feat(ai): add xAI device OAuth and route grok-4.5 through Responses (#6651)

* feat(ai): add xAI device OAuth and route grok-4.5 through Responses

Add xAI device-code OAuth alongside XAI_API_KEY. Route only grok-4.5
through Responses with low/medium/high reasoning; other xAI models stay
on Completions.

* fix(ai): tolerate xAI device-code interval 0 and correct token poll error label

---------

Co-authored-by: Jaaneek <Jaaneek@users.noreply.github.com>

packages/ai/scripts/generate-models.ts

@@ -255,6 +255,14 @@ const OPENAI_RESPONSES_NONE_REASONING_MODELS = new Set([
 	"gpt-5.6-terra",
 	"gpt-5.6-luna",
 ]);
+const XAI_RESPONSES_MODEL_ID = "grok-4.5";
+const XAI_RESPONSES_EFFORT_LEVEL_MAP = {
+	off: null,
+	minimal: null,
+} as const;
+const XAI_RESPONSES_COMPAT: OpenAIResponsesCompat = {
+	supportsLongCacheRetention: false,
+};
 
 const OPENCODE_OPENAI_COMPLETIONS_LONG_CACHE_RETENTION_UNSUPPORTED_MODELS = new Set([
 	"opencode:deepseek-v4-flash",
@@ -538,6 +546,9 @@ function applyThinkingLevelMetadata(model: Model<any>): void {
 	) {
 		mergeThinkingLevelMap(model, { off: "none" });
 	}
+	if (model.provider === "xai" && model.api === "openai-responses" && model.id === XAI_RESPONSES_MODEL_ID) {
+		mergeThinkingLevelMap(model, XAI_RESPONSES_EFFORT_LEVEL_MAP);
+	}
 	if (supportsOpenAiXhigh(model.id)) {
 		mergeThinkingLevelMap(model, { xhigh: "xhigh" });
 	}
@@ -1126,13 +1137,15 @@ async function loadModelsDevData(): Promise<Model<any>[]> {
 			for (const [modelId, model] of Object.entries(data.xai.models)) {
 				const m = model as ModelsDevModel;
 				if (m.tool_call !== true) continue;
+				const useResponsesApi = modelId === XAI_RESPONSES_MODEL_ID;
 
 				models.push({
 					id: modelId,
 					name: m.name || modelId,
-					api: "openai-completions",
+					api: useResponsesApi ? "openai-responses" : "openai-completions",
 					provider: "xai",
 					baseUrl: "https://api.x.ai/v1",
+					...(useResponsesApi ? { compat: { ...XAI_RESPONSES_COMPAT } } : {}),
 					reasoning: m.reasoning === true,
 					input: m.modalities?.input?.includes("image") ? ["text", "image"] : ["text"],
 					cost: {