src/ix/genai/ollama_client.py

@@ -159,21 +159,7 @@ class OllamaClient:
         request_kwargs: dict[str, Any],
         response_schema: type[BaseModel],
     ) -> dict[str, Any]:
-        """Map provider-neutral kwargs to Ollama's /api/chat body.
+        """Map provider-neutral kwargs to Ollama's /api/chat body."""
-
-        Schema strategy for Ollama 0.11.8: we pass ``format="json"`` (loose
-        JSON mode) rather than the full Pydantic schema. The llama.cpp
-        structured-output implementation in 0.11.8 segfaults on schemas
-        involving ``anyOf``, ``$ref``, or ``pattern`` — which Pydantic v2
-        emits for Optional / nested-model / Decimal fields.
-
-        In loose JSON mode Ollama guarantees only syntactically-valid
-        JSON; we enforce the schema on our side by catching the Pydantic
-        ``ValidationError`` at parse time and raising IX_002_001. The
-        system prompt (built upstream in GenAIStep) already tells the
-        model what JSON shape to emit, so loose mode is the right
-        abstraction layer here.
-        """
 
         messages = self._translate_messages(
             list(request_kwargs.get("messages") or [])
@@ -182,7 +168,9 @@ class OllamaClient:
             "model": request_kwargs.get("model"),
             "messages": messages,
             "stream": False,
-            "format": "json",
+            "format": _sanitise_schema_for_ollama(
+                response_schema.model_json_schema()
+            ),
         }
 
         options: dict[str, Any] = {}

tests/unit/test_ollama_client.py

@@ -79,10 +79,13 @@ class TestInvokeHappyPath:
         body_json = json.loads(body)
         assert body_json["model"] == "gpt-oss:20b"
         assert body_json["stream"] is False
-        # format is "json" (loose mode): Ollama 0.11.8 segfaults on full
+        # Format is the pydantic schema with Optional `anyOf [T, null]`
-        # Pydantic schemas. We pass the schema via the system prompt
+        # patterns collapsed to just T — Ollama 0.11.8 segfaults on the
-        # upstream and validate on parse.
+        # anyOf+null shape, so we sanitise before sending.
-        assert body_json["format"] == "json"
+        fmt = body_json["format"]
+        assert fmt["properties"]["bank_name"] == {"title": "Bank Name", "type": "string"}
+        assert fmt["properties"]["account_number"]["type"] == "string"
+        assert "anyOf" not in fmt["properties"]["account_number"]
         assert body_json["options"]["temperature"] == 0.2
         assert "reasoning_effort" not in body_json
         assert body_json["messages"] == [