fix(xai): resolve Grok Build context for OAuth

tests/agent/test_model_metadata.py

@@ -164,6 +164,7 @@ class TestDefaultContextLengths:
             "grok-4-1-fast": 2000000,
             "grok-4-fast": 2000000,
             "grok-4": 256000,
+            "grok-build": 256000,
             "grok-code-fast": 256000,
             "grok-3": 131072,
             "grok-2": 131072,
@@ -195,6 +196,7 @@ class TestDefaultContextLengths:
                 ("grok-4-fast-non-reasoning", 2000000),
                 ("grok-4", 256000),
                 ("grok-4-0709", 256000),
+                ("grok-build-0.1", 256000),
                 ("grok-code-fast-1", 256000),
                 ("grok-3", 131072),
                 ("grok-3-mini", 131072),
@@ -210,6 +212,32 @@ class TestDefaultContextLengths:
                     f"{model_id}: expected {expected_ctx}, got {actual}"
                 )
 
+    def test_xai_oauth_grok_build_uses_xai_models_dev_context(self):
+        """xAI OAuth should share the xAI provider metadata path.
+
+        The xAI /v1/models endpoint does not currently include context fields
+        for grok-build-0.1, so this guards against falling through to the
+        generic "grok" 131k fallback when using OAuth credentials.
+        """
+        registry = {
+            "xai": {
+                "models": {
+                    "grok-build-0.1": {
+                        "limit": {"context": 256000, "output": 64000},
+                    },
+                },
+            },
+        }
+        with patch("agent.model_metadata.get_cached_context_length", return_value=None), \
+             patch("agent.model_metadata._query_ollama_api_show", return_value=None), \
+             patch("agent.models_dev.fetch_models_dev", return_value=registry):
+            assert get_model_context_length(
+                "grok-build-0.1",
+                provider="xai-oauth",
+                base_url="https://api.x.ai/v1",
+                api_key="oauth-token",
+            ) == 256000
+
     def test_deepseek_v4_models_1m_context(self):
         from agent.model_metadata import get_model_context_length
         from unittest.mock import patch as mock_patch