Record tool intent before execution and add file checkpoints

Why: a crash after a tool was about to run left the call unpaired, and workspace writes could not be rewound.
Evidence: GOWORK=off go test ./runtime/ ./runtime/llm/ ./runtime/checkpoint/ ./runtime/telemetry/ ./runtime/tools/ ./runtime/session/ ./adapters/native/
Impact: pending calls rerun only when both the stored and current replay declarations are safe; otherwise the result is an error. Empty fallback lists and a nil checkpoint log keep the previous behavior.
Refs: feature/durable-rewind
Co-authored-by: Cursor <cursoragent@cursor.com>

adapters/native/backend.go

@@ -14,6 +14,7 @@ import (
 
 	"agent-native/exec"
 	"agent-native/runtime"
+	"agent-native/runtime/checkpoint"
 	"agent-native/runtime/filestate"
 	"agent-native/runtime/hooks"
 	"agent-native/runtime/llm"
@@ -39,13 +40,15 @@ type ModelOptions struct {
 
 // ToolOptions 是可选工具装配。nil 字段不注册对应工具。
 type ToolOptions struct {
-	Search      tools.SearchProvider
-	Exec        *tools.ExecConfig
-	Fetch       *tools.FetchConfig
-	MCP         *mcp.Manager
-	SkillsRoots []string
-	Subagent    subagent.Factory
-	HostTools   []tools.Tool
+	Search           tools.SearchProvider
+	Exec             *tools.ExecConfig
+	Fetch            *tools.FetchConfig
+	MCP              *mcp.Manager
+	SkillsRoots      []string
+	Subagent         subagent.Factory
+	HostTools        []tools.Tool
+	Checkpoints      *checkpoint.Log
+	CheckpointAnchor func() string
 }
 
 // SessionOptions 是单次执行的会话预算与压缩。
@@ -58,6 +61,8 @@ type SessionOptions struct {
 type ObserveOptions struct {
 	Log         *logsys.Logger
 	ExecutionID string
+	// Trace 交给运行循环。nil 不采集。
+	Trace func(name string, attrs map[string]string) func()
 }
 
 // GateOptions 把直连已经使用的停止、提醒和工具钩子交给小队成员。零值不改变行为。
@@ -184,7 +189,7 @@ func (b *Backend) Execute(ctx context.Context, req exec.Request) (*exec.Result,
 
 	var reg *tools.Registry
 	if profile == exec.ToolProfileWorkspace {
-		reg = tools.WorkspaceToolsTracked(workDir, filestate.New())
+		reg = tools.WorkspaceToolsCheckpointed(workDir, filestate.New(), b.opts.Checkpoints, b.opts.CheckpointAnchor)
 		skills.RegisterLoader(reg, skillStore)
 		if b.opts.Search != nil {
 			tools.RegisterSearch(reg, b.opts.Search)
@@ -348,6 +353,7 @@ func (b *Backend) run(ctx context.Context, model string, budget *runtime.Budget,
 		Reminders:    b.opts.Reminders,
 		RepeatGuard:  b.opts.RepeatGuard,
 		Hooks:        gateBus(b.opts.GateOptions),
+		Trace:        b.opts.Trace,
 		OnEvent: func(ev runtime.Event) {
 			logs.WriteString(ev.Type)
 			if ev.Tool != "" {