feat: AutoZero 通用 Agent 框架（从 AutoGo 五阶段拆分完成）

llm（三协议 Provider）/ session（JSONL 持久化）/ tools（Registry、围栏、
builtin、computer）/ cdp（browser）/ skills / mcp / agent（循环、两级压缩、
编排、审批门控）+ 底座 jsonl/textx/execx/diag/scratch/spill/imagecache。

产品装配代码（config 桥接、schedule 工具、memory/plan/retro/prompt）
留在 AutoGo，宿主接入方式见 MIGRATION.md。

agent/steer_test.go

@@ -0,0 +1,98 @@
+package agent
+
+import (
+	"context"
+	"testing"
+
+	"git.gopher.ink/mirrors2/AutoZero/llm"
+	"git.gopher.ink/mirrors2/AutoZero/tools"
+)
+
+// TestSteerDeliveredAtStepBoundary：插话必须在工具结果回填之后、下一次模型调用
+// 之前落成普通 user 消息；模型下一步就能看到它。
+func TestSteerDeliveredAtStepBoundary(t *testing.T) {
+	calls := 0
+	prov := &scriptedProvider{fn: func(call int, _ string, _ []llm.Message, _ []llm.ToolDef) (llm.Message, error) {
+		calls++
+		if call == 1 {
+			return llm.Message{Role: llm.RoleAssistant, ToolCalls: []llm.ToolCall{
+				{ID: "t1", Name: "noop", Input: "{}"},
+			}}, nil
+		}
+		return llm.Message{Role: llm.RoleAssistant, Content: "done"}, nil
+	}}
+	noop := &tools.Tool{Name: "noop", Run: func(context.Context, string) (tools.Result, error) {
+		return tools.TextResult("ok"), nil
+	}}
+	a, sess := newTestAgent(t, noop)
+	a.Provider = prov
+
+	pending := []SteerMessage{{Text: "also fix the typo"}}
+	a.Opt.Steer = func() []SteerMessage {
+		out := pending
+		pending = nil
+		return out
+	}
+	var steered []SteerMessage
+	a.Opt.OnSteer = func(m SteerMessage) { steered = append(steered, m) }
+
+	if err := a.Run(context.Background(), "do it"); err != nil {
+		t.Fatal(err)
+	}
+	if calls != 2 {
+		t.Fatalf("model calls = %d, want 2", calls)
+	}
+	if len(steered) != 1 || steered[0].Text != "also fix the typo" {
+		t.Fatalf("OnSteer = %+v", steered)
+	}
+	steerAt, toolAt := -1, -1
+	for i, m := range sess.Messages {
+		if m.Role == llm.RoleUser && m.Content == "also fix the typo" {
+			steerAt = i
+		}
+		if m.Role == llm.RoleTool {
+			toolAt = i
+		}
+	}
+	if steerAt < 0 || toolAt < 0 || steerAt < toolAt {
+		t.Fatalf("steer must land after the tool result (tool=%d steer=%d): %+v", toolAt, steerAt, sess.Messages)
+	}
+}
+
+// TestSteerContinuesAnOtherwiseCompletedTurn：模型已经说完了，但宿主还有插话——
+// 不能直接收尾，要把插话落盘再跑一步。这保证"回合结束才发"的旧排队语义也能
+// 在同一回合内被消费，而不是等下一次用户手动发送。
+func TestSteerContinuesAnOtherwiseCompletedTurn(t *testing.T) {
+	calls := 0
+	prov := &scriptedProvider{fn: func(call int, _ string, _ []llm.Message, _ []llm.ToolDef) (llm.Message, error) {
+		calls++
+		if call == 1 {
+			return llm.Message{Role: llm.RoleAssistant, Content: "first done"}, nil
+		}
+		return llm.Message{Role: llm.RoleAssistant, Content: "second done"}, nil
+	}}
+	a, sess := newTestAgent(t)
+	a.Provider = prov
+
+	pending := []SteerMessage{{Text: "one more thing"}}
+	a.Opt.Steer = func() []SteerMessage {
+		out := pending
+		pending = nil
+		return out
+	}
+
+	if err := a.Run(context.Background(), "start"); err != nil {
+		t.Fatal(err)
+	}
+	if calls != 2 {
+		t.Fatalf("model calls = %d, want 2 (the steer must not be dropped)", calls)
+	}
+	if len(sess.Messages) < 4 {
+		t.Fatalf("messages = %+v", sess.Messages)
+	}
+	last := sess.Messages[len(sess.Messages)-1]
+	prev := sess.Messages[len(sess.Messages)-2]
+	if prev.Role != llm.RoleUser || prev.Content != "one more thing" || last.Content != "second done" {
+		t.Fatalf("steer was not answered in the same turn: %+v", sess.Messages)
+	}
+}