Let hosts register tools and observe token usage

Why: product runners need register_artifact and card tools inside the kernel loop, and the UI needs token usage on the same event stream as text and tool calls.
Evidence: go test ./... in agent-native; TestHostToolAndUsageEvent and TestHostToolNameConflictFailsClosed.
Impact: Options.HostTools fail closed on name clashes; ProcessEvent and runtime events gain a usage type with token counts. Existing callers that ignore unknown event types stay compatible.
Refs: deliverable-quality-system B1
Co-authored-by: Cursor <cursoragent@cursor.com>

adapters/native/backend.go

@@ -50,6 +50,8 @@ type Options struct {
 	Compact *CompactConfig
 	// Subagent 可选：提供时注册 delegate_task（委派由宿主实现，内核只开端口）。
 	Subagent subagent.Factory
+	// HostTools 是宿主产品工具（登记工件、卡片、知识库）。与内核工具同名时失败，不覆盖。
+	HostTools []tools.Tool
 	// Log 可选。nil 时丢弃日志。
 	Log *logsys.Logger
 	// ExecutionID 写入日志，不参与执行控制。
@@ -168,6 +170,12 @@ func (b *Backend) Execute(ctx context.Context, req exec.Request) (*exec.Result,
 			}
 		}
 		subagent.Register(reg, b.opts.Subagent)
+		for _, tool := range b.opts.HostTools {
+			if reg.Has(tool.Name()) {
+				return &exec.Result{Success: false, ErrorReason: "host tool name conflicts with a builtin: " + tool.Name()}, nil
+			}
+			reg.Register(tool)
+		}
 		if err := reg.Restrict(req.ToolAllowlist); err != nil {
 			return &exec.Result{Success: false, ErrorReason: err.Error()}, nil
 		}
@@ -313,10 +321,12 @@ func (b *Backend) run(ctx context.Context, model string, budget *runtime.Budget,
 			logs.WriteByte('\n')
 			if onProcess != nil {
 				onProcess(exec.ProcessEvent{
-					Type:   ev.Type,
-					Text:   ev.Text,
-					Tool:   ev.Tool,
-					Detail: ev.Detail,
+					Type:             ev.Type,
+					Text:             ev.Text,
+					Tool:             ev.Tool,
+					Detail:           ev.Detail,
+					PromptTokens:     ev.PromptTokens,
+					CompletionTokens: ev.CompletionTokens,
 				})
 			}
 		},

adapters/native/host_tools_test.go

@@ -0,0 +1,119 @@
+package native
+
+import (
+	"context"
+	"encoding/json"
+	"sync"
+	"testing"
+
+	"agent-native/exec"
+	"agent-native/runtime/llm"
+	"agent-native/runtime/tools"
+)
+
+type hostTool struct{ name string }
+
+func (h hostTool) Name() string        { return h.name }
+func (h hostTool) Description() string { return "host tool" }
+func (h hostTool) Parameters() json.RawMessage {
+	return json.RawMessage(`{"type":"object","properties":{"path":{"type":"string"}}}`)
+}
+func (h hostTool) Execute(ctx context.Context, args json.RawMessage) (tools.Result, error) {
+	return tools.Result{Content: "registered " + h.name}, nil
+}
+
+func TestHostToolAndUsageEvent(t *testing.T) {
+	var events []exec.ProcessEvent
+	b := New(Options{
+		Model:     "fake",
+		HostTools: []tools.Tool{hostTool{name: "register_artifact"}},
+		Stream:    usageScript(),
+	})
+	res, err := b.Execute(context.Background(), exec.Request{
+		WorkDir: t.TempDir(), Prompt: "登记",
+		OnEvent: func(ev exec.ProcessEvent) { events = append(events, ev) },
+	})
+	if err != nil || !res.Success {
+		t.Fatalf("execute: err=%v res=%+v logs=%s", err, res, logsOf(res))
+	}
+	sawText, sawStart, sawEnd, sawUsage := false, false, false, false
+	for _, ev := range events {
+		switch ev.Type {
+		case "text_delta":
+			if ev.Text != "" {
+				sawText = true
+			}
+		case "tool_execution_start":
+			if ev.Tool == "register_artifact" {
+				sawStart = true
+			}
+		case "tool_execution_end":
+			if ev.Tool == "register_artifact" {
+				sawEnd = true
+			}
+		case "usage":
+			if ev.PromptTokens == 11 && ev.CompletionTokens == 7 {
+				sawUsage = true
+			}
+		}
+	}
+	if !sawText || !sawStart || !sawEnd || !sawUsage {
+		t.Fatalf("events missing text/tool/usage: %+v", events)
+	}
+}
+
+func TestHostToolNameConflictFailsClosed(t *testing.T) {
+	b := New(Options{
+		Model:     "fake",
+		Stream:    script(llm.Message{Role: llm.RoleAssistant, Content: "x", StopReason: llm.StopEnd}),
+		HostTools: []tools.Tool{hostTool{name: "read_file"}},
+	})
+	res, err := b.Execute(context.Background(), exec.Request{
+		WorkDir: t.TempDir(), Prompt: "x", Targets: []string{"output.md"},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if res.Success || res.ErrorReason == "" {
+		t.Fatalf("conflict must fail closed, got %+v", res)
+	}
+}
+
+func usageScript() llm.StreamFunc {
+	var mu sync.Mutex
+	step := 0
+	return func(ctx context.Context, model string, messages []llm.Message, td []llm.ToolDecl, opts llm.StreamOptions) <-chan llm.Event {
+		ch := make(chan llm.Event, 4)
+		go func() {
+			defer close(ch)
+			mu.Lock()
+			defer mu.Unlock()
+			step++
+			switch step {
+			case 1:
+				ch <- llm.Event{Kind: llm.KindMessageEnd, Message: llm.Message{
+					Role: llm.RoleAssistant, StopReason: llm.StopToolCalls,
+					ToolCalls: []llm.ToolCall{{ID: "c1", Name: "register_artifact", Arguments: `{"path":"a.docx"}`}},
+				}, Usage: llm.Usage{PromptTokens: 4, CompletionTokens: 2}}
+			case 2:
+				ch <- llm.Event{Kind: llm.KindMessageEnd, Message: llm.Message{
+					Role: llm.RoleAssistant, StopReason: llm.StopToolCalls,
+					ToolCalls: []llm.ToolCall{{ID: "c2", Name: "write_file", Arguments: `{"path":"output.md","content":"done"}`}},
+				}, Usage: llm.Usage{PromptTokens: 4, CompletionTokens: 2}}
+			default:
+				ch <- llm.Event{Kind: llm.KindTextDelta, Text: "已登记"}
+				ch <- llm.Event{Kind: llm.KindMessageEnd, Message: llm.Message{
+					Role: llm.RoleAssistant, Content: "已登记", StopReason: llm.StopEnd,
+				}, Usage: llm.Usage{PromptTokens: 3, CompletionTokens: 3}}
+			}
+		}()
+		return ch
+	}
+}
+
+func logsOf(res *exec.Result) string {
+	if res == nil {
+		return ""
+	}
+	return res.Logs
+}