fix(channel-monitor): build zhipu probe URL from the configured endpoint

The zhipu adapter always appended the official /api/paas/v4/chat/completions
path, so probes broke whenever the endpoint was not the official root:

- OpenAI-compatible relay (e.g. https://relay.example.com): requested
  /api/paas/v4/chat/completions, which relays do not serve -> 404
- Coding Plan base (https://open.bigmodel.cn/api/coding/paas/v4): produced
  .../coding/paas/v4/api/paas/v4/chat/completions -> 404

Resolve the path from the endpoint instead: append /chat/completions when it
already carries /paas/v4, keep the official path for bigmodel.cn / z.ai
roots, and fall back to /v1/chat/completions (same as kimi/deepseek/minimax)
for everything else.

Fixes #7067

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/internal/service/channel_monitor_checker.go

@@ -297,7 +297,7 @@ func callProvider(ctx context.Context, provider, endpoint, apiKey, model, prompt
 		return "", "", 0, err
 	}
 	headers := mergeHeaders(adapter.buildHeaders(apiKey), opts)
-	full := joinURL(endpoint, adapter.buildPath(model))
+	full := joinURL(endpoint, monitorRequestPath(provider, endpoint, adapter, model))
 	respBytes, status, err := postRawJSON(ctx, full, body, headers)
 	if err != nil {
 		return "", "", status, err
@@ -556,6 +556,37 @@ func postRawJSON(ctx context.Context, fullURL string, payload []byte, headers ma
 	return respBody, resp.StatusCode, nil
 }
 
+// monitorRequestPath 返回探测请求路径。智谱按 endpoint 区分：
+//   - 已带 /paas/v4（含 Coding Plan 的 /api/coding/paas/v4）：只追加 /chat/completions
+//   - 官方域名根地址：/api/paas/v4/chat/completions
+//   - 中转站 / 本站网关：只暴露 OpenAI 兼容的 /v1/chat/completions，与 Kimi / DeepSeek 一致
+func monitorRequestPath(provider, endpoint string, adapter providerAdapter, model string) string {
+	if provider != MonitorProviderZhipu {
+		return adapter.buildPath(model)
+	}
+	u, err := url.Parse(strings.TrimSpace(endpoint))
+	if err != nil {
+		return providerOpenAIPath
+	}
+	if strings.Contains(u.EscapedPath(), "/paas/v4") {
+		return "/chat/completions"
+	}
+	if isZhipuOfficialHost(u) {
+		return adapter.buildPath(model)
+	}
+	return providerOpenAIPath
+}
+
+func isZhipuOfficialHost(u *url.URL) bool {
+	host := strings.ToLower(u.Hostname())
+	for _, official := range []string{"bigmodel.cn", "z.ai"} {
+		if host == official || strings.HasSuffix(host, "."+official) {
+			return true
+		}
+	}
+	return false
+}
+
 // joinURL 保留 base 的上游路径前缀，并避免重复追加已有的 API 路径前缀。
 // 使用 EscapedPath 匹配完整路径段，避免把 hostname 或编码斜杠当作路径。
 func joinURL(base, path string) string {

backend/internal/service/channel_monitor_endpoint_test.go

@@ -84,6 +84,9 @@ func TestCallProvider_BasePath(t *testing.T) {
 		{"openai responses version", MonitorProviderOpenAI, MonitorAPIModeResponses, "/relay/v1", "/relay/v1/responses"},
 		{"gemini version", MonitorProviderGemini, "", "/relay/v1beta", "/relay/v1beta/models/test-model:generateContent"},
 		{"zhipu version", MonitorProviderZhipu, "", "/api/paas/v4", "/api/paas/v4/chat/completions"},
+		{"zhipu coding plan", MonitorProviderZhipu, "", "/api/coding/paas/v4", "/api/coding/paas/v4/chat/completions"},
+		{"zhipu relay origin", MonitorProviderZhipu, "", "", "/v1/chat/completions"},
+		{"zhipu relay version", MonitorProviderZhipu, "", "/relay/v1", "/relay/v1/chat/completions"},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
 			_, _, status, err := callProvider(context.Background(), tc.provider,
@@ -94,3 +97,19 @@ func TestCallProvider_BasePath(t *testing.T) {
 		})
 	}
 }
+
+func TestMonitorRequestPath_Zhipu(t *testing.T) {
+	adapter := providerAdapters[MonitorProviderZhipu]
+	for endpoint, want := range map[string]string{
+		"https://open.bigmodel.cn":                    providerZhipuPath,
+		"https://api.z.ai":                            providerZhipuPath,
+		"https://open.bigmodel.cn/api/coding/paas/v4": "/chat/completions",
+		"https://birdapi.up.railway.app":              providerOpenAIPath,
+		"https://notbigmodel.cn":                      providerOpenAIPath,
+		"https://relay.example.com/v1":                providerOpenAIPath,
+	} {
+		require.Equal(t, want, monitorRequestPath(MonitorProviderZhipu, endpoint, adapter, "glm-5.3-flash"), endpoint)
+	}
+	require.Equal(t, providerOpenAIPath,
+		monitorRequestPath(MonitorProviderDeepseek, "https://birdapi.up.railway.app", providerAdapters[MonitorProviderDeepseek], "m"))
+}