fix(loop): 原生工具调用从 Response.ToolCalls 解码 + 逐次回填工具结果 — 修复工具消息无回复

- 根因: loop/agent.decodeToolCalls 只读 resp.Message.ToolCallName/resp.Content JSON信封, 从不看 api 原生解析出的 resp.ToolCalls(Anthropic tool_use / OpenAI tool_calls)
  → 模型返回 thinking+tool_use(无text) 被判定'无工具调用' → 空 Content 当最终 text → res.Text="" → no reply produced; 纯聊天消息不调工具直接出 text, 故表现为'部分消息无回复'
- agent/step.go: ToolCall 增 ID; ExtractToolCalls 导出并优先 resp.ToolCalls(保留原生id+归一化nil Args), 回落两旧约定
- loop/request.go: decodeToolCalls 委托 agent.ExtractToolCalls(流式/非流式共用)
- loop/tool_history.go(新): 原生批次回填 assistant tool_use + 带tool_use_id的tool_result; 旧JSON信封批次保持 RoleTool 纯文本(向后兼容)
- openai.go: tool_call parts 编成 tool_calls + tool_call_id
- 新增 native_toolcall_test + native_toolcall_http_test(httptest假Anthropic SSE: round1 tool_use(无text)→round2含tool_use_id/tool_result→res.Text非空)
- build/vet/test绿+交叉编译

internal/runtime/agent/agent_test.go

@@ -366,8 +366,8 @@ func TestRunStep_ContextCanceled(t *testing.T) {
 
 func TestExtractToolCalls_NonJSONContent(t *testing.T) {
 	t.Parallel()
-	if _, ok := extractToolCalls(model.Response{Content: "plain text"}); ok {
-		t.Fatalf("extractToolCalls(plain) ok = true, want false")
+	if _, ok := ExtractToolCalls(model.Response{Content: "plain text"}); ok {
+		t.Fatalf("ExtractToolCalls(plain) ok = true, want false")
 	}
 }
 

internal/runtime/agent/step.go

@@ -25,6 +25,11 @@ const (
 // ToolCall is a single function call the assistant requested, decoded from a
 // step. Args holds the tool arguments as a JSON object.
 type ToolCall struct {
+	// ID is the provider tool_use/tool_call id, so the loop can feed the result
+	// back as a native tool_result correlated to the exact call (Anthropic
+	// tool_use_id / OpenAI tool_call_id). Empty for the legacy JSON-envelope
+	// convention, where the provider emitted no id.
+	ID   string         `json:"id,omitempty"`
 	Name string         `json:"name"`
 	Args map[string]any `json:"args"`
 }
@@ -95,15 +100,17 @@ func (a *Agent) RunStep(ctx context.Context, sessionID string, messages []model.
 		}
 	}
 
-	if calls, ok := extractToolCalls(resp); ok {
+	if calls, ok := ExtractToolCalls(resp); ok {
 		return &StepResult{Final: false, ToolCalls: calls, StopReason: StopReasonToolCalls}, nil
 	}
 	return &StepResult{Final: true, Text: resp.Content, StopReason: StopReasonStop}, nil
 }
 
-// extractToolCalls decodes tool calls from a model.Response. The current model
-// layer does not parse provider tool_calls into a structured field, so the agent
-// uses two conventions in priority order:
+// ExtractToolCalls decodes tool calls from a model.Response. It prefers the
+// provider-native ToolCalls the adapters populate (Anthropic tool_use / OpenAI
+// tool_calls), which carry the provider id needed to correlate the result and
+// are the only shape a real native-tool provider emits. It then falls back to
+// two legacy conventions used by prompt-engineered providers:
 //
 //  1. The normalized assistant-message placeholder: when resp.Message carries a
 //     ToolCallName it is a single call with no argument payload.
@@ -112,7 +119,10 @@ func (a *Agent) RunStep(ctx context.Context, sessionID string, messages []model.
 //
 // It reports ok=true (with a non-empty slice) when a call is decoded, and
 // ok=false otherwise.
-func extractToolCalls(resp model.Response) ([]ToolCall, bool) {
+func ExtractToolCalls(resp model.Response) ([]ToolCall, bool) {
+	if len(resp.ToolCalls) > 0 {
+		return nativeToolCalls(resp.ToolCalls), true
+	}
 	if resp.Message.Role == model.RoleAssistant && resp.Message.ToolCallName != "" {
 		return []ToolCall{{Name: resp.Message.ToolCallName, Args: map[string]any{}}}, true
 	}
@@ -131,3 +141,18 @@ func extractToolCalls(resp model.Response) ([]ToolCall, bool) {
 	}
 	return payload.ToolCalls, true
 }
+
+// nativeToolCalls converts the adapter-decoded provider tool calls into the
+// agent's ToolCall, preserving the provider id and normalizing a nil Args to an
+// empty object so downstream fingerprinting and invocation never see nil.
+func nativeToolCalls(calls []model.ToolCall) []ToolCall {
+	out := make([]ToolCall, 0, len(calls))
+	for _, c := range calls {
+		args := c.Args
+		if args == nil {
+			args = map[string]any{}
+		}
+		out = append(out, ToolCall{ID: c.ID, Name: c.Name, Args: args})
+	}
+	return out
+}