first && manage_task_status {
             update_task_status(db, task_id, "processing", None, None, None).await?;
         }
 
@@ -254,7 +257,9 @@ pub async fn execute_relay(
                 Err(SaasError::RateLimited(msg)) => {
                     // 所有 Key 均在冷却中
                     let err_msg = format!("Key Pool 耗尽: {}", msg);
-                    update_task_status(db, task_id, "failed", None, None, Some(&err_msg)).await?;
+                    if manage_task_status {
+                        update_task_status(db, task_id, "failed", None, None, Some(&err_msg)).await?;
+                    }
                     return Err(SaasError::RateLimited(msg));
                 }
                 Err(e) => return Err(e),
@@ -377,8 +382,10 @@ pub async fn execute_relay(
                 } else {
                     let body = resp.text().await.unwrap_or_default();
                     let (input_tokens, output_tokens) = extract_token_usage(&body);
-                    update_task_status(db, task_id, "completed",
-                        Some(input_tokens), Some(output_tokens), None).await?;
+                    if manage_task_status {
+                        update_task_status(db, task_id, "completed",
+                            Some(input_tokens), Some(output_tokens), None).await?;
+                    }
                     // 记录 Key 使用量（失败仅记录，不阻塞响应）
                     if let Err(e) = super::key_pool::record_key_usage(
                         db, &key_id, Some(input_tokens + output_tokens),
@@ -411,7 +418,9 @@ pub async fn execute_relay(
                             "Key Pool 轮转耗尽 ({} attempts)，所有 Key 均被限流",
                             max_attempts
                         );
-                        update_task_status(db, task_id, "failed", None, None, Some(&err_msg)).await?;
+                        if manage_task_status {
+                            update_task_status(db, task_id, "failed", None, None, Some(&err_msg)).await?;
+                        }
                         return Err(SaasError::RateLimited(err_msg));
                     }
 
@@ -425,7 +434,9 @@ pub async fn execute_relay(
                 if !is_retryable_status(status) || attempt + 1 >= max_attempts {
                     let body = resp.text().await.unwrap_or_default();
                     let err_msg = format!("上游返回 HTTP {}: {}", status, &body[..body.len().min(500)]);
-                    update_task_status(db, task_id, "failed", None, None, Some(&err_msg)).await?;
+                    if manage_task_status {
+                        update_task_status(db, task_id, "failed", None, None, Some(&err_msg)).await?;
+                    }
                     return Err(SaasError::Relay(err_msg));
                 }
                 tracing::warn!(
@@ -436,7 +447,9 @@ pub async fn execute_relay(
             Err(e) => {
                 if !is_retryable_error(&e) || attempt + 1 >= max_attempts {
                     let err_msg = format!("请求上游失败: {}", e);
-                    update_task_status(db, task_id, "failed", None, None, Some(&err_msg)).await?;
+                    if manage_task_status {
+                        update_task_status(db, task_id, "failed", None, None, Some(&err_msg)).await?;
+                    }
                     return Err(SaasError::Relay(err_msg));
                 }
                 tracing::warn!(
@@ -479,6 +492,9 @@ pub async fn execute_relay_with_failover(
     let failover_start = std::time::Instant::now();
     const FAILOVER_TIMEOUT: Duration = Duration::from_secs(60);
 
+    // C-3: 外层统一管理 task 状态 — 仅设一次 "processing"
+    update_task_status(db, task_id, "processing", None, None, None).await?;
+
     for (idx, candidate) in candidates.iter().enumerate() {
         // M-3: 超时预算检查 — 防止级联失败累积过长
         if failover_start.elapsed() >= FAILOVER_TIMEOUT {
@@ -502,6 +518,7 @@ pub async fn execute_relay_with_failover(
             max_attempts_per_provider,
             base_delay_ms,
             enc_key,
+            false, // C-3: 外层管理 task 状态
         )
         .await
         {
@@ -542,9 +559,15 @@ pub async fn execute_relay_with_failover(
         }
     }
 
-    Err(last_error.unwrap_or(SaasError::RateLimited(
+    // C-3: 所有候选失败 — 外层统一标记 task 为 "failed"
+    let final_error = last_error.unwrap_or_else(|| SaasError::RateLimited(
         "所有候选 Provider 均不可用".into(),
-    )))
+    ));
+    let err_msg = format!("{}", final_error);
+    if let Err(e) = update_task_status(db, task_id, "failed", None, None, Some(&err_msg)).await {
+        tracing::warn!("Failed to update task {} status after failover exhaustion: {}", task_id, e);
+    }
+    Err(final_error)
 }
 
 /// 替换 JSON body 中的 "model" 字段为当前候选的物理模型 ID
@@ -627,12 +650,15 @@ pub async fn sort_candidates_by_quota(
 
         let map: HashMap<String, i64> = quota_rows.into_iter().collect();
 
-        // 更新缓存
+        // 更新缓存 + 清理过期条目
         {
             let mut cache_guard = cache.lock().unwrap();
             for (pid, remaining) in &map {
                 cache_guard.insert(pid.clone(), (*remaining, now));
             }
+            // M-S3: 清理超过 TTL 5x（25s）的陈旧条目，防止已删除 Provider 的条目永久残留
+            let ttl_5x = QUOTA_CACHE_TTL * 5;
+            cache_guard.retain(|_, (_, ts)| now.saturating_duration_since(*ts) < ttl_5x);
         }
 
         map