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。

llm/image_test.go

@@ -0,0 +1,92 @@
+package llm
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// 1x1 红色 PNG
+const tinyPNG = "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNkYPhfDwAChwGA60e6kgAAAABJRU5ErkJggg=="
+
+func writeTinyPNG(t *testing.T) string {
+	t.Helper()
+	data, _ := base64.StdEncoding.DecodeString(tinyPNG)
+	path := filepath.Join(t.TempDir(), "shot.png")
+	if err := os.WriteFile(path, data, 0o644); err != nil {
+		t.Fatal(err)
+	}
+	return path
+}
+
+func TestLoadImage(t *testing.T) {
+	path := writeTinyPNG(t)
+	b64, mt, err := LoadImage(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if mt != "image/png" || b64 != tinyPNG {
+		t.Fatalf("roundtrip failed: mt=%s len=%d", mt, len(b64))
+	}
+	if _, _, err := LoadImage("x.txt"); err == nil {
+		t.Fatal("expected unsupported type error")
+	}
+}
+
+func TestOpenAISerializationWithImages(t *testing.T) {
+	path := writeTinyPNG(t)
+	msgs := []Message{
+		{Role: RoleUser, Content: "look", Images: []Image{{Path: path}}},
+		{Role: RoleTool, ToolCallID: "t1", Content: "done", Images: []Image{{Path: path}}},
+	}
+	out := oaBuildMessages("sys", msgs)
+	// user 消息 → content parts 数组（text + image_url）
+	u := out[1]
+	if u["role"] != "user" {
+		t.Fatalf("role: %v", u["role"])
+	}
+	parts, _ := json.Marshal(u["content"])
+	if !strings.Contains(string(parts), `"image_url"`) || !strings.Contains(string(parts), "data:image/png;base64,") {
+		t.Fatalf("user image parts: %s", parts)
+	}
+	// tool result → tool 消息 + 紧随的 user 附图消息
+	if out[2]["role"] != "tool" || out[3]["role"] != "user" {
+		t.Fatalf("tool+image layout wrong: %v %v", out[2]["role"], out[3]["role"])
+	}
+	parts, _ = json.Marshal(out[3]["content"])
+	if !strings.Contains(string(parts), "data:image/png") {
+		t.Fatalf("tool image parts: %s", parts)
+	}
+}
+
+func TestAnthropicSerializationWithImages(t *testing.T) {
+	path := writeTinyPNG(t)
+	msgs := []Message{
+		{Role: RoleTool, ToolCallID: "t1", Content: "shot", Images: []Image{{Path: path}}},
+		{Role: RoleUser, Content: "look again", Images: []Image{{Path: path}}},
+	}
+	out := anBuildMessages(msgs, false)
+	body, _ := json.Marshal(out)
+	if !strings.Contains(string(body), `"type":"tool_result"`) ||
+		!strings.Contains(string(body), `"type":"image"`) ||
+		!strings.Contains(string(body), `"media_type":"image/png"`) {
+		t.Fatalf("anthropic serialization: %s", body)
+	}
+}
+
+func TestImageUnavailableDegradation(t *testing.T) {
+	msgs := []Message{{Role: RoleUser, Content: "look", Images: []Image{{Path: "/nonexistent/shot.png"}}}}
+	oa := oaBuildMessages("s", msgs)
+	body, _ := json.Marshal(oa[1]["content"])
+	if !strings.Contains(string(body), "[image unavailable") {
+		t.Fatalf("openai degradation missing: %s", body)
+	}
+	an := anBuildMessages(msgs, false)
+	body, _ = json.Marshal(an[0]["content"])
+	if !strings.Contains(string(body), "[image unavailable") {
+		t.Fatalf("anthropic degradation missing: %s", body)
+	}
+}