diff --git a/internal/translator/openai/openai/responses/openai_openai-responses_response.go b/internal/translator/openai/openai/responses/openai_openai-responses_response.go
index 6f9e2a5e..fcaaa638 100644
--- a/internal/translator/openai/openai/responses/openai_openai-responses_response.go
+++ b/internal/translator/openai/openai/responses/openai_openai-responses_response.go
@@ -479,7 +479,13 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 						existingCallID := st.FuncCallIDs[key]
 						effectiveCallID := existingCallID
 						shouldEmitItem := false
-						if existingCallID == "" && newCallID != "" {
+						if existingCallID == "" {
+							if newCallID == "" {
+								// Some OpenAI-compatible providers omit tool_call ids in
+								// streaming deltas; synthesize one so the Responses event
+								// chain (output_item.added/done) still fires for Codex.
+								newCallID = fmt.Sprintf("call_%s_%d_%d", st.ResponseID, idx, toolIndex)
+							}
 							effectiveCallID = newCallID
 							st.FuncCallIDs[key] = newCallID
 							st.FuncOutputIx[key] = allocOutputIndex()
@@ -758,8 +764,13 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponsesNonStream(_ context.Co
 
 				// Function/tool calls
 				if tcs := msg.Get("tool_calls"); tcs.Exists() && tcs.IsArray() {
-					tcs.ForEach(func(_, tc gjson.Result) bool {
+					tcs.ForEach(func(tcIndex, tc gjson.Result) bool {
 						callID := tc.Get("id").String()
+						if callID == "" {
+							// Providers may omit tool_call ids; synthesize one so the
+							// function_call item stays usable for Codex round-trips.
+							callID = fmt.Sprintf("call_%s_%d_%d", id, choice.Get("index").Int(), tcIndex.Int())
+						}
 						name := tc.Get("function.name").String()
 						args := tc.Get("function.arguments").String()
 						item := []byte(`{"id":"","type":"function_call","status":"completed","arguments":"","call_id":"","name":""}`)