fix(proxy): fall back to OpenRouter for vendor-prefixed models (#1)

Author: mostlydev

internal/proxy/handler.go

@@ -128,8 +128,19 @@ func (h *Handler) handleOpenAI(w http.ResponseWriter, r *http.Request, agentID s
 
 	prov, err := h.registry.Get(providerName)
 	if err != nil {
-		h.fail(w, http.StatusBadGateway, "unknown provider", agentID, requestedModel, start, err)
-		return
+		// Compatibility: some clients targeting OpenRouter via an OpenAI-compatible
+		// provider config send vendor-prefixed model IDs like "anthropic/claude-*"
+		// instead of "openrouter/anthropic/claude-*". If no first-party provider is
+		// configured for that prefix, route through OpenRouter and preserve the full
+		// vendor/model path as the upstream model.
+		bridge, bridgeErr := h.registry.Get("openrouter")
+		if bridgeErr != nil || strings.EqualFold(providerName, "openrouter") {
+			h.fail(w, http.StatusBadGateway, "unknown provider", agentID, requestedModel, start, err)
+			return
+		}
+		upstreamModel = providerName + "/" + upstreamModel
+		providerName = bridge.Name
+		prov = bridge
 	}
 
 	// Format bridge: if the resolved provider uses Anthropic format but

internal/proxy/handler_test.go

@@ -85,6 +85,50 @@ func TestHandlerRejectsUnknownProvider(t *testing.T) {
 	}
 }
 
+func TestHandlerFallsBackToOpenRouterForVendorPrefixedModel(t *testing.T) {
+	var gotAuth string
+	var gotBody []byte
+	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotAuth = r.Header.Get("Authorization")
+		var err error
+		gotBody, err = io.ReadAll(r.Body)
+		if err != nil {
+			t.Fatalf("read body: %v", err)
+		}
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"id":"chatcmpl-1","choices":[{"message":{"content":"hello"}}]}`))
+	}))
+	defer backend.Close()
+
+	reg := provider.NewRegistry("")
+	reg.Set("openrouter", &provider.Provider{
+		Name: "openrouter", BaseURL: backend.URL + "/v1", APIKey: "sk-real", Auth: "bearer",
+	})
+
+	h := NewHandler(reg, stubContextLoaderWithToken("tiverton", "tiverton:dummy123"), nil)
+	body := `{"model":"anthropic/claude-sonnet-4","messages":[{"role":"user","content":"hi"}]}`
+	req := httptest.NewRequest(http.MethodPost, "/v1/chat/completions", bytes.NewBufferString(body))
+	req.Header.Set("Authorization", "Bearer tiverton:dummy123")
+	req.Header.Set("Content-Type", "application/json")
+	w := httptest.NewRecorder()
+
+	h.ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200, got %d: %s", w.Code, w.Body.String())
+	}
+	if gotAuth != "Bearer sk-real" {
+		t.Fatalf("expected openrouter auth forwarded, got %q", gotAuth)
+	}
+	var payload map[string]any
+	if err := json.Unmarshal(gotBody, &payload); err != nil {
+		t.Fatalf("unmarshal backend body: %v", err)
+	}
+	if payload["model"] != "anthropic/claude-sonnet-4" {
+		t.Fatalf("expected vendor-prefixed model preserved for openrouter fallback, got %#v", payload["model"])
+	}
+}
+
 func TestHandlerRejectsWrongSecret(t *testing.T) {
 	reg := provider.NewRegistry("")
 	reg.Set("openai", &provider.Provider{Name: "openai", BaseURL: "https://api.openai.com/v1", APIKey: "sk-real", Auth: "bearer"})