feat(web,api): add test connection with real connectivity verification

Split from PR #2752 (part 3 of 3).

Backend:
- /api/models/{index}/test endpoint for testing saved model configs
- /api/models/test-inline endpoint for testing unsaved form values
- Real network probe (GET /models) for connectivity verification
- Credential reuse with provider/API base matching for security
- Default API base resolution for providers without explicit base

Frontend:
- TestModelDialog for testing model connectivity
- Inline test support for add/edit model sheets
- Static import for TestModelDialog (replaces dynamic import from PR1)

web/backend/api/models.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"net/url"
 	"strconv"
 	"strings"
 	"sync"
@@ -39,6 +40,8 @@ func (h *Handler) registerModelRoutes(mux *http.ServeMux) {
 	mux.HandleFunc("POST /api/models/fetch", h.handleFetchModels)
 	mux.HandleFunc("GET /api/models/catalog", h.handleListCatalogs)
 	mux.HandleFunc("DELETE /api/models/catalog/{id}", h.handleDeleteCatalog)
+	mux.HandleFunc("POST /api/models/{index}/test", h.handleTestModel)
+	mux.HandleFunc("POST /api/models/test-inline", h.handleTestInlineModel)
 }
 
 // modelResponse is the JSON structure returned for each model in the list.
@@ -800,3 +803,194 @@ func fetchOllamaModels(ctx context.Context, fetchURL string) ([]upstreamModel, e
 	}
 	return models, nil
 }
+
+// normalizeAPIBaseForCompare normalizes an API base URL for equality comparison
+// by trimming trailing slashes and lowering the scheme/host.
+func normalizeAPIBaseForCompare(raw string) string {
+	raw = strings.TrimSpace(raw)
+	if raw == "" {
+		return ""
+	}
+	raw = strings.TrimRight(raw, "/")
+	u, err := url.Parse(raw)
+	if err != nil {
+		return strings.ToLower(raw)
+	}
+	if u.Host == "" {
+		u, err = url.Parse("//" + raw)
+		if err != nil {
+			return strings.ToLower(raw)
+		}
+	}
+	return strings.ToLower(u.Scheme) + "://" + strings.ToLower(u.Host) + strings.TrimRight(u.Path, "/")
+}
+
+// handleTestModel tests connectivity to a model endpoint.
+//
+//	POST /api/models/{index}/test
+func (h *Handler) handleTestModel(w http.ResponseWriter, r *http.Request) {
+	idx, err := strconv.Atoi(r.PathValue("index"))
+	if err != nil {
+		http.Error(w, "Invalid index", http.StatusBadRequest)
+		return
+	}
+
+	cfg, err := config.LoadConfig(h.configPath)
+	if err != nil {
+		http.Error(w, fmt.Sprintf("Failed to load config: %v", err), http.StatusInternalServerError)
+		return
+	}
+
+	if idx < 0 || idx >= len(cfg.ModelList) {
+		http.Error(w, fmt.Sprintf("Index %d out of range (0-%d)", idx, len(cfg.ModelList)-1), http.StatusNotFound)
+		return
+	}
+
+	m := cfg.ModelList[idx]
+	start := time.Now()
+	summary := modelConfigurationStatus(m)
+	latency := time.Since(start).Milliseconds()
+
+	result := map[string]any{
+		"success":    summary.Available,
+		"latency_ms": latency,
+		"status":     summary.Status,
+	}
+
+	if !summary.Available {
+		if summary.Status == modelStatusUnconfigured {
+			result["error"] = "API key not configured"
+		} else {
+			result["error"] = "Endpoint unreachable"
+		}
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(result)
+}
+
+// handleTestInlineModel tests connectivity using inline (unsaved) parameters.
+// Unlike handleTestModel which only checks saved config, this endpoint performs
+// a real network probe (e.g. GET /models) to verify the endpoint is reachable.
+//
+//	POST /api/models/test-inline
+func (h *Handler) handleTestInlineModel(w http.ResponseWriter, r *http.Request) {
+	body, err := io.ReadAll(io.LimitReader(r.Body, 1<<20))
+	if err != nil {
+		http.Error(w, "Failed to read request body", http.StatusBadRequest)
+		return
+	}
+
+	var req struct {
+		Provider   string `json:"provider"`
+		Model      string `json:"model"`
+		APIBase    string `json:"api_base"`
+		APIKey     string `json:"api_key"`
+		AuthMethod string `json:"auth_method"`
+		ModelIndex *int   `json:"model_index"`
+	}
+	if err := json.Unmarshal(body, &req); err != nil {
+		http.Error(w, "Invalid JSON", http.StatusBadRequest)
+		return
+	}
+
+	m := &config.ModelConfig{
+		Provider:   strings.TrimSpace(req.Provider),
+		Model:      strings.TrimSpace(req.Model),
+		APIBase:    strings.TrimSpace(req.APIBase),
+		AuthMethod: strings.TrimSpace(req.AuthMethod),
+	}
+	if req.APIKey != "" {
+		m.SetAPIKey(req.APIKey)
+	}
+
+	// When api_key is empty and model_index is provided, fall back to stored credentials.
+	// This lets the edit form test unsaved field changes while using the saved key.
+	// Only reuse the stored key when the provider and effective API base match
+	// the saved model, to prevent attaching a credential to a different endpoint.
+	if req.APIKey == "" && req.ModelIndex != nil {
+		cfg, err := config.LoadConfig(h.configPath)
+		if err == nil && *req.ModelIndex >= 0 && *req.ModelIndex < len(cfg.ModelList) {
+			stored := cfg.ModelList[*req.ModelIndex]
+			storedProvider, _ := providers.ExtractProtocol(stored)
+			reqProvider := providers.NormalizeProvider(m.Provider)
+			providerMatch := reqProvider == "" || reqProvider == providers.NormalizeProvider(storedProvider)
+
+			effectiveReqBase := strings.TrimSpace(m.APIBase)
+			if effectiveReqBase == "" {
+				effectiveReqBase = providers.DefaultAPIBaseForProtocol(reqProvider)
+			}
+			effectiveStoredBase := strings.TrimSpace(stored.APIBase)
+			if effectiveStoredBase == "" {
+				effectiveStoredBase = providers.DefaultAPIBaseForProtocol(storedProvider)
+			}
+			baseMatch := normalizeAPIBaseForCompare(effectiveReqBase) == normalizeAPIBaseForCompare(effectiveStoredBase)
+
+			if providerMatch && baseMatch {
+				if stored.APIKey() != "" {
+					m.SetAPIKey(stored.APIKey())
+				}
+				if m.APIBase == "" && stored.APIBase != "" {
+					m.APIBase = stored.APIBase
+				}
+			}
+		}
+	}
+
+	// Check if configuration exists
+	if !hasModelConfiguration(m) {
+		w.Header().Set("Content-Type", "application/json")
+		json.NewEncoder(w).Encode(map[string]any{
+			"success":    false,
+			"latency_ms": 0,
+			"status":     modelStatusUnconfigured,
+			"error":      "API key not configured",
+		})
+		return
+	}
+
+	// Perform a real network probe
+	start := time.Now()
+	available := probeModelConnectivity(m)
+	latency := time.Since(start).Milliseconds()
+
+	result := map[string]any{
+		"success":    available,
+		"latency_ms": latency,
+	}
+	if available {
+		result["status"] = modelStatusAvailable
+	} else {
+		result["status"] = modelStatusUnreachable
+		result["error"] = "Endpoint unreachable"
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(result)
+}
+
+// probeModelConnectivity performs a real network probe to verify model endpoint reachability.
+func probeModelConnectivity(m *config.ModelConfig) bool {
+	apiBase := modelProbeAPIBase(m)
+	protocol, modelID := splitModel(m)
+
+	switch protocol {
+	case "ollama":
+		return probeOllamaModel(apiBase, modelID)
+	case "vllm", "lmstudio":
+		return probeOpenAICompatibleModel(apiBase, modelID, m.APIKey())
+	case "github-copilot", "copilot":
+		return probeTCPService(apiBase)
+	case "claude-cli", "claudecli":
+		return probeCommandAvailable("claude")
+	case "codex-cli", "codexcli":
+		return probeCommandAvailable("codex")
+	default:
+		// For remote providers (OpenAI, Anthropic, Gemini, DeepSeek, etc.),
+		// make a real GET /models request to verify connectivity and credentials.
+		if apiBase != "" {
+			return probeOpenAICompatibleModel(apiBase, modelID, m.APIKey())
+		}
+		return false
+	}
+}

web/frontend/src/components/models/add-model-sheet.tsx

@@ -40,6 +40,7 @@ import { type FieldValidation, validateModelField } from "./model-validation"
 import { ProviderCombobox } from "./provider-combobox"
 import { getProviderKey } from "./provider-label"
 import { FETCHABLE_PROVIDER_KEYS, PROVIDER_MAP } from "./provider-registry"
+import { TestModelDialog } from "./test-model-dialog"
 
 interface AddForm {
   modelName: string
@@ -142,15 +143,6 @@ export function AddModelSheet({
   const debounceRef = useRef<ReturnType<typeof setTimeout>>(undefined)
   const scrollContainerRef = useRef<HTMLDivElement>(null)
 
-  // Dynamic import for TestModelDialog (added in PR3)
-  const [TestModelDialogComp, setTestModelDialogComp] = useState<React.ComponentType<{
-    model: unknown; open: boolean; onClose: () => void;
-    inlineParams: { provider: string; model: string; apiBase: string; apiKey: string; authMethod: string };
-  }> | null>(null)
-  useEffect(() => {
-    import("./test-model-dialog").then((m) => setTestModelDialogComp(() => m.TestModelDialog)).catch(() => {})
-  }, [])
-
   const apiKeyPlaceholder = maskedSecretPlaceholder(
     form.apiKey,
     t("models.field.apiKeyPlaceholder"),
@@ -556,7 +548,7 @@ export function AddModelSheet({
                   variant="outline"
                   size="sm"
                   onClick={() => setTestOpen(true)}
-                  disabled={!form.provider || !form.model || !TestModelDialogComp}
+                  disabled={!form.provider || !form.model}
                 >
                   <IconPlugConnected className="size-4" />
                   {t("models.test.testConnection")}
@@ -744,20 +736,18 @@ export function AddModelSheet({
           apiBase={form.apiBase}
         />
 
-        {TestModelDialogComp && (
+        <TestModelDialog
-          <TestModelDialogComp
+          model={null}
-            model={null}
+          open={testOpen}
-            open={testOpen}
+          onClose={() => setTestOpen(false)}
-            onClose={() => setTestOpen(false)}
+          inlineParams={{
-            inlineParams={{
+            provider: form.provider,
-              provider: form.provider,
+            model: form.model,
-              model: form.model,
+            apiBase: form.apiBase,
-              apiBase: form.apiBase,
+            apiKey: form.apiKey,
-              apiKey: form.apiKey,
+            authMethod: form.authMethod,
-              authMethod: form.authMethod,
+          }}
-            }}
+        />
-          />
-        )}
       </Sheet>
     </>
   )

web/frontend/src/components/models/edit-model-sheet.tsx

@@ -41,6 +41,7 @@ import { type FieldValidation, validateModelField } from "./model-validation"
 import { ProviderCombobox } from "./provider-combobox"
 import { getProviderKey } from "./provider-label"
 import { FETCHABLE_PROVIDER_KEYS, PROVIDER_API_BASES, PROVIDER_MAP } from "./provider-registry"
+import { TestModelDialog } from "./test-model-dialog"
 
 interface EditForm {
   provider: string
@@ -159,15 +160,6 @@ export function EditModelSheet({
   const debounceRef = useRef<ReturnType<typeof setTimeout>>(undefined)
   const scrollContainerRef = useRef<HTMLDivElement>(null)
 
-  // Dynamic import for TestModelDialog (added in PR3)
-  const [TestModelDialogComp, setTestModelDialogComp] = useState<React.ComponentType<{
-    model: unknown; open: boolean; onClose: () => void;
-    inlineParams: { provider: string; model: string; apiBase: string; apiKey: string; authMethod: string; modelIndex?: number };
-  }> | null>(null)
-  useEffect(() => {
-    import("./test-model-dialog").then((m) => setTestModelDialogComp(() => m.TestModelDialog)).catch(() => {})
-  }, [])
-
   const initialForm = model ? buildInitialEditForm(model) : null
   const isDirty =
     model != null &&
@@ -513,7 +505,7 @@ export function EditModelSheet({
                   variant="outline"
                   size="sm"
                   onClick={() => setTestOpen(true)}
-                  disabled={!model || !TestModelDialogComp}
+                  disabled={!model}
                 >
                   <IconPlugConnected className="size-4" />
                   {t("models.test.testConnection")}
@@ -693,21 +685,19 @@ export function EditModelSheet({
         </SheetContent>
       </Sheet>
 
-      {TestModelDialogComp && (
+      <TestModelDialog
-        <TestModelDialogComp
+        model={model}
-          model={model}
+        open={testOpen}
-          open={testOpen}
+        onClose={() => setTestOpen(false)}
-          onClose={() => setTestOpen(false)}
+        inlineParams={{
-          inlineParams={{
+          provider: form.provider,
-            provider: form.provider,
+          model: form.modelId,
-            model: form.modelId,
+          apiBase: form.apiBase,
-            apiBase: form.apiBase,
+          apiKey: form.apiKey,
-            apiKey: form.apiKey,
+          authMethod: form.authMethod,
-            authMethod: form.authMethod,
+          modelIndex: model?.index,
-            modelIndex: model?.index,
+        }}
-          }}
+      />
-        />
-      )}
 
       <FetchModelsDialog
         open={fetchOpen}

web/frontend/src/components/models/test-model-dialog.tsx

@@ -1,4 +1,195 @@
-// Placeholder: full implementation added in PR3 (Test Connection)
+import { IconLoader2, IconPlugConnected, IconX } from "@tabler/icons-react"
-export function TestModelDialog() {
+import { useState } from "react"
-  return null
+import { useTranslation } from "react-i18next"
+
+import {
+  type ModelInfo,
+  type TestModelInlineRequest,
+  testModel,
+  testModelInline,
+} from "@/api/models"
+import { Button } from "@/components/ui/button"
+import {
+  Dialog,
+  DialogContent,
+  DialogDescription,
+  DialogFooter,
+  DialogHeader,
+  DialogTitle,
+} from "@/components/ui/dialog"
+
+export interface TestInlineParams {
+  provider: string
+  model: string
+  apiBase: string
+  apiKey: string
+  authMethod: string
+  modelIndex?: number
+}
+
+interface TestModelDialogProps {
+  model: ModelInfo | null
+  open: boolean
+  onClose: () => void
+  inlineParams?: TestInlineParams
+}
+
+interface TestResult {
+  success: boolean
+  latency_ms: number
+  status: string
+  error?: string
+}
+
+export function TestModelDialog({
+  model,
+  open,
+  onClose,
+  inlineParams,
+}: TestModelDialogProps) {
+  const { t } = useTranslation()
+  const [testing, setTesting] = useState(false)
+  const [result, setResult] = useState<TestResult | null>(null)
+
+  const handleTest = async () => {
+    setTesting(true)
+    setResult(null)
+    try {
+      let res: TestResult
+      if (inlineParams) {
+        const req: TestModelInlineRequest = {
+          provider: inlineParams.provider,
+          model: inlineParams.model,
+          api_base: inlineParams.apiBase || undefined,
+          api_key: inlineParams.apiKey || undefined,
+          auth_method: inlineParams.authMethod || undefined,
+          model_index: inlineParams.modelIndex,
+        }
+        res = await testModelInline(req)
+      } else if (model) {
+        res = await testModel(model.index)
+      } else {
+        return
+      }
+      setResult(res)
+    } catch (e) {
+      setResult({
+        success: false,
+        latency_ms: 0,
+        status: "error",
+        error: e instanceof Error ? e.message : t("models.test.testFailed"),
+      })
+    } finally {
+      setTesting(false)
+    }
+  }
+
+  const handleClose = () => {
+    setResult(null)
+    onClose()
+  }
+
+  // Display info: prefer inline params, fall back to saved model
+  const displayModelName = inlineParams?.model || model?.model_name || ""
+  const displayModel = inlineParams?.model || model?.model || ""
+  const displayApiBase = inlineParams?.apiBase || model?.api_base || ""
+  const canTest = !!(inlineParams || model)
+
+  return (
+    <Dialog open={open} onOpenChange={(v) => !v && handleClose()}>
+      <DialogContent className="sm:max-w-md">
+        <DialogHeader>
+          <DialogTitle className="flex items-center gap-2">
+            <IconPlugConnected className="size-5" />
+            {t("models.test.title")}
+          </DialogTitle>
+          <DialogDescription>{t("models.test.description")}</DialogDescription>
+        </DialogHeader>
+
+        {canTest && (
+          <div className="space-y-3">
+            <div className="bg-muted/50 rounded-lg p-3 text-sm">
+              <div>
+                <span className="text-muted-foreground">
+                  {t("models.test.modelLabel")}{" "}
+                </span>
+                <span className="font-mono">{displayModelName}</span>
+              </div>
+              <div>
+                <span className="text-muted-foreground">
+                  {t("models.test.identifierLabel")}{" "}
+                </span>
+                <span className="font-mono">{displayModel}</span>
+              </div>
+              {displayApiBase && (
+                <div>
+                  <span className="text-muted-foreground">
+                    {t("models.test.endpointLabel")}{" "}
+                  </span>
+                  <span className="font-mono text-xs">{displayApiBase}</span>
+                </div>
+              )}
+            </div>
+
+            {!result && !testing && (
+              <Button onClick={handleTest} className="w-full">
+                <IconPlugConnected className="size-4" />
+                {t("models.test.testConnection")}
+              </Button>
+            )}
+
+            {testing && (
+              <div className="text-muted-foreground flex items-center justify-center gap-2 py-6">
+                <IconLoader2 className="size-5 animate-spin" />
+                <span>{t("models.test.testing")}</span>
+              </div>
+            )}
+
+            {result && (
+              <div
+                className={`rounded-lg p-4 text-sm ${
+                  result.success
+                    ? "bg-green-500/10 text-green-700 dark:text-green-400"
+                    : "bg-destructive/10 text-destructive"
+                }`}
+              >
+                {result.success ? (
+                  <div className="space-y-1">
+                    <div className="font-medium">
+                      {t("models.test.success")}
+                    </div>
+                    <div className="text-xs opacity-80">
+                      {t("models.test.responseTime", { ms: result.latency_ms })}
+                    </div>
+                  </div>
+                ) : (
+                  <div className="space-y-1">
+                    <div className="flex items-center gap-1 font-medium">
+                      <IconX className="size-4" />
+                      {t("models.test.failed")}
+                    </div>
+                    <div className="text-xs opacity-80">
+                      {result.error ||
+                        t("models.test.status", { status: result.status })}
+                    </div>
+                  </div>
+                )}
+              </div>
+            )}
+          </div>
+        )}
+
+        <DialogFooter>
+          <Button variant="ghost" onClick={handleClose}>
+            {t("common.cancel")}
+          </Button>
+          {result && (
+            <Button variant="outline" onClick={handleTest}>
+              {t("models.test.testAgain")}
+            </Button>
+          )}
+        </DialogFooter>
+      </DialogContent>
+    </Dialog>
+  )
 }