fix(qoder): pair tool calls whose assistant turn has null content

changelog/unreleased/qoder-null-content-tool-pairing.md

@@ -0,0 +1,7 @@
+### English
+
+- Fix Qoder chat rejecting multi-turn tool use with `400 InvalidParameter: messages with role "tool" must be a response to a preceeding message with "tool_calls"`. The upstream gateway only pairs a `role:"tool"` message with the assistant turn ahead of it when that assistant message's `content` is a string; OpenAI clients send `"content": null` for a pure tool-call turn, which left the call unregistered. The in-process client now rewrites a nil content on a tool-call turn to an empty string, which the gateway accepts. Call ids, tool results, and all other content shapes pass through untouched.
+
+### 中文
+
+- 修复 Qoder 多轮工具调用被上游以 `400 InvalidParameter: messages with role "tool" must be a response to a preceeding message with "tool_calls"` 拒绝的问题。上游网关只在前一条 assistant 消息的 `content` 为字符串时，才把它携带的 `tool_calls` 登记为可配对；OpenAI 客户端对纯工具调用轮次发送的正是 `"content": null`，导致调用未登记、后续 `role:"tool"` 消息被拒。进程内直连客户端现在会把工具调用轮次的 null content 改写为空字符串（网关接受该形状）；工具调用 id、工具结果与其他内容形状均原样保留。

internal/providers/qoder/direct.go

@@ -262,7 +262,7 @@ func BuildPlainChatBody(req translate.ChatRequest, now time.Time) map[string]any
 			}
 			continue
 		}
-		item := map[string]any{"role": message.Role, "content": message.Content}
+		item := map[string]any{"role": message.Role, "content": normalizeMessageContent(message)}
 		if message.Name != "" {
 			item["name"] = message.Name
 		}
@@ -353,6 +353,28 @@ func BuildPlainChatBody(req translate.ChatRequest, now time.Time) map[string]any
 	}
 }
 
+// normalizeMessageContent replaces a nil content on a message that carries
+// tool_calls with an empty string.
+//
+// The gateway pairs each role:"tool" message with the tool_calls of the
+// assistant turn ahead of it, and it only registers that pairing when the
+// assistant message's `content` is a string. A JSON null — what OpenAI clients
+// send for an assistant turn that is pure tool calls — leaves the call
+// unregistered, and the following role:"tool" message is then rejected with
+//
+//	messages with role "tool" must be a response to a preceeding message
+//	with "tool_calls"
+//
+// An empty string is accepted and pairs correctly. Only messages with
+// tool_calls are rewritten; every other content shape passes through
+// untouched.
+func normalizeMessageContent(message translate.ChatMessage) any {
+	if len(message.ToolCalls) > 0 && message.Content == nil {
+		return ""
+	}
+	return message.Content
+}
+
 func rawNumber(raw json.RawMessage) (int, bool) {
 	if len(raw) == 0 {
 		return 0, false

internal/providers/qoder/null_content_test.go

@@ -0,0 +1,115 @@
+package qoder
+
+import (
+	"encoding/json"
+	"testing"
+	"time"
+
+	"github.com/caigee-cmd/cli2api/internal/translate"
+)
+
+// The gateway pairs a role:"tool" message with the tool_calls of the assistant
+// turn ahead of it, and only registers that pairing when the assistant
+// message's content is a string. OpenAI clients send `"content": null` for a
+// pure tool-call turn, which leaves the call unregistered and the gateway
+// rejects the follow-up tool message:
+//
+//	messages with role "tool" must be a response to a preceeding message
+//	with "tool_calls"
+//
+// An empty string pairs correctly, so a nil content on a tool-call turn is
+// rewritten to "".
+func TestBuildPlainChatBodyNullContentWithToolCallsBecomesEmptyString(t *testing.T) {
+	raw := `{
+		"model":"qwen3.8-flash","stream":false,"max_tokens":40,
+		"tools":[{"type":"function","function":{"name":"bash","description":"run","parameters":{"type":"object"}}}],
+		"messages":[
+			{"role":"user","content":"run ls"},
+			{"role":"assistant","content":null,"tool_calls":[{"id":"call_1","type":"function","function":{"name":"bash","arguments":"{}"}}]},
+			{"role":"tool","tool_call_id":"call_1","content":"file1.txt"},
+			{"role":"user","content":"say OK"}
+		]
+	}`
+	var req translate.ChatRequest
+	if err := json.Unmarshal([]byte(raw), &req); err != nil {
+		t.Fatal(err)
+	}
+	plain := BuildPlainChatBody(req, time.Now())
+	encoded, _ := json.Marshal(plain["messages"])
+	t.Logf("messages = %s", encoded)
+
+	var msgs []struct {
+		Role      string          `json:"role"`
+		Content   json.RawMessage `json:"content"`
+		ToolCalls json.RawMessage `json:"tool_calls"`
+	}
+	if err := json.Unmarshal(encoded, &msgs); err != nil {
+		t.Fatal(err)
+	}
+	if len(msgs) != 4 {
+		t.Fatalf("message count = %d, want 4", len(msgs))
+	}
+	if string(msgs[1].Content) != `""` {
+		t.Fatalf("assistant content = %s, want an empty string", msgs[1].Content)
+	}
+	// The tool call and its id must survive the rewrite untouched.
+	if len(msgs[1].ToolCalls) == 0 {
+		t.Fatal("assistant tool_calls dropped")
+	}
+}
+
+// A plain assistant message with null content and no tool calls keeps its
+// original shape: the pairing rule only applies to tool-call turns.
+func TestBuildPlainChatBodyKeepsNullContentWithoutToolCalls(t *testing.T) {
+	raw := `{
+		"model":"qwen3.8-flash","max_tokens":40,
+		"messages":[
+			{"role":"user","content":"hi"},
+			{"role":"assistant","content":null}
+		]
+	}`
+	var req translate.ChatRequest
+	if err := json.Unmarshal([]byte(raw), &req); err != nil {
+		t.Fatal(err)
+	}
+	plain := BuildPlainChatBody(req, time.Now())
+	encoded, _ := json.Marshal(plain["messages"])
+
+	var msgs []struct {
+		Content json.RawMessage `json:"content"`
+	}
+	if err := json.Unmarshal(encoded, &msgs); err != nil {
+		t.Fatal(err)
+	}
+	if string(msgs[1].Content) != "null" {
+		t.Fatalf("content = %s, want null (no tool_calls to pair)", msgs[1].Content)
+	}
+}
+
+// Non-empty content and empty-string content both pass through unchanged.
+func TestBuildPlainChatBodyKeepsExistingContent(t *testing.T) {
+	for _, want := range []string{`""`, `"planning the call"`} {
+		raw := `{
+			"model":"qwen3.8-flash","max_tokens":40,
+			"messages":[
+				{"role":"user","content":"hi"},
+				{"role":"assistant","content":` + want + `,"tool_calls":[{"id":"call_1","type":"function","function":{"name":"bash","arguments":"{}"}}]}
+			]
+		}`
+		var req translate.ChatRequest
+		if err := json.Unmarshal([]byte(raw), &req); err != nil {
+			t.Fatal(err)
+		}
+		plain := BuildPlainChatBody(req, time.Now())
+		encoded, _ := json.Marshal(plain["messages"])
+		var msgs []struct {
+			Content json.RawMessage `json:"content"`
+		}
+		if err := json.Unmarshal(encoded, &msgs); err != nil {
+			t.Fatal(err)
+		}
+		if string(msgs[1].Content) != want {
+			t.Fatalf("content = %s, want %s", msgs[1].Content, want)
+		}
+	}
+}