proxy: add versionless API endpoint (#733)

Add versionless endpoints under v/ to support upstream peers that 
do not use the v1/ prefix.

Fixes #728.

proxy/proxymanager_test.go

@@ -1779,3 +1779,103 @@ models:
 	assert.Nil(t, capture.ReqBody)
 	assert.NotNil(t, capture.RespBody)
 }
+
+func TestProxyManager_VersionlessEndpoints_LocalModel(t *testing.T) {
+	cfg := testConfigFromYAML(t, `
+healthCheckTimeout: 15
+logLevel: error
+models:
+  model1:
+    cmd: {{RESPONDER}} --port ${PORT} --silent --respond model1
+`)
+
+	proxy := New(cfg)
+	defer proxy.StopProcesses(StopWaitForInflightRequest)
+	injectTestHandlers(proxy, nil)
+
+	endpoints := []string{
+		"/v/chat/completions",
+		"/v/responses",
+		"/v/completions",
+		"/v/embeddings",
+		"/v/rerank",
+		"/v/reranking",
+	}
+
+	for _, endpoint := range endpoints {
+		t.Run(endpoint, func(t *testing.T) {
+			reqBody := `{"model":"model1"}`
+			req := httptest.NewRequest("POST", endpoint, bytes.NewBufferString(reqBody))
+			w := CreateTestResponseRecorder()
+			proxy.ServeHTTP(w, req)
+			assert.Equal(t, http.StatusOK, w.Code)
+			assert.Contains(t, w.Body.String(), "model1")
+		})
+	}
+
+	t.Run("/v/messages", func(t *testing.T) {
+		reqBody := `{"model":"model1","messages":[{"role":"user","content":"hi"}]}`
+		req := httptest.NewRequest("POST", "/v/messages", bytes.NewBufferString(reqBody))
+		w := CreateTestResponseRecorder()
+		proxy.ServeHTTP(w, req)
+		assert.Equal(t, http.StatusOK, w.Code)
+		assert.Contains(t, w.Body.String(), "model1")
+	})
+}
+
+func TestProxyManager_VersionlessEndpoints_PeerModel(t *testing.T) {
+	peerServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusOK)
+		fmt.Fprintf(w, `{"endpoint":"%s","model":"peer-model"}`, r.URL.Path)
+	}))
+	defer peerServer.Close()
+
+	cfg := testConfigFromYAML(t, fmt.Sprintf(`
+healthCheckTimeout: 15
+logLevel: error
+peers:
+  test-peer:
+    proxy: %s
+    models:
+      - peer-model
+models:
+  local-model:
+    cmd: {{RESPONDER}} --port ${PORT} --silent --respond local-model
+`, peerServer.URL))
+
+	proxy := New(cfg)
+	defer proxy.StopProcesses(StopImmediately)
+
+	endpoints := []struct {
+		path       string
+		wantSuffix string
+	}{
+		{"/v/chat/completions", "/chat/completions"},
+		{"/v/responses", "/responses"},
+		{"/v/completions", "/completions"},
+		{"/v/embeddings", "/embeddings"},
+		{"/v/rerank", "/rerank"},
+		{"/v/reranking", "/reranking"},
+	}
+
+	for _, ep := range endpoints {
+		t.Run(ep.path, func(t *testing.T) {
+			reqBody := `{"model":"peer-model"}`
+			req := httptest.NewRequest("POST", ep.path, bytes.NewBufferString(reqBody))
+			w := CreateTestResponseRecorder()
+			proxy.ServeHTTP(w, req)
+			assert.Equal(t, http.StatusOK, w.Code)
+			assert.Contains(t, w.Body.String(), ep.wantSuffix)
+		})
+	}
+
+	t.Run("/v/messages", func(t *testing.T) {
+		reqBody := `{"model":"peer-model","messages":[{"role":"user","content":"hi"}]}`
+		req := httptest.NewRequest("POST", "/v/messages", bytes.NewBufferString(reqBody))
+		w := CreateTestResponseRecorder()
+		proxy.ServeHTTP(w, req)
+		assert.Equal(t, http.StatusOK, w.Code)
+		assert.Contains(t, w.Body.String(), "/messages")
+	})
+}