fix(provider): add Merge Gateway reasoning variants (#41867)

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

@@ -3370,6 +3370,7 @@ describe("ProviderTransform.reasoningVariants", () => {
     ["@ai-sdk/togetherai", { reasoningEffort: "high" }],
     ["venice-ai-sdk-provider", { reasoningEffort: "high" }],
     ["ai-gateway-provider", { reasoningEffort: "high" }],
+    ["merge-gateway-ai-sdk-provider", { reasoningEffort: "high" }],
     ["@ai-sdk/amazon-bedrock", { reasoningConfig: { type: "enabled", maxReasoningEffort: "high" } }],
   ])("converts effort for %s", (npm, expected, ...args) => {
     const id = args[0] as string | undefined
@@ -5555,6 +5556,25 @@ describe("ProviderTransform.providerOptions - ai-gateway-provider", () => {
   })
 })
 
+describe("ProviderTransform.providerOptions - merge-gateway-ai-sdk-provider", () => {
+  const model = {
+    id: "merge-gateway/openai/gpt-5.6-sol",
+    providerID: "merge-gateway",
+    api: {
+      id: "openai/gpt-5.6-sol",
+      url: "https://api-gateway.merge.dev/v1/ai-sdk",
+      npm: "merge-gateway-ai-sdk-provider",
+    },
+    capabilities: { reasoning: true },
+  } as any
+
+  test("routes normalized effort under the adapter's mergeGateway key", () => {
+    expect(ProviderTransform.providerOptions(model, { reasoningEffort: "high" })).toEqual({
+      mergeGateway: { reasoningEffort: "high" },
+    })
+  })
+})
+
 describe("ProviderTransform.options - kimi family adaptive thinking", () => {
   const createModel = (overrides: Record<string, any> = {}) =>
     ({