Merge pull request #2231 from 7RPH/fix/responses-stream-multi-tool-calls

fix: preserve separate streamed tool calls in Responses API

internal/translator/openai/openai/responses/openai_openai-responses_response.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"sort"
 	"strings"
 	"sync/atomic"
 	"time"
@@ -16,6 +17,7 @@ import (
 type oaiToResponsesStateReasoning struct {
 	ReasoningID   string
 	ReasoningData string
+	OutputIndex   int
 }
 type oaiToResponsesState struct {
 	Seq            int
@@ -29,16 +31,19 @@ type oaiToResponsesState struct {
 	MsgTextBuf   map[int]*strings.Builder
 	ReasoningBuf strings.Builder
 	Reasonings   []oaiToResponsesStateReasoning
-	FuncArgsBuf  map[int]*strings.Builder // index -> args
+	FuncArgsBuf  map[string]*strings.Builder
-	FuncNames    map[int]string           // index -> name
+	FuncNames    map[string]string
-	FuncCallIDs  map[int]string           // index -> call_id
+	FuncCallIDs  map[string]string
+	FuncOutputIx map[string]int
+	MsgOutputIx  map[int]int
+	NextOutputIx int
 	// message item state per output index
 	MsgItemAdded    map[int]bool // whether response.output_item.added emitted for message
 	MsgContentAdded map[int]bool // whether response.content_part.added emitted for message
 	MsgItemDone     map[int]bool // whether message done events were emitted
 	// function item done state
-	FuncArgsDone map[int]bool
+	FuncArgsDone map[string]bool
-	FuncItemDone map[int]bool
+	FuncItemDone map[string]bool
 	// usage aggregation
 	PromptTokens     int64
 	CachedTokens     int64
@@ -60,15 +65,17 @@ func emitRespEvent(event string, payload []byte) []byte {
 func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context, modelName string, originalRequestRawJSON, requestRawJSON, rawJSON []byte, param *any) [][]byte {
 	if *param == nil {
 		*param = &oaiToResponsesState{
-			FuncArgsBuf:     make(map[int]*strings.Builder),
+			FuncArgsBuf:     make(map[string]*strings.Builder),
-			FuncNames:       make(map[int]string),
+			FuncNames:       make(map[string]string),
-			FuncCallIDs:     make(map[int]string),
+			FuncCallIDs:     make(map[string]string),
+			FuncOutputIx:    make(map[string]int),
+			MsgOutputIx:     make(map[int]int),
 			MsgTextBuf:      make(map[int]*strings.Builder),
 			MsgItemAdded:    make(map[int]bool),
 			MsgContentAdded: make(map[int]bool),
 			MsgItemDone:     make(map[int]bool),
-			FuncArgsDone:    make(map[int]bool),
+			FuncArgsDone:    make(map[string]bool),
-			FuncItemDone:    make(map[int]bool),
+			FuncItemDone:    make(map[string]bool),
 			Reasonings:      make([]oaiToResponsesStateReasoning, 0),
 		}
 	}
@@ -125,6 +132,12 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 	}
 
 	nextSeq := func() int { st.Seq++; return st.Seq }
+	allocOutputIndex := func() int {
+		ix := st.NextOutputIx
+		st.NextOutputIx++
+		return ix
+	}
+	toolStateKey := func(outputIndex, toolIndex int) string { return fmt.Sprintf("%d:%d", outputIndex, toolIndex) }
 	var out [][]byte
 
 	if !st.Started {
@@ -135,14 +148,17 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 		st.ReasoningBuf.Reset()
 		st.ReasoningID = ""
 		st.ReasoningIndex = 0
-		st.FuncArgsBuf = make(map[int]*strings.Builder)
+		st.FuncArgsBuf = make(map[string]*strings.Builder)
-		st.FuncNames = make(map[int]string)
+		st.FuncNames = make(map[string]string)
-		st.FuncCallIDs = make(map[int]string)
+		st.FuncCallIDs = make(map[string]string)
+		st.FuncOutputIx = make(map[string]int)
+		st.MsgOutputIx = make(map[int]int)
+		st.NextOutputIx = 0
 		st.MsgItemAdded = make(map[int]bool)
 		st.MsgContentAdded = make(map[int]bool)
 		st.MsgItemDone = make(map[int]bool)
-		st.FuncArgsDone = make(map[int]bool)
+		st.FuncArgsDone = make(map[string]bool)
-		st.FuncItemDone = make(map[int]bool)
+		st.FuncItemDone = make(map[string]bool)
 		st.PromptTokens = 0
 		st.CachedTokens = 0
 		st.CompletionTokens = 0
@@ -185,7 +201,7 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 		outputItemDone, _ = sjson.SetBytes(outputItemDone, "item.summary.text", text)
 		out = append(out, emitRespEvent("response.output_item.done", outputItemDone))
 
-		st.Reasonings = append(st.Reasonings, oaiToResponsesStateReasoning{ReasoningID: st.ReasoningID, ReasoningData: text})
+		st.Reasonings = append(st.Reasonings, oaiToResponsesStateReasoning{ReasoningID: st.ReasoningID, ReasoningData: text, OutputIndex: st.ReasoningIndex})
 		st.ReasoningID = ""
 	}
 
@@ -201,10 +217,14 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 						stopReasoning(st.ReasoningBuf.String())
 						st.ReasoningBuf.Reset()
 					}
+					if _, exists := st.MsgOutputIx[idx]; !exists {
+						st.MsgOutputIx[idx] = allocOutputIndex()
+					}
+					msgOutputIndex := st.MsgOutputIx[idx]
 					if !st.MsgItemAdded[idx] {
 						item := []byte(`{"type":"response.output_item.added","sequence_number":0,"output_index":0,"item":{"id":"","type":"message","status":"in_progress","content":[],"role":"assistant"}}`)
 						item, _ = sjson.SetBytes(item, "sequence_number", nextSeq())
-						item, _ = sjson.SetBytes(item, "output_index", idx)
+						item, _ = sjson.SetBytes(item, "output_index", msgOutputIndex)
 						item, _ = sjson.SetBytes(item, "item.id", fmt.Sprintf("msg_%s_%d", st.ResponseID, idx))
 						out = append(out, emitRespEvent("response.output_item.added", item))
 						st.MsgItemAdded[idx] = true
@@ -213,7 +233,7 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 						part := []byte(`{"type":"response.content_part.added","sequence_number":0,"item_id":"","output_index":0,"content_index":0,"part":{"type":"output_text","annotations":[],"logprobs":[],"text":""}}`)
 						part, _ = sjson.SetBytes(part, "sequence_number", nextSeq())
 						part, _ = sjson.SetBytes(part, "item_id", fmt.Sprintf("msg_%s_%d", st.ResponseID, idx))
-						part, _ = sjson.SetBytes(part, "output_index", idx)
+						part, _ = sjson.SetBytes(part, "output_index", msgOutputIndex)
 						part, _ = sjson.SetBytes(part, "content_index", 0)
 						out = append(out, emitRespEvent("response.content_part.added", part))
 						st.MsgContentAdded[idx] = true
@@ -222,7 +242,7 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 					msg := []byte(`{"type":"response.output_text.delta","sequence_number":0,"item_id":"","output_index":0,"content_index":0,"delta":"","logprobs":[]}`)
 					msg, _ = sjson.SetBytes(msg, "sequence_number", nextSeq())
 					msg, _ = sjson.SetBytes(msg, "item_id", fmt.Sprintf("msg_%s_%d", st.ResponseID, idx))
-					msg, _ = sjson.SetBytes(msg, "output_index", idx)
+					msg, _ = sjson.SetBytes(msg, "output_index", msgOutputIndex)
 					msg, _ = sjson.SetBytes(msg, "content_index", 0)
 					msg, _ = sjson.SetBytes(msg, "delta", c.String())
 					out = append(out, emitRespEvent("response.output_text.delta", msg))
@@ -238,10 +258,10 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 					// On first appearance, add reasoning item and part
 					if st.ReasoningID == "" {
 						st.ReasoningID = fmt.Sprintf("rs_%s_%d", st.ResponseID, idx)
-						st.ReasoningIndex = idx
+						st.ReasoningIndex = allocOutputIndex()
 						item := []byte(`{"type":"response.output_item.added","sequence_number":0,"output_index":0,"item":{"id":"","type":"reasoning","status":"in_progress","summary":[]}}`)
 						item, _ = sjson.SetBytes(item, "sequence_number", nextSeq())
-						item, _ = sjson.SetBytes(item, "output_index", idx)
+						item, _ = sjson.SetBytes(item, "output_index", st.ReasoningIndex)
 						item, _ = sjson.SetBytes(item, "item.id", st.ReasoningID)
 						out = append(out, emitRespEvent("response.output_item.added", item))
 						part := []byte(`{"type":"response.reasoning_summary_part.added","sequence_number":0,"item_id":"","output_index":0,"summary_index":0,"part":{"type":"summary_text","text":""}}`)
@@ -269,6 +289,7 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 					// Before emitting any function events, if a message is open for this index,
 					// close its text/content to match Codex expected ordering.
 					if st.MsgItemAdded[idx] && !st.MsgItemDone[idx] {
+						msgOutputIndex := st.MsgOutputIx[idx]
 						fullText := ""
 						if b := st.MsgTextBuf[idx]; b != nil {
 							fullText = b.String()
@@ -276,7 +297,7 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 						done := []byte(`{"type":"response.output_text.done","sequence_number":0,"item_id":"","output_index":0,"content_index":0,"text":"","logprobs":[]}`)
 						done, _ = sjson.SetBytes(done, "sequence_number", nextSeq())
 						done, _ = sjson.SetBytes(done, "item_id", fmt.Sprintf("msg_%s_%d", st.ResponseID, idx))
-						done, _ = sjson.SetBytes(done, "output_index", idx)
+						done, _ = sjson.SetBytes(done, "output_index", msgOutputIndex)
 						done, _ = sjson.SetBytes(done, "content_index", 0)
 						done, _ = sjson.SetBytes(done, "text", fullText)
 						out = append(out, emitRespEvent("response.output_text.done", done))
@@ -284,69 +305,72 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 						partDone := []byte(`{"type":"response.content_part.done","sequence_number":0,"item_id":"","output_index":0,"content_index":0,"part":{"type":"output_text","annotations":[],"logprobs":[],"text":""}}`)
 						partDone, _ = sjson.SetBytes(partDone, "sequence_number", nextSeq())
 						partDone, _ = sjson.SetBytes(partDone, "item_id", fmt.Sprintf("msg_%s_%d", st.ResponseID, idx))
-						partDone, _ = sjson.SetBytes(partDone, "output_index", idx)
+						partDone, _ = sjson.SetBytes(partDone, "output_index", msgOutputIndex)
 						partDone, _ = sjson.SetBytes(partDone, "content_index", 0)
 						partDone, _ = sjson.SetBytes(partDone, "part.text", fullText)
 						out = append(out, emitRespEvent("response.content_part.done", partDone))
 
 						itemDone := []byte(`{"type":"response.output_item.done","sequence_number":0,"output_index":0,"item":{"id":"","type":"message","status":"completed","content":[{"type":"output_text","annotations":[],"logprobs":[],"text":""}],"role":"assistant"}}`)
 						itemDone, _ = sjson.SetBytes(itemDone, "sequence_number", nextSeq())
-						itemDone, _ = sjson.SetBytes(itemDone, "output_index", idx)
+						itemDone, _ = sjson.SetBytes(itemDone, "output_index", msgOutputIndex)
 						itemDone, _ = sjson.SetBytes(itemDone, "item.id", fmt.Sprintf("msg_%s_%d", st.ResponseID, idx))
 						itemDone, _ = sjson.SetBytes(itemDone, "item.content.0.text", fullText)
 						out = append(out, emitRespEvent("response.output_item.done", itemDone))
 						st.MsgItemDone[idx] = true
 					}
 
-					// Only emit item.added once per tool call and preserve call_id across chunks.
+					tcs.ForEach(func(_, tc gjson.Result) bool {
-					newCallID := tcs.Get("0.id").String()
+						toolIndex := int(tc.Get("index").Int())
-					nameChunk := tcs.Get("0.function.name").String()
+						key := toolStateKey(idx, toolIndex)
-					if nameChunk != "" {
+						newCallID := tc.Get("id").String()
-						st.FuncNames[idx] = nameChunk
+						nameChunk := tc.Get("function.name").String()
-					}
+						if nameChunk != "" {
-					existingCallID := st.FuncCallIDs[idx]
+							st.FuncNames[key] = nameChunk
-					effectiveCallID := existingCallID
-					shouldEmitItem := false
-					if existingCallID == "" && newCallID != "" {
-						// First time seeing a valid call_id for this index
-						effectiveCallID = newCallID
-						st.FuncCallIDs[idx] = newCallID
-						shouldEmitItem = true
-					}
-
-					if shouldEmitItem && effectiveCallID != "" {
-						o := []byte(`{"type":"response.output_item.added","sequence_number":0,"output_index":0,"item":{"id":"","type":"function_call","status":"in_progress","arguments":"","call_id":"","name":""}}`)
-						o, _ = sjson.SetBytes(o, "sequence_number", nextSeq())
-						o, _ = sjson.SetBytes(o, "output_index", idx)
-						o, _ = sjson.SetBytes(o, "item.id", fmt.Sprintf("fc_%s", effectiveCallID))
-						o, _ = sjson.SetBytes(o, "item.call_id", effectiveCallID)
-						name := st.FuncNames[idx]
-						o, _ = sjson.SetBytes(o, "item.name", name)
-						out = append(out, emitRespEvent("response.output_item.added", o))
-					}
-
-					// Ensure args buffer exists for this index
-					if st.FuncArgsBuf[idx] == nil {
-						st.FuncArgsBuf[idx] = &strings.Builder{}
-					}
-
-					// Append arguments delta if available and we have a valid call_id to reference
-					if args := tcs.Get("0.function.arguments"); args.Exists() && args.String() != "" {
-						// Prefer an already known call_id; fall back to newCallID if first time
-						refCallID := st.FuncCallIDs[idx]
-						if refCallID == "" {
-							refCallID = newCallID
 						}
-						if refCallID != "" {
+
-							ad := []byte(`{"type":"response.function_call_arguments.delta","sequence_number":0,"item_id":"","output_index":0,"delta":""}`)
+						existingCallID := st.FuncCallIDs[key]
-							ad, _ = sjson.SetBytes(ad, "sequence_number", nextSeq())
+						effectiveCallID := existingCallID
-							ad, _ = sjson.SetBytes(ad, "item_id", fmt.Sprintf("fc_%s", refCallID))
+						shouldEmitItem := false
-							ad, _ = sjson.SetBytes(ad, "output_index", idx)
+						if existingCallID == "" && newCallID != "" {
-							ad, _ = sjson.SetBytes(ad, "delta", args.String())
+							effectiveCallID = newCallID
-							out = append(out, emitRespEvent("response.function_call_arguments.delta", ad))
+							st.FuncCallIDs[key] = newCallID
+							st.FuncOutputIx[key] = allocOutputIndex()
+							shouldEmitItem = true
 						}
-						st.FuncArgsBuf[idx].WriteString(args.String())
+
-					}
+						if shouldEmitItem && effectiveCallID != "" {
+							outputIndex := st.FuncOutputIx[key]
+							o := []byte(`{"type":"response.output_item.added","sequence_number":0,"output_index":0,"item":{"id":"","type":"function_call","status":"in_progress","arguments":"","call_id":"","name":""}}`)
+							o, _ = sjson.SetBytes(o, "sequence_number", nextSeq())
+							o, _ = sjson.SetBytes(o, "output_index", outputIndex)
+							o, _ = sjson.SetBytes(o, "item.id", fmt.Sprintf("fc_%s", effectiveCallID))
+							o, _ = sjson.SetBytes(o, "item.call_id", effectiveCallID)
+							o, _ = sjson.SetBytes(o, "item.name", st.FuncNames[key])
+							out = append(out, emitRespEvent("response.output_item.added", o))
+						}
+
+						if st.FuncArgsBuf[key] == nil {
+							st.FuncArgsBuf[key] = &strings.Builder{}
+						}
+
+						if args := tc.Get("function.arguments"); args.Exists() && args.String() != "" {
+							refCallID := st.FuncCallIDs[key]
+							if refCallID == "" {
+								refCallID = newCallID
+							}
+							if refCallID != "" {
+								outputIndex := st.FuncOutputIx[key]
+								ad := []byte(`{"type":"response.function_call_arguments.delta","sequence_number":0,"item_id":"","output_index":0,"delta":""}`)
+								ad, _ = sjson.SetBytes(ad, "sequence_number", nextSeq())
+								ad, _ = sjson.SetBytes(ad, "item_id", fmt.Sprintf("fc_%s", refCallID))
+								ad, _ = sjson.SetBytes(ad, "output_index", outputIndex)
+								ad, _ = sjson.SetBytes(ad, "delta", args.String())
+								out = append(out, emitRespEvent("response.function_call_arguments.delta", ad))
+							}
+							st.FuncArgsBuf[key].WriteString(args.String())
+						}
+						return true
+					})
 				}
 			}
 
@@ -360,15 +384,10 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 					for i := range st.MsgItemAdded {
 						idxs = append(idxs, i)
 					}
-					for i := 0; i < len(idxs); i++ {
+					sort.Slice(idxs, func(i, j int) bool { return st.MsgOutputIx[idxs[i]] < st.MsgOutputIx[idxs[j]] })
-						for j := i + 1; j < len(idxs); j++ {
-							if idxs[j] < idxs[i] {
-								idxs[i], idxs[j] = idxs[j], idxs[i]
-							}
-						}
-					}
 					for _, i := range idxs {
 						if st.MsgItemAdded[i] && !st.MsgItemDone[i] {
+							msgOutputIndex := st.MsgOutputIx[i]
 							fullText := ""
 							if b := st.MsgTextBuf[i]; b != nil {
 								fullText = b.String()
@@ -376,7 +395,7 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 							done := []byte(`{"type":"response.output_text.done","sequence_number":0,"item_id":"","output_index":0,"content_index":0,"text":"","logprobs":[]}`)
 							done, _ = sjson.SetBytes(done, "sequence_number", nextSeq())
 							done, _ = sjson.SetBytes(done, "item_id", fmt.Sprintf("msg_%s_%d", st.ResponseID, i))
-							done, _ = sjson.SetBytes(done, "output_index", i)
+							done, _ = sjson.SetBytes(done, "output_index", msgOutputIndex)
 							done, _ = sjson.SetBytes(done, "content_index", 0)
 							done, _ = sjson.SetBytes(done, "text", fullText)
 							out = append(out, emitRespEvent("response.output_text.done", done))
@@ -384,14 +403,14 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 							partDone := []byte(`{"type":"response.content_part.done","sequence_number":0,"item_id":"","output_index":0,"content_index":0,"part":{"type":"output_text","annotations":[],"logprobs":[],"text":""}}`)
 							partDone, _ = sjson.SetBytes(partDone, "sequence_number", nextSeq())
 							partDone, _ = sjson.SetBytes(partDone, "item_id", fmt.Sprintf("msg_%s_%d", st.ResponseID, i))
-							partDone, _ = sjson.SetBytes(partDone, "output_index", i)
+							partDone, _ = sjson.SetBytes(partDone, "output_index", msgOutputIndex)
 							partDone, _ = sjson.SetBytes(partDone, "content_index", 0)
 							partDone, _ = sjson.SetBytes(partDone, "part.text", fullText)
 							out = append(out, emitRespEvent("response.content_part.done", partDone))
 
 							itemDone := []byte(`{"type":"response.output_item.done","sequence_number":0,"output_index":0,"item":{"id":"","type":"message","status":"completed","content":[{"type":"output_text","annotations":[],"logprobs":[],"text":""}],"role":"assistant"}}`)
 							itemDone, _ = sjson.SetBytes(itemDone, "sequence_number", nextSeq())
-							itemDone, _ = sjson.SetBytes(itemDone, "output_index", i)
+							itemDone, _ = sjson.SetBytes(itemDone, "output_index", msgOutputIndex)
 							itemDone, _ = sjson.SetBytes(itemDone, "item.id", fmt.Sprintf("msg_%s_%d", st.ResponseID, i))
 							itemDone, _ = sjson.SetBytes(itemDone, "item.content.0.text", fullText)
 							out = append(out, emitRespEvent("response.output_item.done", itemDone))
@@ -407,43 +426,42 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 
 				// Emit function call done events for any active function calls
 				if len(st.FuncCallIDs) > 0 {
-					idxs := make([]int, 0, len(st.FuncCallIDs))
+					keys := make([]string, 0, len(st.FuncCallIDs))
-					for i := range st.FuncCallIDs {
+					for key := range st.FuncCallIDs {
-						idxs = append(idxs, i)
+						keys = append(keys, key)
 					}
-					for i := 0; i < len(idxs); i++ {
+					sort.Slice(keys, func(i, j int) bool {
-						for j := i + 1; j < len(idxs); j++ {
+						left := st.FuncOutputIx[keys[i]]
-							if idxs[j] < idxs[i] {
+						right := st.FuncOutputIx[keys[j]]
-								idxs[i], idxs[j] = idxs[j], idxs[i]
+						return left < right || (left == right && keys[i] < keys[j])
-							}
+					})
-						}
+					for _, key := range keys {
-					}
+						callID := st.FuncCallIDs[key]
-					for _, i := range idxs {
+						if callID == "" || st.FuncItemDone[key] {
-						callID := st.FuncCallIDs[i]
-						if callID == "" || st.FuncItemDone[i] {
 							continue
 						}
+						outputIndex := st.FuncOutputIx[key]
 						args := "{}"
-						if b := st.FuncArgsBuf[i]; b != nil && b.Len() > 0 {
+						if b := st.FuncArgsBuf[key]; b != nil && b.Len() > 0 {
 							args = b.String()
 						}
 						fcDone := []byte(`{"type":"response.function_call_arguments.done","sequence_number":0,"item_id":"","output_index":0,"arguments":""}`)
 						fcDone, _ = sjson.SetBytes(fcDone, "sequence_number", nextSeq())
 						fcDone, _ = sjson.SetBytes(fcDone, "item_id", fmt.Sprintf("fc_%s", callID))
-						fcDone, _ = sjson.SetBytes(fcDone, "output_index", i)
+						fcDone, _ = sjson.SetBytes(fcDone, "output_index", outputIndex)
 						fcDone, _ = sjson.SetBytes(fcDone, "arguments", args)
 						out = append(out, emitRespEvent("response.function_call_arguments.done", fcDone))
 
 						itemDone := []byte(`{"type":"response.output_item.done","sequence_number":0,"output_index":0,"item":{"id":"","type":"function_call","status":"completed","arguments":"","call_id":"","name":""}}`)
 						itemDone, _ = sjson.SetBytes(itemDone, "sequence_number", nextSeq())
-						itemDone, _ = sjson.SetBytes(itemDone, "output_index", i)
+						itemDone, _ = sjson.SetBytes(itemDone, "output_index", outputIndex)
 						itemDone, _ = sjson.SetBytes(itemDone, "item.id", fmt.Sprintf("fc_%s", callID))
 						itemDone, _ = sjson.SetBytes(itemDone, "item.arguments", args)
 						itemDone, _ = sjson.SetBytes(itemDone, "item.call_id", callID)
-						itemDone, _ = sjson.SetBytes(itemDone, "item.name", st.FuncNames[i])
+						itemDone, _ = sjson.SetBytes(itemDone, "item.name", st.FuncNames[key])
 						out = append(out, emitRespEvent("response.output_item.done", itemDone))
-						st.FuncItemDone[i] = true
+						st.FuncItemDone[key] = true
-						st.FuncArgsDone[i] = true
+						st.FuncArgsDone[key] = true
 					}
 				}
 				completed := []byte(`{"type":"response.completed","sequence_number":0,"response":{"id":"","object":"response","created_at":0,"status":"completed","background":false,"error":null}}`)
@@ -516,28 +534,21 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 				}
 				// Build response.output using aggregated buffers
 				outputsWrapper := []byte(`{"arr":[]}`)
+				type completedOutputItem struct {
+					index int
+					raw   []byte
+				}
+				outputItems := make([]completedOutputItem, 0, len(st.Reasonings)+len(st.MsgItemAdded)+len(st.FuncArgsBuf))
 				if len(st.Reasonings) > 0 {
 					for _, r := range st.Reasonings {
 						item := []byte(`{"id":"","type":"reasoning","summary":[{"type":"summary_text","text":""}]}`)
 						item, _ = sjson.SetBytes(item, "id", r.ReasoningID)
 						item, _ = sjson.SetBytes(item, "summary.0.text", r.ReasoningData)
-						outputsWrapper, _ = sjson.SetRawBytes(outputsWrapper, "arr.-1", item)
+						outputItems = append(outputItems, completedOutputItem{index: r.OutputIndex, raw: item})
 					}
 				}
-				// Append message items in ascending index order
 				if len(st.MsgItemAdded) > 0 {
-					midxs := make([]int, 0, len(st.MsgItemAdded))
 					for i := range st.MsgItemAdded {
-						midxs = append(midxs, i)
-					}
-					for i := 0; i < len(midxs); i++ {
-						for j := i + 1; j < len(midxs); j++ {
-							if midxs[j] < midxs[i] {
-								midxs[i], midxs[j] = midxs[j], midxs[i]
-							}
-						}
-					}
-					for _, i := range midxs {
 						txt := ""
 						if b := st.MsgTextBuf[i]; b != nil {
 							txt = b.String()
@@ -545,37 +556,29 @@ func ConvertOpenAIChatCompletionsResponseToOpenAIResponses(ctx context.Context,
 						item := []byte(`{"id":"","type":"message","status":"completed","content":[{"type":"output_text","annotations":[],"logprobs":[],"text":""}],"role":"assistant"}`)
 						item, _ = sjson.SetBytes(item, "id", fmt.Sprintf("msg_%s_%d", st.ResponseID, i))
 						item, _ = sjson.SetBytes(item, "content.0.text", txt)
-						outputsWrapper, _ = sjson.SetRawBytes(outputsWrapper, "arr.-1", item)
+						outputItems = append(outputItems, completedOutputItem{index: st.MsgOutputIx[i], raw: item})
 					}
 				}
 				if len(st.FuncArgsBuf) > 0 {
-					idxs := make([]int, 0, len(st.FuncArgsBuf))
+					for key := range st.FuncArgsBuf {
-					for i := range st.FuncArgsBuf {
-						idxs = append(idxs, i)
-					}
-					// small-N sort without extra imports
-					for i := 0; i < len(idxs); i++ {
-						for j := i + 1; j < len(idxs); j++ {
-							if idxs[j] < idxs[i] {
-								idxs[i], idxs[j] = idxs[j], idxs[i]
-							}
-						}
-					}
-					for _, i := range idxs {
 						args := ""
-						if b := st.FuncArgsBuf[i]; b != nil {
+						if b := st.FuncArgsBuf[key]; b != nil {
 							args = b.String()
 						}
-						callID := st.FuncCallIDs[i]
+						callID := st.FuncCallIDs[key]
-						name := st.FuncNames[i]
+						name := st.FuncNames[key]
 						item := []byte(`{"id":"","type":"function_call","status":"completed","arguments":"","call_id":"","name":""}`)
 						item, _ = sjson.SetBytes(item, "id", fmt.Sprintf("fc_%s", callID))
 						item, _ = sjson.SetBytes(item, "arguments", args)
 						item, _ = sjson.SetBytes(item, "call_id", callID)
 						item, _ = sjson.SetBytes(item, "name", name)
-						outputsWrapper, _ = sjson.SetRawBytes(outputsWrapper, "arr.-1", item)
+						outputItems = append(outputItems, completedOutputItem{index: st.FuncOutputIx[key], raw: item})
 					}
 				}
+				sort.Slice(outputItems, func(i, j int) bool { return outputItems[i].index < outputItems[j].index })
+				for _, item := range outputItems {
+					outputsWrapper, _ = sjson.SetRawBytes(outputsWrapper, "arr.-1", item.raw)
+				}
 				if gjson.GetBytes(outputsWrapper, "arr.#").Int() > 0 {
 					completed, _ = sjson.SetRawBytes(completed, "response.output", []byte(gjson.GetBytes(outputsWrapper, "arr").Raw))
 				}

internal/translator/openai/openai/responses/openai_openai-responses_response_test.go

@@ -0,0 +1,305 @@
+package responses
+
+import (
+	"context"
+	"strings"
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func parseOpenAIResponsesSSEEvent(t *testing.T, chunk []byte) (string, gjson.Result) {
+	t.Helper()
+
+	lines := strings.Split(string(chunk), "\n")
+	if len(lines) < 2 {
+		t.Fatalf("unexpected SSE chunk: %q", chunk)
+	}
+
+	event := strings.TrimSpace(strings.TrimPrefix(lines[0], "event:"))
+	dataLine := strings.TrimSpace(strings.TrimPrefix(lines[1], "data:"))
+	if !gjson.Valid(dataLine) {
+		t.Fatalf("invalid SSE data JSON: %q", dataLine)
+	}
+	return event, gjson.Parse(dataLine)
+}
+
+func TestConvertOpenAIChatCompletionsResponseToOpenAIResponses_MultipleToolCallsRemainSeparate(t *testing.T) {
+	in := []string{
+		`data: {"id":"resp_test","object":"chat.completion.chunk","created":1773896263,"model":"model","choices":[{"index":0,"delta":{"role":"assistant","content":null,"reasoning_content":null,"tool_calls":[{"index":0,"id":"call_read","type":"function","function":{"name":"read","arguments":""}}]},"finish_reason":null}]}`,
+		`data: {"id":"resp_test","object":"chat.completion.chunk","created":1773896263,"model":"model","choices":[{"index":0,"delta":{"role":null,"content":null,"reasoning_content":null,"tool_calls":[{"index":0,"function":{"arguments":"{\"filePath\":\"C:\\\\repo\",\"limit\":400,\"offset\":1}"}}]},"finish_reason":null}]}`,
+		`data: {"id":"resp_test","object":"chat.completion.chunk","created":1773896263,"model":"model","choices":[{"index":0,"delta":{"role":"assistant","content":null,"reasoning_content":null,"tool_calls":[{"index":1,"id":"call_glob","type":"function","function":{"name":"glob","arguments":""}}]},"finish_reason":null}]}`,
+		`data: {"id":"resp_test","object":"chat.completion.chunk","created":1773896263,"model":"model","choices":[{"index":0,"delta":{"role":null,"content":null,"reasoning_content":null,"tool_calls":[{"index":1,"function":{"arguments":"{\"path\":\"C:\\\\repo\",\"pattern\":\"*.{yml,yaml}\"}"}}]},"finish_reason":null}]}`,
+		`data: {"id":"resp_test","object":"chat.completion.chunk","created":1773896263,"model":"model","choices":[{"index":0,"delta":{"role":null,"content":null,"reasoning_content":null,"tool_calls":null},"finish_reason":"tool_calls"}],"usage":{"completion_tokens":10,"total_tokens":20,"prompt_tokens":10}}`,
+	}
+
+	request := []byte(`{"model":"gpt-5.4","tool_choice":"auto","parallel_tool_calls":true}`)
+
+	var param any
+	var out [][]byte
+	for _, line := range in {
+		out = append(out, ConvertOpenAIChatCompletionsResponseToOpenAIResponses(context.Background(), "model", request, request, []byte(line), &param)...)
+	}
+
+	addedNames := map[string]string{}
+	doneArgs := map[string]string{}
+	doneNames := map[string]string{}
+	outputItems := map[string]gjson.Result{}
+
+	for _, chunk := range out {
+		ev, data := parseOpenAIResponsesSSEEvent(t, chunk)
+		switch ev {
+		case "response.output_item.added":
+			if data.Get("item.type").String() != "function_call" {
+				continue
+			}
+			addedNames[data.Get("item.call_id").String()] = data.Get("item.name").String()
+		case "response.output_item.done":
+			if data.Get("item.type").String() != "function_call" {
+				continue
+			}
+			callID := data.Get("item.call_id").String()
+			doneArgs[callID] = data.Get("item.arguments").String()
+			doneNames[callID] = data.Get("item.name").String()
+		case "response.completed":
+			output := data.Get("response.output")
+			for _, item := range output.Array() {
+				if item.Get("type").String() == "function_call" {
+					outputItems[item.Get("call_id").String()] = item
+				}
+			}
+		}
+	}
+
+	if len(addedNames) != 2 {
+		t.Fatalf("expected 2 function_call added events, got %d", len(addedNames))
+	}
+	if len(doneArgs) != 2 {
+		t.Fatalf("expected 2 function_call done events, got %d", len(doneArgs))
+	}
+
+	if addedNames["call_read"] != "read" {
+		t.Fatalf("unexpected added name for call_read: %q", addedNames["call_read"])
+	}
+	if addedNames["call_glob"] != "glob" {
+		t.Fatalf("unexpected added name for call_glob: %q", addedNames["call_glob"])
+	}
+
+	if !gjson.Valid(doneArgs["call_read"]) {
+		t.Fatalf("invalid JSON args for call_read: %q", doneArgs["call_read"])
+	}
+	if !gjson.Valid(doneArgs["call_glob"]) {
+		t.Fatalf("invalid JSON args for call_glob: %q", doneArgs["call_glob"])
+	}
+	if strings.Contains(doneArgs["call_read"], "}{") {
+		t.Fatalf("call_read args were concatenated: %q", doneArgs["call_read"])
+	}
+	if strings.Contains(doneArgs["call_glob"], "}{") {
+		t.Fatalf("call_glob args were concatenated: %q", doneArgs["call_glob"])
+	}
+
+	if doneNames["call_read"] != "read" {
+		t.Fatalf("unexpected done name for call_read: %q", doneNames["call_read"])
+	}
+	if doneNames["call_glob"] != "glob" {
+		t.Fatalf("unexpected done name for call_glob: %q", doneNames["call_glob"])
+	}
+
+	if got := gjson.Get(doneArgs["call_read"], "filePath").String(); got != `C:\repo` {
+		t.Fatalf("unexpected filePath for call_read: %q", got)
+	}
+	if got := gjson.Get(doneArgs["call_glob"], "path").String(); got != `C:\repo` {
+		t.Fatalf("unexpected path for call_glob: %q", got)
+	}
+	if got := gjson.Get(doneArgs["call_glob"], "pattern").String(); got != "*.{yml,yaml}" {
+		t.Fatalf("unexpected pattern for call_glob: %q", got)
+	}
+
+	if len(outputItems) != 2 {
+		t.Fatalf("expected 2 function_call items in response.output, got %d", len(outputItems))
+	}
+	if outputItems["call_read"].Get("name").String() != "read" {
+		t.Fatalf("unexpected response.output name for call_read: %q", outputItems["call_read"].Get("name").String())
+	}
+	if outputItems["call_glob"].Get("name").String() != "glob" {
+		t.Fatalf("unexpected response.output name for call_glob: %q", outputItems["call_glob"].Get("name").String())
+	}
+}
+
+func TestConvertOpenAIChatCompletionsResponseToOpenAIResponses_MultiChoiceToolCallsUseDistinctOutputIndexes(t *testing.T) {
+	in := []string{
+		`data: {"id":"resp_multi_choice","object":"chat.completion.chunk","created":1773896263,"model":"model","choices":[{"index":0,"delta":{"role":"assistant","content":null,"reasoning_content":null,"tool_calls":[{"index":0,"id":"call_choice0","type":"function","function":{"name":"glob","arguments":""}}]},"finish_reason":null},{"index":1,"delta":{"role":"assistant","content":null,"reasoning_content":null,"tool_calls":[{"index":0,"id":"call_choice1","type":"function","function":{"name":"read","arguments":""}}]},"finish_reason":null}]}`,
+		`data: {"id":"resp_multi_choice","object":"chat.completion.chunk","created":1773896263,"model":"model","choices":[{"index":0,"delta":{"role":null,"content":null,"reasoning_content":null,"tool_calls":[{"index":0,"function":{"arguments":"{\"path\":\"C:\\\\repo\",\"pattern\":\"*.go\"}"}}]},"finish_reason":null},{"index":1,"delta":{"role":null,"content":null,"reasoning_content":null,"tool_calls":[{"index":0,"function":{"arguments":"{\"filePath\":\"C:\\\\repo\\\\README.md\",\"limit\":20,\"offset\":1}"}}]},"finish_reason":null}]}`,
+		`data: {"id":"resp_multi_choice","object":"chat.completion.chunk","created":1773896263,"model":"model","choices":[{"index":0,"delta":{"role":null,"content":null,"reasoning_content":null,"tool_calls":null},"finish_reason":"tool_calls"},{"index":1,"delta":{"role":null,"content":null,"reasoning_content":null,"tool_calls":null},"finish_reason":"tool_calls"}],"usage":{"completion_tokens":10,"total_tokens":20,"prompt_tokens":10}}`,
+	}
+
+	request := []byte(`{"model":"gpt-5.4","tool_choice":"auto","parallel_tool_calls":true}`)
+
+	var param any
+	var out [][]byte
+	for _, line := range in {
+		out = append(out, ConvertOpenAIChatCompletionsResponseToOpenAIResponses(context.Background(), "model", request, request, []byte(line), &param)...)
+	}
+
+	type fcEvent struct {
+		outputIndex int64
+		name        string
+		arguments   string
+	}
+
+	added := map[string]fcEvent{}
+	done := map[string]fcEvent{}
+
+	for _, chunk := range out {
+		ev, data := parseOpenAIResponsesSSEEvent(t, chunk)
+		switch ev {
+		case "response.output_item.added":
+			if data.Get("item.type").String() != "function_call" {
+				continue
+			}
+			callID := data.Get("item.call_id").String()
+			added[callID] = fcEvent{
+				outputIndex: data.Get("output_index").Int(),
+				name:        data.Get("item.name").String(),
+			}
+		case "response.output_item.done":
+			if data.Get("item.type").String() != "function_call" {
+				continue
+			}
+			callID := data.Get("item.call_id").String()
+			done[callID] = fcEvent{
+				outputIndex: data.Get("output_index").Int(),
+				name:        data.Get("item.name").String(),
+				arguments:   data.Get("item.arguments").String(),
+			}
+		}
+	}
+
+	if len(added) != 2 {
+		t.Fatalf("expected 2 function_call added events, got %d", len(added))
+	}
+	if len(done) != 2 {
+		t.Fatalf("expected 2 function_call done events, got %d", len(done))
+	}
+
+	if added["call_choice0"].name != "glob" {
+		t.Fatalf("unexpected added name for call_choice0: %q", added["call_choice0"].name)
+	}
+	if added["call_choice1"].name != "read" {
+		t.Fatalf("unexpected added name for call_choice1: %q", added["call_choice1"].name)
+	}
+	if added["call_choice0"].outputIndex == added["call_choice1"].outputIndex {
+		t.Fatalf("expected distinct output indexes for different choices, both got %d", added["call_choice0"].outputIndex)
+	}
+
+	if !gjson.Valid(done["call_choice0"].arguments) {
+		t.Fatalf("invalid JSON args for call_choice0: %q", done["call_choice0"].arguments)
+	}
+	if !gjson.Valid(done["call_choice1"].arguments) {
+		t.Fatalf("invalid JSON args for call_choice1: %q", done["call_choice1"].arguments)
+	}
+	if done["call_choice0"].outputIndex == done["call_choice1"].outputIndex {
+		t.Fatalf("expected distinct done output indexes for different choices, both got %d", done["call_choice0"].outputIndex)
+	}
+	if done["call_choice0"].name != "glob" {
+		t.Fatalf("unexpected done name for call_choice0: %q", done["call_choice0"].name)
+	}
+	if done["call_choice1"].name != "read" {
+		t.Fatalf("unexpected done name for call_choice1: %q", done["call_choice1"].name)
+	}
+}
+
+func TestConvertOpenAIChatCompletionsResponseToOpenAIResponses_MixedMessageAndToolUseDistinctOutputIndexes(t *testing.T) {
+	in := []string{
+		`data: {"id":"resp_mixed","object":"chat.completion.chunk","created":1773896263,"model":"model","choices":[{"index":0,"delta":{"role":"assistant","content":"hello","reasoning_content":null,"tool_calls":null},"finish_reason":null},{"index":1,"delta":{"role":"assistant","content":null,"reasoning_content":null,"tool_calls":[{"index":0,"id":"call_choice1","type":"function","function":{"name":"read","arguments":""}}]},"finish_reason":null}]}`,
+		`data: {"id":"resp_mixed","object":"chat.completion.chunk","created":1773896263,"model":"model","choices":[{"index":0,"delta":{"role":null,"content":null,"reasoning_content":null,"tool_calls":null},"finish_reason":"stop"},{"index":1,"delta":{"role":null,"content":null,"reasoning_content":null,"tool_calls":[{"index":0,"function":{"arguments":"{\"filePath\":\"C:\\\\repo\\\\README.md\",\"limit\":20,\"offset\":1}"}}]},"finish_reason":"tool_calls"}],"usage":{"completion_tokens":10,"total_tokens":20,"prompt_tokens":10}}`,
+	}
+
+	request := []byte(`{"model":"gpt-5.4","tool_choice":"auto","parallel_tool_calls":true}`)
+
+	var param any
+	var out [][]byte
+	for _, line := range in {
+		out = append(out, ConvertOpenAIChatCompletionsResponseToOpenAIResponses(context.Background(), "model", request, request, []byte(line), &param)...)
+	}
+
+	var messageOutputIndex int64 = -1
+	var toolOutputIndex int64 = -1
+
+	for _, chunk := range out {
+		ev, data := parseOpenAIResponsesSSEEvent(t, chunk)
+		if ev != "response.output_item.added" {
+			continue
+		}
+		switch data.Get("item.type").String() {
+		case "message":
+			if data.Get("item.id").String() == "msg_resp_mixed_0" {
+				messageOutputIndex = data.Get("output_index").Int()
+			}
+		case "function_call":
+			if data.Get("item.call_id").String() == "call_choice1" {
+				toolOutputIndex = data.Get("output_index").Int()
+			}
+		}
+	}
+
+	if messageOutputIndex < 0 {
+		t.Fatal("did not find message output index")
+	}
+	if toolOutputIndex < 0 {
+		t.Fatal("did not find tool output index")
+	}
+	if messageOutputIndex == toolOutputIndex {
+		t.Fatalf("expected distinct output indexes for message and tool call, both got %d", messageOutputIndex)
+	}
+}
+
+func TestConvertOpenAIChatCompletionsResponseToOpenAIResponses_FunctionCallDoneAndCompletedOutputStayAscending(t *testing.T) {
+	in := []string{
+		`data: {"id":"resp_order","object":"chat.completion.chunk","created":1773896263,"model":"model","choices":[{"index":0,"delta":{"role":"assistant","content":null,"reasoning_content":null,"tool_calls":[{"index":0,"id":"call_glob","type":"function","function":{"name":"glob","arguments":""}}]},"finish_reason":null}]}`,
+		`data: {"id":"resp_order","object":"chat.completion.chunk","created":1773896263,"model":"model","choices":[{"index":0,"delta":{"role":null,"content":null,"reasoning_content":null,"tool_calls":[{"index":0,"function":{"arguments":"{\"path\":\"C:\\\\repo\",\"pattern\":\"*.go\"}"}}]},"finish_reason":null}]}`,
+		`data: {"id":"resp_order","object":"chat.completion.chunk","created":1773896263,"model":"model","choices":[{"index":0,"delta":{"role":"assistant","content":null,"reasoning_content":null,"tool_calls":[{"index":1,"id":"call_read","type":"function","function":{"name":"read","arguments":""}}]},"finish_reason":null}]}`,
+		`data: {"id":"resp_order","object":"chat.completion.chunk","created":1773896263,"model":"model","choices":[{"index":0,"delta":{"role":null,"content":null,"reasoning_content":null,"tool_calls":[{"index":1,"function":{"arguments":"{\"filePath\":\"C:\\\\repo\\\\README.md\",\"limit\":20,\"offset\":1}"}}]},"finish_reason":null}]}`,
+		`data: {"id":"resp_order","object":"chat.completion.chunk","created":1773896263,"model":"model","choices":[{"index":0,"delta":{"role":null,"content":null,"reasoning_content":null,"tool_calls":null},"finish_reason":"tool_calls"}],"usage":{"completion_tokens":10,"total_tokens":20,"prompt_tokens":10}}`,
+	}
+
+	request := []byte(`{"model":"gpt-5.4","tool_choice":"auto","parallel_tool_calls":true}`)
+
+	var param any
+	var out [][]byte
+	for _, line := range in {
+		out = append(out, ConvertOpenAIChatCompletionsResponseToOpenAIResponses(context.Background(), "model", request, request, []byte(line), &param)...)
+	}
+
+	var doneIndexes []int64
+	var completedOrder []string
+
+	for _, chunk := range out {
+		ev, data := parseOpenAIResponsesSSEEvent(t, chunk)
+		switch ev {
+		case "response.output_item.done":
+			if data.Get("item.type").String() == "function_call" {
+				doneIndexes = append(doneIndexes, data.Get("output_index").Int())
+			}
+		case "response.completed":
+			for _, item := range data.Get("response.output").Array() {
+				if item.Get("type").String() == "function_call" {
+					completedOrder = append(completedOrder, item.Get("call_id").String())
+				}
+			}
+		}
+	}
+
+	if len(doneIndexes) != 2 {
+		t.Fatalf("expected 2 function_call done indexes, got %d", len(doneIndexes))
+	}
+	if doneIndexes[0] >= doneIndexes[1] {
+		t.Fatalf("expected ascending done output indexes, got %v", doneIndexes)
+	}
+	if len(completedOrder) != 2 {
+		t.Fatalf("expected 2 function_call items in completed output, got %d", len(completedOrder))
+	}
+	if completedOrder[0] != "call_glob" || completedOrder[1] != "call_read" {
+		t.Fatalf("unexpected completed function_call order: %v", completedOrder)
+	}
+}