fix: backfill empty functionResponse.name from preceding functionCall

when Amp or Claude Code sends functionResponse with an empty name in Gemini
conversation history, the Gemini API rejects the request with 400
"Name cannot be empty". this fix backfills empty names from the
corresponding preceding functionCall parts using positional matching.

covers all three Gemini translator paths:
- gemini/gemini (direct API key)
- antigravity/gemini (OAuth)
- gemini-cli/gemini (Gemini CLI)

also switches fixCLIToolResponse pending group matching from LIFO to
FIFO to correctly handle multiple sequential tool call groups.

fixes #1903

internal/translator/antigravity/gemini/antigravity_gemini_request.go

@@ -138,20 +138,31 @@ func ConvertGeminiRequestToAntigravity(modelName string, inputRawJSON []byte, _
 // FunctionCallGroup represents a group of function calls and their responses
 type FunctionCallGroup struct {
 	ResponsesNeeded int
+	CallNames       []string // ordered function call names for backfilling empty response names
 }
 
 // parseFunctionResponseRaw attempts to normalize a function response part into a JSON object string.
 // Falls back to a minimal "functionResponse" object when parsing fails.
-func parseFunctionResponseRaw(response gjson.Result) string {
+// fallbackName is used when the response's own name is empty.
+func parseFunctionResponseRaw(response gjson.Result, fallbackName string) string {
 	if response.IsObject() && gjson.Valid(response.Raw) {
-		return response.Raw
+		raw := response.Raw
+		name := response.Get("functionResponse.name").String()
+		if strings.TrimSpace(name) == "" && fallbackName != "" {
+			raw, _ = sjson.Set(raw, "functionResponse.name", fallbackName)
+		}
+		return raw
 	}
 
 	log.Debugf("parse function response failed, using fallback")
 	funcResp := response.Get("functionResponse")
 	if funcResp.Exists() {
 		fr := `{"functionResponse":{"name":"","response":{"result":""}}}`
-		fr, _ = sjson.Set(fr, "functionResponse.name", funcResp.Get("name").String())
+		name := funcResp.Get("name").String()
+		if strings.TrimSpace(name) == "" {
+			name = fallbackName
+		}
+		fr, _ = sjson.Set(fr, "functionResponse.name", name)
 		fr, _ = sjson.Set(fr, "functionResponse.response.result", funcResp.Get("response").String())
 		if id := funcResp.Get("id").String(); id != "" {
 			fr, _ = sjson.Set(fr, "functionResponse.id", id)
@@ -159,7 +170,12 @@ func parseFunctionResponseRaw(response gjson.Result) string {
 		return fr
 	}
 
-	fr := `{"functionResponse":{"name":"unknown","response":{"result":""}}}`
+	useName := fallbackName
+	if useName == "" {
+		useName = "unknown"
+	}
+	fr := `{"functionResponse":{"name":"","response":{"result":""}}}`
+	fr, _ = sjson.Set(fr, "functionResponse.name", useName)
 	fr, _ = sjson.Set(fr, "functionResponse.response.result", response.String())
 	return fr
 }
@@ -211,30 +227,26 @@ func fixCLIToolResponse(input string) (string, error) {
 		if len(responsePartsInThisContent) > 0 {
 			collectedResponses = append(collectedResponses, responsePartsInThisContent...)
 
-			// Check if any pending groups can be satisfied
-			for i := len(pendingGroups) - 1; i >= 0; i-- {
-				group := pendingGroups[i]
-				if len(collectedResponses) >= group.ResponsesNeeded {
-					// Take the needed responses for this group
-					groupResponses := collectedResponses[:group.ResponsesNeeded]
-					collectedResponses = collectedResponses[group.ResponsesNeeded:]
+			// Check if pending groups can be satisfied (FIFO: oldest group first)
+			for len(pendingGroups) > 0 && len(collectedResponses) >= pendingGroups[0].ResponsesNeeded {
+				group := pendingGroups[0]
+				pendingGroups = pendingGroups[1:]
 
-					// Create merged function response content
-					functionResponseContent := `{"parts":[],"role":"function"}`
-					for _, response := range groupResponses {
-						partRaw := parseFunctionResponseRaw(response)
-						if partRaw != "" {
-							functionResponseContent, _ = sjson.SetRaw(functionResponseContent, "parts.-1", partRaw)
-						}
+				// Take the needed responses for this group
+				groupResponses := collectedResponses[:group.ResponsesNeeded]
+				collectedResponses = collectedResponses[group.ResponsesNeeded:]
+
+				// Create merged function response content
+				functionResponseContent := `{"parts":[],"role":"function"}`
+				for ri, response := range groupResponses {
+					partRaw := parseFunctionResponseRaw(response, group.CallNames[ri])
+					if partRaw != "" {
+						functionResponseContent, _ = sjson.SetRaw(functionResponseContent, "parts.-1", partRaw)
 					}
+				}
 
-					if gjson.Get(functionResponseContent, "parts.#").Int() > 0 {
-						contentsWrapper, _ = sjson.SetRaw(contentsWrapper, "contents.-1", functionResponseContent)
-					}
-
-					// Remove this group as it's been satisfied
-					pendingGroups = append(pendingGroups[:i], pendingGroups[i+1:]...)
-					break
+				if gjson.Get(functionResponseContent, "parts.#").Int() > 0 {
+					contentsWrapper, _ = sjson.SetRaw(contentsWrapper, "contents.-1", functionResponseContent)
 				}
 			}
 
@@ -243,15 +255,15 @@ func fixCLIToolResponse(input string) (string, error) {
 
 		// If this is a model with function calls, create a new group
 		if role == "model" {
-			functionCallsCount := 0
+			var callNames []string
 			parts.ForEach(func(_, part gjson.Result) bool {
 				if part.Get("functionCall").Exists() {
-					functionCallsCount++
+					callNames = append(callNames, part.Get("functionCall.name").String())
 				}
 				return true
 			})
 
-			if functionCallsCount > 0 {
+			if len(callNames) > 0 {
 				// Add the model content
 				if !value.IsObject() {
 					log.Warnf("failed to parse model content")
@@ -261,7 +273,8 @@ func fixCLIToolResponse(input string) (string, error) {
 
 				// Create a new group for tracking responses
 				group := &FunctionCallGroup{
-					ResponsesNeeded: functionCallsCount,
+					ResponsesNeeded: len(callNames),
+					CallNames:       callNames,
 				}
 				pendingGroups = append(pendingGroups, group)
 			} else {
@@ -291,8 +304,12 @@ func fixCLIToolResponse(input string) (string, error) {
 			collectedResponses = collectedResponses[group.ResponsesNeeded:]
 
 			functionResponseContent := `{"parts":[],"role":"function"}`
-			for _, response := range groupResponses {
-				partRaw := parseFunctionResponseRaw(response)
+			for ri, response := range groupResponses {
+				fallbackName := ""
+				if ri < len(group.CallNames) {
+					fallbackName = group.CallNames[ri]
+				}
+				partRaw := parseFunctionResponseRaw(response, fallbackName)
 				if partRaw != "" {
 					functionResponseContent, _ = sjson.SetRaw(functionResponseContent, "parts.-1", partRaw)
 				}