feat: add openai-compatible endpoint support for google-vertex provider (#10303)

Co-authored-by: BlueT - Matthew Lien - 練喆明 <BlueT@BlueT.org>
Co-authored-by: Aiden Cline <63023139+rekram1-node@users.noreply.github.com>
Co-authored-by: Aiden Cline <aidenpcline@gmail.com>

packages/opencode/test/provider/provider.test.ts

@@ -2127,3 +2127,95 @@ test("custom model with variants enabled and disabled", async () => {
     },
   })
 })
+
+test("Google Vertex: retains baseURL for custom proxy", async () => {
+  await using tmp = await tmpdir({
+    init: async (dir) => {
+      await Bun.write(
+        path.join(dir, "opencode.json"),
+        JSON.stringify({
+          $schema: "https://opencode.ai/config.json",
+          provider: {
+            "vertex-proxy": {
+              name: "Vertex Proxy",
+              npm: "@ai-sdk/google-vertex",
+              api: "https://my-proxy.com/v1",
+              env: ["GOOGLE_APPLICATION_CREDENTIALS"], // Mock env var requirement
+              models: {
+                "gemini-pro": {
+                  name: "Gemini Pro",
+                  tool_call: true,
+                },
+              },
+              options: {
+                project: "test-project",
+                location: "us-central1",
+                baseURL: "https://my-proxy.com/v1", // Should be retained
+              },
+            },
+          },
+        }),
+      )
+    },
+  })
+
+  await Instance.provide({
+    directory: tmp.path,
+    init: async () => {
+      Env.set("GOOGLE_APPLICATION_CREDENTIALS", "test-creds")
+    },
+    fn: async () => {
+      const providers = await Provider.list()
+      expect(providers["vertex-proxy"]).toBeDefined()
+      expect(providers["vertex-proxy"].options.baseURL).toBe("https://my-proxy.com/v1")
+    },
+  })
+})
+
+test("Google Vertex: supports OpenAI compatible models", async () => {
+  await using tmp = await tmpdir({
+    init: async (dir) => {
+      await Bun.write(
+        path.join(dir, "opencode.json"),
+        JSON.stringify({
+          $schema: "https://opencode.ai/config.json",
+          provider: {
+            "vertex-openai": {
+              name: "Vertex OpenAI",
+              npm: "@ai-sdk/google-vertex",
+              env: ["GOOGLE_APPLICATION_CREDENTIALS"],
+              models: {
+                "gpt-4": {
+                  name: "GPT-4",
+                  provider: {
+                    npm: "@ai-sdk/openai-compatible",
+                    api: "https://api.openai.com/v1",
+                  },
+                },
+              },
+              options: {
+                project: "test-project",
+                location: "us-central1",
+              },
+            },
+          },
+        }),
+      )
+    },
+  })
+
+  await Instance.provide({
+    directory: tmp.path,
+    init: async () => {
+      Env.set("GOOGLE_APPLICATION_CREDENTIALS", "test-creds")
+    },
+    fn: async () => {
+      const providers = await Provider.list()
+      const model = providers["vertex-openai"].models["gpt-4"]
+
+      expect(model).toBeDefined()
+      expect(model.api.npm).toBe("@ai-sdk/openai-compatible")
+    },
+  })
+})
+