fix(kiro): merge adjacent assistant messages while preserving tool_calls

internal/translator/kiro/common/message_merge.go

@@ -33,18 +33,17 @@ func MergeAdjacentMessages(messages []gjson.Result) []gjson.Result {
 			continue
 		}
 
-		// Don't merge assistant messages that have tool_calls - these must stay separate
-		// so that subsequent tool results can match their tool_call IDs
-		if currentRole == "assistant" && (msg.Get("tool_calls").Exists() || lastMsg.Get("tool_calls").Exists()) {
-			merged = append(merged, msg)
-			continue
-		}
-
 		if currentRole == lastRole {
 			// Merge content from current message into last message
 			mergedContent := mergeMessageContent(lastMsg, msg)
-			// Create a new merged message JSON
-			mergedMsg := createMergedMessage(lastRole, mergedContent)
+			var mergedToolCalls []interface{}
+			if currentRole == "assistant" {
+				// Preserve assistant tool_calls when adjacent assistant messages are merged.
+				mergedToolCalls = mergeToolCalls(lastMsg.Get("tool_calls"), msg.Get("tool_calls"))
+			}
+
+			// Create a new merged message JSON.
+			mergedMsg := createMergedMessage(lastRole, mergedContent, mergedToolCalls)
 			merged[len(merged)-1] = gjson.Parse(mergedMsg)
 		} else {
 			merged = append(merged, msg)
@@ -128,12 +127,34 @@ func blockToMap(block gjson.Result) map[string]interface{} {
 	return result
 }
 
-// createMergedMessage creates a JSON string for a merged message
-func createMergedMessage(role string, content string) string {
+// createMergedMessage creates a JSON string for a merged message.
+// toolCalls is optional and only emitted for assistant role.
+func createMergedMessage(role string, content string, toolCalls []interface{}) string {
 	msg := map[string]interface{}{
 		"role":    role,
 		"content": json.RawMessage(content),
 	}
+	if role == "assistant" && len(toolCalls) > 0 {
+		msg["tool_calls"] = toolCalls
+	}
 	result, _ := json.Marshal(msg)
 	return string(result)
-}
+}
+
+// mergeToolCalls combines tool_calls from two assistant messages while preserving order.
+func mergeToolCalls(tc1, tc2 gjson.Result) []interface{} {
+	var merged []interface{}
+
+	if tc1.IsArray() {
+		for _, tc := range tc1.Array() {
+			merged = append(merged, tc.Value())
+		}
+	}
+	if tc2.IsArray() {
+		for _, tc := range tc2.Array() {
+			merged = append(merged, tc.Value())
+		}
+	}
+
+	return merged
+}

internal/translator/kiro/common/message_merge_test.go

@@ -0,0 +1,106 @@
+package common
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/tidwall/gjson"
+)
+
+func parseMessages(t *testing.T, raw string) []gjson.Result {
+	t.Helper()
+	parsed := gjson.Parse(raw)
+	if !parsed.IsArray() {
+		t.Fatalf("expected JSON array, got: %s", raw)
+	}
+	return parsed.Array()
+}
+
+func TestMergeAdjacentMessages_AssistantMergePreservesToolCalls(t *testing.T) {
+	messages := parseMessages(t, `[
+		{"role":"assistant","content":"part1"},
+		{
+			"role":"assistant",
+			"content":"part2",
+			"tool_calls":[
+				{
+					"id":"call_1",
+					"type":"function",
+					"function":{"name":"Read","arguments":"{}"}
+				}
+			]
+		},
+		{"role":"tool","tool_call_id":"call_1","content":"ok"}
+	]`)
+
+	merged := MergeAdjacentMessages(messages)
+	if len(merged) != 2 {
+		t.Fatalf("expected 2 messages after merge, got %d", len(merged))
+	}
+
+	assistant := merged[0]
+	if assistant.Get("role").String() != "assistant" {
+		t.Fatalf("expected first message role assistant, got %q", assistant.Get("role").String())
+	}
+
+	toolCalls := assistant.Get("tool_calls")
+	if !toolCalls.IsArray() || len(toolCalls.Array()) != 1 {
+		t.Fatalf("expected assistant.tool_calls length 1, got: %s", toolCalls.Raw)
+	}
+	if toolCalls.Array()[0].Get("id").String() != "call_1" {
+		t.Fatalf("expected tool call id call_1, got %q", toolCalls.Array()[0].Get("id").String())
+	}
+
+	contentRaw := assistant.Get("content").Raw
+	if !strings.Contains(contentRaw, "part1") || !strings.Contains(contentRaw, "part2") {
+		t.Fatalf("expected merged content to contain both parts, got: %s", contentRaw)
+	}
+
+	if merged[1].Get("role").String() != "tool" {
+		t.Fatalf("expected second message role tool, got %q", merged[1].Get("role").String())
+	}
+}
+
+func TestMergeAdjacentMessages_AssistantMergeCombinesMultipleToolCalls(t *testing.T) {
+	messages := parseMessages(t, `[
+		{
+			"role":"assistant",
+			"content":"first",
+			"tool_calls":[
+				{"id":"call_1","type":"function","function":{"name":"Read","arguments":"{}"}}
+			]
+		},
+		{
+			"role":"assistant",
+			"content":"second",
+			"tool_calls":[
+				{"id":"call_2","type":"function","function":{"name":"Write","arguments":"{}"}}
+			]
+		}
+	]`)
+
+	merged := MergeAdjacentMessages(messages)
+	if len(merged) != 1 {
+		t.Fatalf("expected 1 message after merge, got %d", len(merged))
+	}
+
+	toolCalls := merged[0].Get("tool_calls").Array()
+	if len(toolCalls) != 2 {
+		t.Fatalf("expected 2 merged tool calls, got %d", len(toolCalls))
+	}
+	if toolCalls[0].Get("id").String() != "call_1" || toolCalls[1].Get("id").String() != "call_2" {
+		t.Fatalf("unexpected merged tool call ids: %q, %q", toolCalls[0].Get("id").String(), toolCalls[1].Get("id").String())
+	}
+}
+
+func TestMergeAdjacentMessages_ToolMessagesRemainUnmerged(t *testing.T) {
+	messages := parseMessages(t, `[
+		{"role":"tool","tool_call_id":"call_1","content":"r1"},
+		{"role":"tool","tool_call_id":"call_2","content":"r2"}
+	]`)
+
+	merged := MergeAdjacentMessages(messages)
+	if len(merged) != 2 {
+		t.Fatalf("expected tool messages to remain separate, got %d", len(merged))
+	}
+}