fix(ai): stop forcing Foundry v1 from hostname; retry classic chat on 404

Helix Chat 404 DeploymentNotFound after #118 because every
*.services.ai.azure.com host was routed to /openai/v1/chat/completions
without api-version. Restore flavor deployments URLs unless the path
explicitly contains /openai/v1, and fall back to that classic URL when
v1 chat 404s.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 5b104204-65b7-4d04-90a4-e2d5897b8e2e

Author: atulmgupta

internal/ai/provider/azure/azure.go

@@ -176,7 +176,17 @@ func (a *Adapter) Chat(ctx context.Context, req provider.ChatRequest) (*provider
 	defer resp.Body.Close()
 	if resp.StatusCode/100 != 2 {
 		raw, _ := io.ReadAll(io.LimitReader(resp.Body, 4096))
-		return nil, fmt.Errorf("%w: azure chat status %d: %s", provider.ErrUpstream, resp.StatusCode, string(raw))
+		chatErr := fmt.Errorf("%w: azure chat status %d: %s", provider.ErrUpstream, resp.StatusCode, string(raw))
+		// Foundry portal endpoints often include /openai/v1, but
+		// gpt-5.x deployments 404 on that chat/completions surface.
+		// Retry the pre-#118 flavor URL (deployments or Foundry
+		// inference) after stripping /openai/v1.
+		if resp.StatusCode == http.StatusNotFound && a.usesOpenAIV1() {
+			if fallback, ferr := a.withoutOpenAIV1().Chat(ctx, req); ferr == nil {
+				return fallback, nil
+			}
+		}
+		return nil, chatErr
 	}
 	var wire azureChatResponse
 	if err := json.NewDecoder(resp.Body).Decode(&wire); err != nil {
@@ -413,25 +423,48 @@ func (a *Adapter) embedURL(identity string) (string, error) {
 }
 
 // isAzureOpenAIV1 reports whether baseURL is Azure AI Foundry's
-// OpenAI-compatible v1 surface. Detected from:
-//   - path containing /openai/v1 (the portal "endpoint" field)
-//   - host *.services.ai.azure.com (Foundry AI Services resource)
+// OpenAI-compatible v1 surface. Only the path is authoritative —
+// hostname *.services.ai.azure.com also hosts classic
+// /openai/deployments/{name}/chat/completions?api-version= which
+// Helix used successfully before auto-detect (#118) forced v1.
 func isAzureOpenAIV1(baseURL string) bool {
 	u, err := url.Parse(strings.TrimSpace(baseURL))
 	if err != nil {
 		return false
 	}
 	p := strings.ToLower(path.Clean(u.Path))
-	if strings.Contains(p, "/openai/v1") {
-		return true
-	}
-	return strings.Contains(strings.ToLower(u.Hostname()), "services.ai.azure.com")
+	return strings.Contains(p, "/openai/v1")
 }
 
 func (a *Adapter) usesOpenAIV1() bool {
 	return isAzureOpenAIV1(a.cfg.BaseURL)
 }
 
+func stripOpenAIV1Path(baseURL string) string {
+	u, err := url.Parse(strings.TrimSpace(baseURL))
+	if err != nil {
+		return strings.TrimSpace(baseURL)
+	}
+	cleaned := path.Clean(u.Path)
+	lower := strings.ToLower(cleaned)
+	if i := strings.Index(lower, "/openai/v1"); i >= 0 {
+		cleaned = cleaned[:i]
+		if cleaned == "" {
+			cleaned = "/"
+		}
+		u.Path = cleaned
+	}
+	u.RawQuery = ""
+	u.Fragment = ""
+	return strings.TrimRight(u.String(), "/")
+}
+
+func (a *Adapter) withoutOpenAIV1() *Adapter {
+	clone := *a
+	clone.cfg.BaseURL = stripOpenAIV1Path(a.cfg.BaseURL)
+	return &clone
+}
+
 // buildOpenAIV1URL joins BaseURL (ensuring /openai/v1) with extra
 // segments and omits api-version. Foundry's v1 GA API 404s when the
 // classic Azure OpenAI api-version (2024-10-21) is attached.

internal/ai/provider/azure/azure_test.go

@@ -602,7 +602,7 @@ func TestIsAzureOpenAIV1(t *testing.T) {
 		want bool
 	}{
 		{"https://my-resource.services.ai.azure.com/openai/v1", true},
-		{"https://my-resource.services.ai.azure.com", true},
+		{"https://my-resource.services.ai.azure.com", false},
 		{"https://my-resource.openai.azure.com/openai/v1", true},
 		{"https://my-resource.openai.azure.com", false},
 		{"http://127.0.0.1:1234", false},
@@ -614,7 +614,7 @@ func TestIsAzureOpenAIV1(t *testing.T) {
 	}
 }
 
-func TestChatEndpoint_V1ServicesHost(t *testing.T) {
+func TestChatEndpoint_ServicesHostUsesClassicOpenAI(t *testing.T) {
 	t.Parallel()
 	a, err := New(provider.ProviderConfig{
 		BaseURL:    "https://my-resource.services.ai.azure.com",
@@ -630,11 +630,14 @@ func TestChatEndpoint_V1ServicesHost(t *testing.T) {
 	if err != nil {
 		t.Fatalf("chatEndpoint: %v", err)
 	}
-	if model != "gpt-5.6-sol" {
-		t.Errorf("modelInBody=%q", model)
+	if model != "" {
+		t.Errorf("modelInBody=%q, want empty (deployment in URL)", model)
 	}
-	if u != "https://my-resource.services.ai.azure.com/openai/v1/chat/completions" {
-		t.Errorf("url=%s", u)
+	if !strings.Contains(u, "/openai/deployments/gpt-5.6-sol/chat/completions") {
+		t.Errorf("url=%s, want classic deployments path", u)
+	}
+	if !strings.Contains(u, "api-version=2024-10-21") {
+		t.Errorf("url=%s, want api-version", u)
 	}
 }
 
@@ -764,3 +767,49 @@ func TestOpenAIV1_Chat_URLAuthAndBody(t *testing.T) {
 		t.Fatalf("content=%q", resp.Message.Content)
 	}
 }
+
+func TestChat_V1NotFoundFallsBackToDeployments(t *testing.T) {
+	t.Parallel()
+	var v1Hits, deployHits int
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if strings.Contains(r.URL.Path, "/openai/v1/") {
+			v1Hits++
+			w.WriteHeader(http.StatusNotFound)
+			_, _ = io.WriteString(w, `{ "error": { "code": "DeploymentNotFound" } }`)
+			return
+		}
+		if !strings.Contains(r.URL.Path, "/openai/deployments/gpt-5.6-sol/chat/completions") {
+			t.Errorf("unexpected path=%s", r.URL.Path)
+			w.WriteHeader(http.StatusNotFound)
+			return
+		}
+		if r.URL.Query().Get("api-version") == "" {
+			t.Errorf("missing api-version on %s", r.URL.String())
+		}
+		deployHits++
+		_, _ = io.WriteString(w, `{"choices":[{"index":0,"finish_reason":"stop","message":{"role":"assistant","content":"classic"}}]}`)
+	}))
+	t.Cleanup(srv.Close)
+	a, err := New(provider.ProviderConfig{
+		BaseURL:    srv.URL + "/openai/v1",
+		Model:      "gpt-5.6-sol",
+		APIKey:     "k",
+		APIVersion: "2024-10-21",
+		Flavor:     provider.AzureFlavorOpenAI,
+	}, WithHTTPClient(srv.Client()))
+	if err != nil {
+		t.Fatalf("New: %v", err)
+	}
+	resp, err := a.Chat(context.Background(), provider.ChatRequest{
+		Messages: []provider.Message{{Role: provider.RoleUser, Content: "ping"}},
+	})
+	if err != nil {
+		t.Fatalf("Chat: %v", err)
+	}
+	if resp.Message.Content != "classic" {
+		t.Fatalf("content=%q", resp.Message.Content)
+	}
+	if v1Hits != 1 || deployHits != 1 {
+		t.Fatalf("hits v1=%d deploy=%d", v1Hits, deployHits)
+	}
+}