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。

tools/instructions_test.go

@@ -0,0 +1,103 @@
+package tools
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func writeTree(t *testing.T, root string, files map[string]string) {
+	t.Helper()
+	for name, content := range files {
+		p := filepath.Join(root, name)
+		if err := os.MkdirAll(filepath.Dir(p), 0o755); err != nil {
+			t.Fatal(err)
+		}
+		if err := os.WriteFile(p, []byte(content), 0o644); err != nil {
+			t.Fatal(err)
+		}
+	}
+}
+
+// TestDiscoverNestedInstructions：只发现目标子树到工作区根之间的 AGENTS.md，
+// 根自己的那份跳过（它已在基础 system 提示里）。
+func TestDiscoverNestedInstructions(t *testing.T) {
+	root := t.TempDir()
+	writeTree(t, root, map[string]string{
+		"AGENTS.md":          "ROOT-RULES",
+		"sub/AGENTS.md":      "SUB-RULES",
+		"sub/deep/AGENTS.md": "DEEP-RULES",
+		"sub/deep/x.go":      "package deep",
+	})
+	var got []string
+	discoverInstructions(filepath.Join(root, "sub/deep/x.go"), false, root, func(p, text string) {
+		got = append(got, text)
+	})
+	joined := strings.Join(got, ",")
+	if !strings.Contains(joined, "DEEP-RULES") || !strings.Contains(joined, "SUB-RULES") {
+		t.Fatalf("nested instructions not discovered: %v", got)
+	}
+	if strings.Contains(joined, "ROOT-RULES") {
+		t.Fatalf("root AGENTS.md must be skipped: %v", got)
+	}
+	if len(got) != 2 || got[0] != "DEEP-RULES" || got[1] != "SUB-RULES" {
+		t.Fatalf("order = %v, want nearest first", got)
+	}
+
+	// 目录目标：目录自己的 AGENTS.md 也要发现。
+	got = nil
+	discoverInstructions(filepath.Join(root, "sub"), true, root, func(_ string, text string) {
+		got = append(got, text)
+	})
+	if len(got) != 1 || got[0] != "SUB-RULES" {
+		t.Fatalf("directory discovery = %v", got)
+	}
+
+	// 工作区外：不发现。
+	outside := t.TempDir()
+	writeTree(t, outside, map[string]string{"AGENTS.md": "OUTSIDE"})
+	got = nil
+	discoverInstructions(filepath.Join(outside, "x.go"), false, root, func(_ string, text string) {
+		got = append(got, text)
+	})
+	if len(got) != 0 {
+		t.Fatalf("outside instructions leaked: %v", got)
+	}
+}
+
+// TestReadFeedsNestedInstructions：读取子目录文件时，read 把发现的约定交给宿主钩子。
+func TestReadFeedsNestedInstructions(t *testing.T) {
+	root := t.TempDir()
+	writeTree(t, root, map[string]string{
+		"AGENTS.md":     "ROOT-RULES",
+		"sub/AGENTS.md": "SUB-RULES",
+		"sub/x.txt":     "hello",
+	})
+	var got []string
+	reg := NewRegistry()
+	for _, tl := range BuiltinWithHooks(root, NewFence(), nil, BuiltinHooks{
+		OnInstructions: func(path, text string) { got = append(got, text) },
+	}) {
+		if err := reg.Register(tl); err != nil {
+			t.Fatal(err)
+		}
+	}
+	r, _ := reg.Get("read")
+	if _, err := r.Run(context.Background(), `{"path":"sub/x.txt"}`); err != nil {
+		t.Fatal(err)
+	}
+	if len(got) != 1 || got[0] != "SUB-RULES" {
+		t.Fatalf("read hooks = %v", got)
+	}
+
+	// 根目录的文件不重复注入根约定。
+	got = nil
+	if _, err := r.Run(context.Background(), `{"path":"AGENTS.md"}`); err != nil {
+		t.Fatal(err)
+	}
+	if len(got) != 0 {
+		t.Fatalf("root instructions should not be discovered again: %v", got)
+	}
+}