refactor(proxy): remove is_proxy_target in favor of failover_queue

- Remove `is_proxy_target` field from Provider struct (Rust & TypeScript)
- Remove related DAO methods: get_proxy_target_provider, set_proxy_target
- Remove deprecated Tauri commands: get_proxy_targets, set_proxy_target
- Add `is_available()` method to CircuitBreaker for availability checks
  without consuming HalfOpen probe permits (used in select_providers)
- Keep `allow_request()` for actual request gating with permit tracking
- Update stream_check to use failover_queue instead of is_proxy_target
- Clean up commented-out reset circuit breaker button in ProviderActions
- Remove unused useProxyTargets and useSetProxyTarget hooks

src-tauri/src/proxy/circuit_breaker.rs

@@ -99,6 +99,36 @@ impl CircuitBreaker {
         log::debug!("Circuit breaker config updated");
     }
 
+    /// 判断当前 Provider 是否“可被纳入候选链路”
+    ///
+    /// 这个方法不会占用 HalfOpen 探测名额，仅用于路由选择阶段的“可用性判断”：
+    /// - Closed / HalfOpen：可用（返回 true）
+    /// - Open：若超时到达则切到 HalfOpen 并返回 true，否则返回 false
+    ///
+    /// 注意：真正发起请求前仍需调用 `allow_request()` 来获取 HalfOpen 探测名额，
+    /// 并在请求结束后通过 `record_success()` / `record_failure()` 释放。
+    pub async fn is_available(&self) -> bool {
+        let state = *self.state.read().await;
+        let config = self.config.read().await;
+
+        match state {
+            CircuitState::Closed | CircuitState::HalfOpen => true,
+            CircuitState::Open => {
+                if let Some(opened_at) = *self.last_opened_at.read().await {
+                    if opened_at.elapsed().as_secs() >= config.timeout_seconds {
+                        drop(config); // 释放读锁再转换状态
+                        log::info!(
+                            "Circuit breaker transitioning from Open to HalfOpen (timeout reached)"
+                        );
+                        self.transition_to_half_open().await;
+                        return true;
+                    }
+                }
+                false
+            }
+        }
+    }
+
     /// 检查是否允许请求通过
     pub async fn allow_request(&self) -> bool {
         let state = *self.state.read().await;

src-tauri/src/proxy/forwarder.rs

@@ -148,13 +148,33 @@ impl RequestForwarder {
 
         let mut last_error = None;
         let mut failover_happened = false;
+        let mut attempted_providers = 0usize;
 
         // 依次尝试每个供应商
-        for (attempt, provider) in providers.iter().enumerate() {
+        for provider in providers.iter() {
+            // 发起请求前先获取熔断器放行许可（HalfOpen 会占用探测名额）
+            if !self
+                .router
+                .allow_provider_request(&provider.id, app_type_str)
+                .await
+            {
+                log::debug!(
+                    "[{}] Provider {} 熔断器拒绝本次请求，跳过",
+                    app_type_str,
+                    provider.name
+                );
+                continue;
+            }
+
+            attempted_providers += 1;
+            if attempted_providers > 1 {
+                failover_happened = true;
+            }
+
             log::info!(
                 "[{}] 尝试 {}/{} - 使用Provider: {} (sort_index: {})",
                 app_type_str,
-                attempt + 1,
+                attempted_providers,
                 providers.len(),
                 provider.name,
                 provider.sort_index.unwrap_or(999999)
@@ -167,9 +187,6 @@ impl RequestForwarder {
                 status.current_provider_id = Some(provider.id.clone());
                 status.total_requests += 1;
                 status.last_request_at = Some(chrono::Utc::now().to_rfc3339());
-                if attempt > 0 {
-                    failover_happened = true;
-                }
             }
 
             let start = Instant::now();
@@ -306,6 +323,21 @@ impl RequestForwarder {
             }
         }
 
+        if attempted_providers == 0 {
+            // providers 列表非空，但全部被熔断器拒绝（典型：HalfOpen 探测名额被占用）
+            {
+                let mut status = self.status.write().await;
+                status.failed_requests += 1;
+                status.last_error = Some("所有供应商暂时不可用（熔断器限制）".to_string());
+                if status.total_requests > 0 {
+                    status.success_rate = (status.success_requests as f32
+                        / status.total_requests as f32)
+                        * 100.0;
+                }
+            }
+            return Err(ProxyError::NoAvailableProvider);
+        }
+
         // 所有供应商都失败了
         {
             let mut status = self.status.write().await;

src-tauri/src/proxy/provider_router.rs

@@ -43,7 +43,7 @@ impl ProviderRouter {
                 let circuit_key = format!("{}:{}", app_type, current.id);
                 let breaker = self.get_or_create_circuit_breaker(&circuit_key).await;
 
-                if breaker.allow_request().await {
+                if breaker.is_available().await {
                     log::info!(
                         "[{}] Current provider available: {} ({})",
                         app_type,
@@ -81,7 +81,7 @@ impl ProviderRouter {
                 let circuit_key = format!("{}:{}", app_type, provider.id);
                 let breaker = self.get_or_create_circuit_breaker(&circuit_key).await;
 
-                if breaker.allow_request().await {
+                if breaker.is_available().await {
                     log::info!(
                         "[{}] Failover provider available: {} ({}) at queue position {}",
                         app_type,
@@ -116,6 +116,20 @@ impl ProviderRouter {
         Ok(result)
     }
 
+    /// 请求执行前获取熔断器“放行许可”
+    ///
+    /// - Closed：直接放行
+    /// - Open：超时到达后切到 HalfOpen 并放行一次探测
+    /// - HalfOpen：按限流规则放行探测
+    ///
+    /// 注意：调用方必须在请求结束后通过 `record_result()` 释放 HalfOpen 名额，
+    /// 否则会导致该 Provider 长时间无法进入探测状态。
+    pub async fn allow_provider_request(&self, provider_id: &str, app_type: &str) -> bool {
+        let circuit_key = format!("{app_type}:{provider_id}");
+        let breaker = self.get_or_create_circuit_breaker(&circuit_key).await;
+        breaker.allow_request().await
+    }
+
     /// 记录供应商请求结果
     pub async fn record_result(
         &self,
@@ -155,24 +169,6 @@ impl ProviderRouter {
             )
             .await?;
 
-        // 4. 如果连续失败达到熔断阈值，自动禁用代理目标
-        if !success {
-            let health = self.db.get_provider_health(provider_id, app_type).await?;
-
-            // 如果连续失败达到阈值，自动关闭该供应商的代理开关
-            if health.consecutive_failures >= failure_threshold {
-                log::warn!(
-                    "Provider {} has failed {} times (threshold: {}), auto-disabling proxy target",
-                    provider_id,
-                    health.consecutive_failures,
-                    failure_threshold
-                );
-                self.db
-                    .set_proxy_target(provider_id, app_type, false)
-                    .await?;
-            }
-        }
-
         Ok(())
     }
 
@@ -261,6 +257,7 @@ impl ProviderRouter {
 mod tests {
     use super::*;
     use crate::database::Database;
+    use serde_json::json;
 
     #[tokio::test]
     async fn test_provider_router_creation() {
@@ -271,4 +268,44 @@ mod tests {
         let breaker = router.get_or_create_circuit_breaker("claude:test").await;
         assert!(breaker.allow_request().await);
     }
+
+    #[tokio::test]
+    async fn select_providers_does_not_consume_half_open_permit() {
+        let db = Arc::new(Database::memory().unwrap());
+
+        // 配置：让熔断器 Open 后立刻进入 HalfOpen（timeout_seconds=0），并用 1 次失败就打开熔断器
+        db.update_circuit_breaker_config(&CircuitBreakerConfig {
+            failure_threshold: 1,
+            timeout_seconds: 0,
+            ..Default::default()
+        })
+        .await
+        .unwrap();
+
+        // 准备 2 个 Provider：A（当前）+ B（队列）
+        let provider_a =
+            Provider::with_id("a".to_string(), "Provider A".to_string(), json!({}), None);
+        let provider_b =
+            Provider::with_id("b".to_string(), "Provider B".to_string(), json!({}), None);
+
+        db.save_provider("claude", &provider_a).unwrap();
+        db.save_provider("claude", &provider_b).unwrap();
+        db.set_current_provider("claude", "a").unwrap();
+        db.add_to_failover_queue("claude", "b").unwrap();
+
+        let router = ProviderRouter::new(db.clone());
+
+        // 让 B 进入 Open 状态（failure_threshold=1）
+        router
+            .record_result("b", "claude", false, Some("fail".to_string()))
+            .await
+            .unwrap();
+
+        // select_providers 只做“可用性判断”，不应占用 HalfOpen 探测名额
+        let providers = router.select_providers("claude").await.unwrap();
+        assert_eq!(providers.len(), 2);
+
+        // 如果 select_providers 错误地消耗了 HalfOpen 名额，这里会返回 false（被限流拒绝）
+        assert!(router.allow_provider_request("b", "claude").await);
+    }
 }

src-tauri/src/proxy/providers/claude.rs

@@ -253,7 +253,6 @@ mod tests {
             meta: None,
             icon: None,
             icon_color: None,
-            is_proxy_target: None,
         }
     }
 

src-tauri/src/proxy/providers/codex.rs

@@ -174,7 +174,6 @@ mod tests {
             meta: None,
             icon: None,
             icon_color: None,
-            is_proxy_target: None,
         }
     }
 

src-tauri/src/proxy/providers/gemini.rs

@@ -250,7 +250,6 @@ mod tests {
             meta: None,
             icon: None,
             icon_color: None,
-            is_proxy_target: None,
         }
     }
 

src-tauri/src/proxy/providers/mod.rs

@@ -205,7 +205,6 @@ mod tests {
             meta: None,
             icon: None,
             icon_color: None,
-            is_proxy_target: None,
         }
     }
 

src-tauri/src/proxy/providers/transform.rs

@@ -394,7 +394,6 @@ mod tests {
             meta: None,
             icon: None,
             icon_color: None,
-            is_proxy_target: None,
         }
     }