fix: preserve assistant text when tool calls present in Responses API conversion

When converting assistant messages with both text and tool calls to the
Responses API format, the text content was silently discarded via continue.
Emit the text as a separate assistant message before the function calls.

Includes a regression test.

Assisted-By: docker-agent

Author: dgageot

pkg/model/provider/openai/client.go

@@ -565,20 +565,30 @@ func convertMessagesToResponseInput(messages []chat.Message) []responses.Respons
 					},
 				}
 			} else {
-				// Assistant message with tool calls - convert to response input item with function calls
+				// Assistant message with tool calls - emit text as a separate assistant
+				// message before the function calls so it is not lost.
+				if strings.TrimSpace(msg.Content) != "" {
+					input = append(input, responses.ResponseInputItemUnionParam{
+						OfMessage: &responses.EasyInputMessageParam{
+							Role: responses.EasyInputMessageRoleAssistant,
+							Content: responses.EasyInputMessageContentUnionParam{
+								OfString: param.NewOpt(msg.Content),
+							},
+						},
+					})
+				}
 				for _, toolCall := range msg.ToolCalls {
 					if toolCall.Type == "function" {
-						funcCallItem := responses.ResponseInputItemUnionParam{
+						input = append(input, responses.ResponseInputItemUnionParam{
 							OfFunctionCall: &responses.ResponseFunctionToolCallParam{
 								CallID:    toolCall.ID,
 								Name:      toolCall.Function.Name,
 								Arguments: toolCall.Function.Arguments,
 							},
-						}
-						input = append(input, funcCallItem)
+						})
 					}
 				}
-				continue // Don't add the assistant message itself
+				continue
 			}
 
 		case chat.MessageRoleSystem:

pkg/model/provider/openai/client_test.go

@@ -46,6 +46,41 @@ func TestConvertMessagesToResponseInput_OrphanedFunctionCall(t *testing.T) {
 	assert.Contains(t, outputIDs, "call_2")
 }
 
+func TestConvertMessagesToResponseInput_AssistantTextWithToolCalls(t *testing.T) {
+	// When an assistant message has both text content and tool calls,
+	// the text must not be silently discarded.
+	messages := []chat.Message{
+		{Role: chat.MessageRoleUser, Content: "hello"},
+		{
+			Role:    chat.MessageRoleAssistant,
+			Content: "Let me search that for you.",
+			ToolCalls: []tools.ToolCall{
+				{ID: "call_1", Type: "function", Function: tools.FunctionCall{Name: "search", Arguments: `{"q":"test"}`}},
+			},
+		},
+		{Role: chat.MessageRoleTool, Content: "result", ToolCallID: "call_1"},
+	}
+
+	input := convertMessagesToResponseInput(messages)
+
+	// We expect: user message, assistant text message, function call, function call output.
+	var foundAssistantText bool
+	var foundFunctionCall bool
+	for _, item := range input {
+		if item.OfMessage != nil && item.OfMessage.Role == "assistant" {
+			if item.OfMessage.Content.OfString.Valid() && item.OfMessage.Content.OfString.Value == "Let me search that for you." {
+				foundAssistantText = true
+			}
+		}
+		if item.OfFunctionCall != nil && item.OfFunctionCall.CallID == "call_1" {
+			foundFunctionCall = true
+		}
+	}
+
+	assert.True(t, foundFunctionCall, "function call should be present")
+	assert.True(t, foundAssistantText, "assistant text content should not be discarded when tool calls are present")
+}
+
 func TestConvertMessagesToResponseInput_NoOrphans(t *testing.T) {
 	// All tool calls have matching results — no placeholder needed.
 	messages := []chat.Message{