openai: always provide reasoning

We were missing passing along thinking if content was nil (as opposed
to empty string)

Also added a test for content not being passed, which was the real cause
of <https://github.com/ollama/ollama/issues/11704>, since with the way
`Content` is typed, not passing it and empty string are distinct

openai/openai.go

@@ -478,6 +478,7 @@ func fromChatRequest(r ChatCompletionRequest) (*api.ChatRequest, error) {
 				if toolName != "" {
 					messages[len(messages)-1].ToolName = toolName
 				}
+				messages[len(messages)-1].Thinking = msg.Reasoning
 			}
 		default:
 			// content is only optional if tool calls are present
@@ -493,7 +494,7 @@ func fromChatRequest(r ChatCompletionRequest) (*api.ChatRequest, error) {
 					return nil, errors.New("invalid tool call arguments")
 				}
 			}
-			messages = append(messages, api.Message{Role: msg.Role, ToolCalls: toolCalls})
+			messages = append(messages, api.Message{Role: msg.Role, Thinking: msg.Reasoning, ToolCalls: toolCalls})
 		}
 	}
 

openai/openai_test.go

@@ -274,6 +274,83 @@ func TestChatMiddleware(t *testing.T) {
 				Stream: &False,
 			},
 		},
+		{
+			name: "chat handler with tools and empty content",
+			body: `{
+				"model": "test-model",
+				"messages": [
+					{"role": "user", "content": "What's the weather like in Paris Today?"},
+					{"role": "assistant", "content": "", "tool_calls": [{"id": "id", "type": "function", "function": {"name": "get_current_weather", "arguments": "{\"location\": \"Paris, France\", \"format\": \"celsius\"}"}}]}
+				]
+			}`,
+			req: api.ChatRequest{
+				Model: "test-model",
+				Messages: []api.Message{
+					{
+						Role:    "user",
+						Content: "What's the weather like in Paris Today?",
+					},
+					{
+						Role: "assistant",
+						ToolCalls: []api.ToolCall{
+							{
+								Function: api.ToolCallFunction{
+									Name: "get_current_weather",
+									Arguments: map[string]any{
+										"location": "Paris, France",
+										"format":   "celsius",
+									},
+								},
+							},
+						},
+					},
+				},
+				Options: map[string]any{
+					"temperature": 1.0,
+					"top_p":       1.0,
+				},
+				Stream: &False,
+			},
+		},
+		{
+			name: "chat handler with tools and thinking content",
+			body: `{
+				"model": "test-model",
+				"messages": [
+					{"role": "user", "content": "What's the weather like in Paris Today?"},
+					{"role": "assistant", "reasoning": "Let's see what the weather is like in Paris", "tool_calls": [{"id": "id", "type": "function", "function": {"name": "get_current_weather", "arguments": "{\"location\": \"Paris, France\", \"format\": \"celsius\"}"}}]}
+				]
+			}`,
+			req: api.ChatRequest{
+				Model: "test-model",
+				Messages: []api.Message{
+					{
+						Role:    "user",
+						Content: "What's the weather like in Paris Today?",
+					},
+					{
+						Role:     "assistant",
+						Thinking: "Let's see what the weather is like in Paris",
+						ToolCalls: []api.ToolCall{
+							{
+								Function: api.ToolCallFunction{
+									Name: "get_current_weather",
+									Arguments: map[string]any{
+										"location": "Paris, France",
+										"format":   "celsius",
+									},
+								},
+							},
+						},
+					},
+				},
+				Options: map[string]any{
+					"temperature": 1.0,
+					"top_p":       1.0,
+				},
+				Stream: &False,
+			},
+		},
 		{
 			name: "tool response with call ID",
 			body: `{