fix(core): route Vertex Gemini through native provider (#43433)

Signed-off-by: Major Hayden <major@mhtx.net>

packages/core/src/aisdk-native.ts

@@ -51,6 +51,19 @@ export function map(input: MapInput): Mapping | undefined {
           ...mapGoogleOptions(input.settings),
         },
       }
+    case "@ai-sdk/google-vertex":
+      return {
+        package: "@opencode-ai/ai/providers/google-vertex",
+        settings: {
+          ...baseSettings,
+          ...(typeof input.settings.accessToken === "string" ? { accessToken: input.settings.accessToken } : {}),
+          ...mapAPIKey(input.settings),
+          ...(typeof input.settings.location === "string" ? { location: input.settings.location } : {}),
+          ...(typeof input.settings.project === "string" ? { project: input.settings.project } : {}),
+          ...mapGoogleOptions(input.settings),
+        },
+        ...(isStringRecord(input.settings.headers) ? { headers: input.settings.headers } : {}),
+      }
     case "@ai-sdk/google-vertex/anthropic":
       return {
         package: "@opencode-ai/ai/providers/google-vertex/messages",

packages/core/test/aisdk-native.test.ts

@@ -273,6 +273,29 @@ describe("AISDKNative", () => {
     })
   })
 
+  test("maps Vertex Gemini settings to the native Gemini route", () => {
+    expect(
+      map("@ai-sdk/google-vertex", {
+        accessToken: "vertex-token",
+        baseURL: "https://vertex.example/v1",
+        headers: { "x-test": "value" },
+        location: "eu",
+        project: "vertex-project",
+        thinkingConfig: { thinkingLevel: "high" },
+      }),
+    ).toEqual({
+      package: "@opencode-ai/ai/providers/google-vertex",
+      settings: {
+        accessToken: "vertex-token",
+        baseURL: "https://vertex.example/v1",
+        location: "eu",
+        project: "vertex-project",
+        providerOptions: { gemini: { thinkingConfig: { thinkingLevel: "high" } } },
+      },
+      headers: { "x-test": "value" },
+    })
+  })
+
   test("maps Vertex Anthropic settings to native Messages", () => {
     expect(
       map("@ai-sdk/google-vertex/anthropic", {