fix: exclude gpt-oss from codex bucket in model-services discovery

gpt-oss-* contains 'gpt-' so it matched the codex bucket, but it's a
chat-completions-only OSS model (served via /ai-gateway/mlflow/v1), not an
openai-responses model. Broadening _OSS_MODEL_FAMILIES to include gpt-oss put
it in BOTH codex_models and oss_models, so it was offered under Pi's
databricks-openai provider too — where the openai-responses route 400s for it.
Exclude gpt-oss from the codex bucket so it's OSS-only.

Author: dgokeeffe

src/ucode/databricks.py

@@ -1337,7 +1337,10 @@ def discover_model_services(
         if candidates:
             claude_models[family] = candidates[0]
 
-    codex_models = [m for m in ids if "gpt-" in m]
+    # `gpt-oss-*` also contains "gpt-" but is a chat-completions-only OSS model
+    # (served via /ai-gateway/mlflow/v1), NOT an openai-responses codex model —
+    # exclude it here so it isn't offered under the codex provider (which 400s).
+    codex_models = [m for m in ids if "gpt-" in m and "gpt-oss" not in m]
     gemini_models = sorted([m for m in ids if "gemini-" in m], key=model_version_sort_key)
 
     oss_models = [m for m in ids if _is_oss_chat_model(m)]

tests/test_databricks.py

@@ -286,6 +286,26 @@ def test_embedding_model_sharing_family_substring_excluded(self, monkeypatch):
         assert "system.ai.qwen35-122b-a10b" in oss
         assert "system.ai.qwen3-embedding-0-6b" not in oss
 
+    def test_gpt_oss_is_oss_not_codex(self, monkeypatch):
+        # gpt-oss-* contains "gpt-" but is chat-completions-only, not an
+        # openai-responses codex model. It must bucket into oss ONLY, never
+        # codex (whose openai-responses route would 400 for it).
+        payload = {
+            "model_services": [
+                _model_service("system.ai.gpt-5"),
+                _model_service("system.ai.gpt-oss-120b"),
+            ]
+        }
+        monkeypatch.setattr(
+            db_mod, "_http_get_json", lambda url, token, timeout=10: (payload, None)
+        )
+
+        _, codex, _, oss, _ = db_mod.discover_model_services(WS, "token")
+
+        assert codex == ["system.ai.gpt-5"]
+        assert "system.ai.gpt-oss-120b" in oss
+        assert "system.ai.gpt-oss-120b" not in codex
+
     def test_paginates_via_next_page_token(self, monkeypatch):
         pages = {
             None: {