diff --git a/adapters/a2a/card.go b/adapters/a2a/card.go
new file mode 100644
index 0000000..d4c9b97
--- /dev/null
+++ b/adapters/a2a/card.go
@@ -0,0 +1,179 @@
+// Package a2a 把小队接入 A2A（Agent2Agent）1.0 互通面（Q3 WP4）：
+//   - 发布侧：BuildCard 从角色注册表与蓝图注册表渲染 Agent Card（描述本
+//     团队能力），CardHandler 以 JSON 服务（挂载在
+//     /.well-known/agent-card.json）；
+//   - 消费侧：FetchCard 发现远端 Agent Card（fail-closed 校验必备字段），
+//     Executor 实现 squad.Executor——message/send 发起任务，tasks/get 轮询
+//     A2A 任务状态机（submitted/working/input-required → completed/failed/
+//     canceled），终态映射 ExecResult：completed 的 artifacts（TextPart/
+//     FilePart）落成 patches/目标文件；failed/canceled/input-required 一律
+//     Success=false（跨进程挂起不在本适配面内，fail-closed 交引擎重试/降级
+//     语义处理）。
+//
+// 传输为 JSON-RPC 2.0 over HTTP（A2A 1.0 形态）；不引入协议之外的依赖。
+package a2a
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strings"
+
+	"agent-squad/squad"
+)
+
+// ProtocolVersion 对齐的 A2A 协议版本。
+const ProtocolVersion = "1.0"
+
+// WellKnownPath 是 Agent Card 的发现路径（A2A 1.0）。
+const WellKnownPath = "/.well-known/agent-card.json"
+
+// AgentCard 是 A2A 1.0 Agent Card（发布与消费共用形态）。
+type AgentCard struct {
+	ProtocolVersion string `json:"protocolVersion"`
+	Name            string `json:"name"`
+	Description     string `json:"description,omitempty"`
+	// URL 是 JSON-RPC 服务端点（消费侧据此发 message/send）。
+	URL         string   `json:"url"`
+	Version     string   `json:"version"`
+	Capabilities CardCapabilities `json:"capabilities"`
+	DefaultInputModes  []string `json:"defaultInputModes,omitempty"`
+	DefaultOutputModes []string `json:"defaultOutputModes,omitempty"`
+	Skills      []AgentSkill `json:"skills,omitempty"`
+}
+
+// CardCapabilities 能力声明（本适配面：非流式、无推送、无状态历史）。
+type CardCapabilities struct {
+	Streaming              bool `json:"streaming"`
+	PushNotifications      bool `json:"pushNotifications"`
+	StateTransitionHistory bool `json:"stateTransitionHistory"`
+}
+
+// AgentSkill 是一项可被远端调用的能力。
+type AgentSkill struct {
+	ID          string   `json:"id"`
+	Name        string   `json:"name"`
+	Description string   `json:"description,omitempty"`
+	Tags        []string `json:"tags,omitempty"`
+	Examples    []string `json:"examples,omitempty"`
+}
+
+// CardOptions 覆盖 BuildCard 的身份字段（空则用缺省）。
+type CardOptions struct {
+	Name        string
+	Description string
+	// URL JSON-RPC 端点（必填：远端没有端点就无法调用本团队）。
+	URL string
+	// Version 卡片版本（空 = "1.0.0"）。
+	Version string
+	// Skills 显式能力清单；空 = 从注册表派生。
+	Skills []AgentSkill
+}
+
+// BuildCard 从角色注册表与蓝图注册表渲染 Agent Card（描述本团队能力）。
+// 角色 → 技能（关键词作 tags）；蓝图 → 技能（match 词作 examples）。
+func BuildCard(reg *squad.RoleRegistry, bps *squad.BlueprintRegistry, opts CardOptions) (AgentCard, error) {
+	if strings.TrimSpace(opts.URL) == "" {
+		return AgentCard{}, fmt.Errorf("a2a: Agent Card 需要 JSON-RPC 端点 URL")
+	}
+	card := AgentCard{
+		ProtocolVersion: ProtocolVersion,
+		Name:            orDefault(opts.Name, "agent-squad"),
+		Description:     opts.Description,
+		URL:             opts.URL,
+		Version:         orDefault(opts.Version, "1.0.0"),
+		DefaultInputModes:  []string{"text/plain"},
+		DefaultOutputModes: []string{"text/plain"},
+		Skills:          append([]AgentSkill(nil), opts.Skills...),
+	}
+	if len(card.Skills) == 0 {
+		if reg != nil {
+			for _, role := range reg.List() {
+				desc := firstLine(role.Instructions)
+				if desc == "" {
+					desc = role.Name
+				}
+				card.Skills = append(card.Skills, AgentSkill{
+					ID: role.Role, Name: orDefault(role.Name, role.Role),
+					Description: desc, Tags: append([]string(nil), role.Keywords...),
+				})
+			}
+		}
+		if bps != nil {
+			for _, bp := range bps.List() {
+				card.Skills = append(card.Skills, AgentSkill{
+					ID: bp.Key, Name: orDefault(bp.Title, bp.Key),
+					Description: bp.Description, Examples: append([]string(nil), bp.Match...),
+				})
+			}
+		}
+	}
+	return card, nil
+}
+
+// CardHandler 以 JSON 服务 Agent Card（调用方挂载到 WellKnownPath）。
+func CardHandler(card AgentCard) http.Handler {
+	body, _ := json.Marshal(card)
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write(body)
+	})
+}
+
+// FetchCard 发现并校验远端 Agent Card（fail-closed：必备字段缺失即拒）。
+func FetchCard(client *http.Client, wellKnownURL string) (AgentCard, error) {
+	if client == nil {
+		client = http.DefaultClient
+	}
+	resp, err := client.Get(wellKnownURL)
+	if err != nil {
+		return AgentCard{}, fmt.Errorf("a2a: 获取 Agent Card: %w", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return AgentCard{}, fmt.Errorf("a2a: Agent Card 端点返回 %d", resp.StatusCode)
+	}
+	var card AgentCard
+	if err := json.NewDecoder(resp.Body).Decode(&card); err != nil {
+		return AgentCard{}, fmt.Errorf("a2a: Agent Card 解析失败: %w", err)
+	}
+	if err := validateCard(card); err != nil {
+		return AgentCard{}, err
+	}
+	return card, nil
+}
+
+// validateCard 消费侧最小校验（A2A 1.0 必备字段）。
+func validateCard(card AgentCard) error {
+	if card.ProtocolVersion == "" {
+		return fmt.Errorf("a2a: Agent Card 缺 protocolVersion")
+	}
+	if strings.TrimSpace(card.Name) == "" {
+		return fmt.Errorf("a2a: Agent Card 缺 name")
+	}
+	if strings.TrimSpace(card.URL) == "" {
+		return fmt.Errorf("a2a: Agent Card 缺 url")
+	}
+	if strings.TrimSpace(card.Version) == "" {
+		return fmt.Errorf("a2a: Agent Card 缺 version")
+	}
+	return nil
+}
+
+func orDefault(v, def string) string {
+	if strings.TrimSpace(v) != "" {
+		return v
+	}
+	return def
+}
+
+func firstLine(s string) string {
+	s = strings.TrimSpace(s)
+	if i := strings.IndexByte(s, '\n'); i >= 0 {
+		s = s[:i]
+	}
+	if len(s) > 120 {
+		s = s[:120] + "…"
+	}
+	return s
+}
diff --git a/adapters/a2a/conformance_test.go b/adapters/a2a/conformance_test.go
new file mode 100644
index 0000000..b9bf1e0
--- /dev/null
+++ b/adapters/a2a/conformance_test.go
@@ -0,0 +1,345 @@
+package a2a
+
+import (
+	"context"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"agent-squad/squad"
+)
+
+// conformance_test.go — Q3 WP4 验收：双向 conformance（本地假 A2A 服务端）。
+// 发布侧：BuildCard + CardHandler 在 well-known 路径服务合法 Agent Card；
+// 消费侧：FetchCard 发现校验 + Executor 走完任务状态机
+// （submitted→working→completed / failed / input-required），终态对齐
+// squad.ExecResult。
+
+// fakeA2AServer 最小 A2A 1.0 服务端：well-known 卡片 + JSON-RPC
+// （message/send 建任务；tasks/get 按脚本推进状态）。
+type fakeA2AServer struct {
+	mu     sync.Mutex
+	card   AgentCard
+	tasks  map[string]*Task
+	plan   []string // 每次 tasks/get 推进到的状态序列（走完停在末态）
+	calls  map[string]int
+	artifacts []Artifact
+	statusMsg string
+}
+
+func newFakeServer(t *testing.T, card AgentCard, plan []string, artifacts []Artifact) *fakeA2AServer {
+	t.Helper()
+	s := &fakeA2AServer{card: card, tasks: map[string]*Task{}, plan: plan,
+		calls: map[string]int{}, artifacts: artifacts}
+	return s
+}
+
+func (s *fakeA2AServer) handler() http.Handler {
+	mux := http.NewServeMux()
+	mux.HandleFunc(WellKnownPath, func(w http.ResponseWriter, r *http.Request) {
+		s.mu.Lock()
+		body, _ := json.Marshal(s.card)
+		s.mu.Unlock()
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write(body)
+	})
+	mux.HandleFunc("/rpc", func(w http.ResponseWriter, r *http.Request) {
+		var req rpcRequest
+		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+			writeRPCError(w, 0, -32700, "parse error")
+			return
+		}
+		s.mu.Lock()
+		defer s.mu.Unlock()
+		s.calls[req.Method]++
+		switch req.Method {
+		case "message/send":
+			id := fmt.Sprintf("task_%d", len(s.tasks)+1)
+			state := StateSubmitted
+			if len(s.plan) > 0 {
+				state = s.plan[0]
+			}
+			task := &Task{Kind: "task", ID: id, ContextID: "ctx_1",
+				Status: TaskStatus{State: state, Message: s.statusMessage()}}
+			s.tasks[id] = task
+			writeRPCResult(w, req.ID, task)
+		case "tasks/get":
+			var params struct {
+				ID string `json:"id"`
+			}
+			raw, _ := json.Marshal(req.Params)
+			_ = json.Unmarshal(raw, &params)
+			task, ok := s.tasks[params.ID]
+			if !ok {
+				writeRPCError(w, req.ID, -32001, "task not found")
+				return
+			}
+			// 按脚本推进状态机（停留在终态）。
+			if !isTerminal(task.Status.State) && len(s.plan) > 0 {
+				n := s.calls["tasks/get#"+params.ID]
+				s.calls["tasks/get#"+params.ID] = n + 1
+				idx := n + 1
+				if idx >= len(s.plan) {
+					idx = len(s.plan) - 1
+				}
+				task.Status.State = s.plan[idx]
+				task.Status.Message = s.statusMessage()
+				if task.Status.State == StateCompleted {
+					task.Artifacts = s.artifacts
+				}
+			}
+			writeRPCResult(w, req.ID, task)
+		default:
+			writeRPCError(w, req.ID, -32601, "method not found")
+		}
+	})
+	return mux
+}
+
+func (s *fakeA2AServer) statusMessage() *Message {
+	if s.statusMsg == "" {
+		return nil
+	}
+	return &Message{Kind: "message", Role: "agent",
+		Parts: []Part{{Kind: "text", Text: s.statusMsg}}}
+}
+
+func writeRPCResult(w http.ResponseWriter, id int64, result any) {
+	body, _ := json.Marshal(result)
+	env, _ := json.Marshal(rpcResponse{JSONRPC: "2.0", ID: id, Result: body})
+	w.Header().Set("Content-Type", "application/json")
+	_, _ = w.Write(env)
+}
+
+func writeRPCError(w http.ResponseWriter, id int64, code int, msg string) {
+	env, _ := json.Marshal(rpcResponse{JSONRPC: "2.0", ID: id, Error: &rpcError{Code: code, Message: msg}})
+	w.Header().Set("Content-Type", "application/json")
+	_, _ = w.Write(env)
+}
+
+// ---- 发布侧 ----
+
+func TestBuildCardFromRegistries(t *testing.T) {
+	reg := squad.NewRoleRegistry()
+	for _, r := range []squad.RoleSpec{
+		{Role: "researcher", Name: "调研员", Keywords: []string{"调研", "检索"},
+			Instructions: "围绕目标调研关键问题。\n第二行不进摘要。"},
+		{Role: "writer", Name: "撰稿员", Keywords: []string{"撰写"}},
+	} {
+		if err := reg.Register(r); err != nil {
+			t.Fatal(err)
+		}
+	}
+	bps := squad.NewBlueprintRegistry()
+	if err := bps.Register(squad.Blueprint{Key: "brief", Title: "简报",
+		Description: "生成简报", Match: []string{"简报", "brief"},
+		Steps: []squad.StepSpec{{ID: "s1", Role: "writer", Title: "成文"}}}); err != nil {
+		t.Fatal(err)
+	}
+	card, err := BuildCard(reg, bps, CardOptions{
+		Name: "示例小队", Description: "演示团队能力", URL: "https://team.example/rpc",
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if card.ProtocolVersion != ProtocolVersion || card.Version != "1.0.0" {
+		t.Fatalf("card = %+v", card)
+	}
+	byID := map[string]AgentSkill{}
+	for _, s := range card.Skills {
+		byID[s.ID] = s
+	}
+	if byID["researcher"].Name != "调研员" || byID["researcher"].Description != "围绕目标调研关键问题。" {
+		t.Fatalf("role skill = %+v", byID["researcher"])
+	}
+	if len(byID["researcher"].Tags) != 2 {
+		t.Fatalf("tags = %v", byID["researcher"].Tags)
+	}
+	if byID["brief"].Name != "简报" || strings.Join(byID["brief"].Examples, ",") != "简报,brief" {
+		t.Fatalf("blueprint skill = %+v", byID["brief"])
+	}
+	if _, err := BuildCard(reg, bps, CardOptions{}); err == nil {
+		t.Fatal("缺 URL 必须 fail-closed")
+	}
+}
+
+// CardHandler 以 JSON 服务卡片（发布端点形态）。
+func TestCardHandlerServesJSON(t *testing.T) {
+	card := AgentCard{ProtocolVersion: ProtocolVersion, Name: "小队", URL: "https://x/rpc", Version: "1.0.0"}
+	ts := httptest.NewServer(CardHandler(card))
+	defer ts.Close()
+	resp, err := http.Get(ts.URL + WellKnownPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if ct := resp.Header.Get("Content-Type"); ct != "application/json" {
+		t.Fatalf("content-type = %s", ct)
+	}
+	var got AgentCard
+	if err := json.NewDecoder(resp.Body).Decode(&got); err != nil {
+		t.Fatal(err)
+	}
+	if got.Name != "小队" || got.ProtocolVersion != ProtocolVersion {
+		t.Fatalf("card = %+v", got)
+	}
+}
+
+// ---- 消费侧：发现 + 状态机 ----
+
+func TestFetchCardAndExecuteCompleted(t *testing.T) {
+	fileBytes := base64.StdEncoding.EncodeToString([]byte("notes 内容"))
+	artifacts := []Artifact{{
+		ArtifactID: "art1", Name: "调研结果",
+		Parts: []Part{
+			{Kind: "text", Text: "# 调研结论\n\n结论正文，长度足够作为交付物内容。"},
+			{Kind: "file", File: &FilePart{Name: "notes.md", Bytes: fileBytes, MimeType: "text/markdown"}},
+		},
+	}}
+	card := AgentCard{ProtocolVersion: ProtocolVersion, Name: "远端小队",
+		URL: "PLACEHOLDER", Version: "1.0.0"}
+	srv := newFakeServer(t, card, []string{StateWorking, StateWorking, StateCompleted}, artifacts)
+	ts := httptest.NewServer(srv.handler())
+	defer ts.Close()
+	srv.mu.Lock()
+	srv.card.URL = ts.URL + "/rpc"
+	srv.mu.Unlock()
+
+	// 发现：well-known 路径取卡并校验。
+	got, err := FetchCard(ts.Client(), ts.URL+WellKnownPath)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.Name != "远端小队" || got.URL != ts.URL+"/rpc" {
+		t.Fatalf("card = %+v", got)
+	}
+
+	// 执行：submitted/working → completed，工件映射 patches。
+	var states []string
+	ex := NewExecutor(got)
+	ex.Client = ts.Client()
+	ex.PollInterval = 5 * time.Millisecond
+	ex.OnState = func(s string) { states = append(states, s) }
+	res, err := ex.Execute(context.Background(), squad.ExecRequest{
+		Prompt: "调研主题 X", Targets: []string{"output.md"},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !res.Success {
+		t.Fatalf("result = %+v", res)
+	}
+	if string(res.Patches["notes.md"]) != "notes 内容" {
+		t.Fatalf("file part 未落成 patch：%q", res.Patches["notes.md"])
+	}
+	if !strings.Contains(string(res.Patches["output.md"]), "调研结论") {
+		t.Fatalf("文本部件未写入目标：%q", res.Patches["output.md"])
+	}
+	joined := strings.Join(states, ",")
+	if !strings.Contains(joined, StateWorking) || !strings.HasSuffix(joined, StateCompleted) {
+		t.Fatalf("状态机迁移 = %v", states)
+	}
+	srv.mu.Lock()
+	sends := srv.calls["message/send"]
+	srv.mu.Unlock()
+	if sends != 1 {
+		t.Fatalf("message/send = %d", sends)
+	}
+}
+
+func TestExecuteMapsFailedAndInputRequired(t *testing.T) {
+	card := AgentCard{ProtocolVersion: ProtocolVersion, Name: "远端", URL: "PLACEHOLDER", Version: "1"}
+	srv := newFakeServer(t, card, []string{StateWorking, StateFailed}, nil)
+	srv.statusMsg = "远端执行崩溃"
+	ts := httptest.NewServer(srv.handler())
+	defer ts.Close()
+	srv.mu.Lock()
+	srv.card.URL = ts.URL + "/rpc"
+	srv.mu.Unlock()
+
+	ex := NewExecutor(card)
+	ex.BaseURL = ts.URL + "/rpc"
+	ex.Client = ts.Client()
+	ex.PollInterval = 5 * time.Millisecond
+	res, err := ex.Execute(context.Background(), squad.ExecRequest{Prompt: "x", Targets: []string{"output.md"}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if res.Success || !strings.Contains(res.ErrorReason, "failed") || !strings.Contains(res.ErrorReason, "远端执行崩溃") {
+		t.Fatalf("failed 映射 = %+v", res)
+	}
+
+	// input-required：fail-closed（跨进程人工输入不在适配面内）。
+	srv2 := newFakeServer(t, card, []string{StateInputRequired}, nil)
+	srv2.statusMsg = "请补充授权"
+	ts2 := httptest.NewServer(srv2.handler())
+	defer ts2.Close()
+	ex2 := &Executor{BaseURL: ts2.URL + "/rpc", Client: ts2.Client(), PollInterval: 5 * time.Millisecond}
+	res2, err := ex2.Execute(context.Background(), squad.ExecRequest{Prompt: "x", Targets: []string{"output.md"}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if res2.Success || !strings.Contains(res2.ErrorReason, "input-required") {
+		t.Fatalf("input-required 映射 = %+v", res2)
+	}
+}
+
+// 直接回 Message（无任务态）→ 文本落目标。
+func TestExecuteDirectMessageResult(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var req rpcRequest
+		_ = json.NewDecoder(r.Body).Decode(&req)
+		writeRPCResult(w, req.ID, Message{Kind: "message", Role: "agent",
+			Parts: []Part{{Kind: "text", Text: "直接回答正文"}}})
+	}))
+	defer ts.Close()
+	ex := &Executor{BaseURL: ts.URL, Client: ts.Client()}
+	res, err := ex.Execute(context.Background(), squad.ExecRequest{Prompt: "x", Targets: []string{"output.md"}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !res.Success || !strings.Contains(string(res.Patches["output.md"]), "直接回答正文") {
+		t.Fatalf("res = %+v", res)
+	}
+}
+
+// 传输/协议错误 → error（引擎按瞬态评估），不吞成成功。
+func TestExecuteProtocolErrors(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		writeRPCError(w, 1, -32601, "method not found")
+	}))
+	defer ts.Close()
+	ex := &Executor{BaseURL: ts.URL, Client: ts.Client()}
+	if _, err := ex.Execute(context.Background(), squad.ExecRequest{Prompt: "x"}); err == nil ||
+		!strings.Contains(err.Error(), "协议错误") {
+		t.Fatalf("err = %v", err)
+	}
+	// ctx 取消传播。
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+	slow := newFakeServer(t, AgentCard{ProtocolVersion: "1.0", Name: "x", URL: ts.URL, Version: "1"},
+		[]string{StateWorking}, nil)
+	ts2 := httptest.NewServer(slow.handler())
+	defer ts2.Close()
+	ex2 := &Executor{BaseURL: ts2.URL + "/rpc", Client: ts2.Client(), PollInterval: time.Second}
+	if _, err := ex2.Execute(ctx, squad.ExecRequest{Prompt: "x"}); err == nil {
+		t.Fatal("取消必须传播")
+	}
+}
+
+// FetchCard fail-closed：缺必备字段拒绝。
+func TestFetchCardValidates(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, _ = w.Write([]byte(`{"protocolVersion":"1.0","name":"","url":"","version":""}`))
+	}))
+	defer ts.Close()
+	if _, err := FetchCard(ts.Client(), ts.URL); err == nil || !strings.Contains(err.Error(), "name") {
+		t.Fatalf("err = %v", err)
+	}
+}
diff --git a/adapters/a2a/executor.go b/adapters/a2a/executor.go
new file mode 100644
index 0000000..6c016cb
--- /dev/null
+++ b/adapters/a2a/executor.go
@@ -0,0 +1,331 @@
+package a2a
+
+import (
+	"bytes"
+	"context"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+	"sync/atomic"
+	"time"
+
+	"agent-squad/squad"
+)
+
+// executor.go — 远端智能体 Executor 客户端（A2A 任务状态机对齐 ExecResult）。
+
+// 任务状态（A2A 1.0 TaskState）。
+const (
+	StateSubmitted    = "submitted"
+	StateWorking      = "working"
+	StateInputRequired = "input-required"
+	StateCompleted    = "completed"
+	StateCanceled     = "canceled"
+	StateFailed       = "failed"
+	StateRejected     = "rejected"
+)
+
+// DefaultPollInterval 是 tasks/get 轮询缺省间隔。
+const DefaultPollInterval = 500 * time.Millisecond
+
+// Executor 把远端 A2A 智能体接成 squad.Executor：一次步骤执行 = 一个
+// A2A 任务（message/send 发起，tasks/get 轮询到终态）。
+type Executor struct {
+	// BaseURL 远端 JSON-RPC 端点（Agent Card 的 url）。
+	BaseURL string
+	// Client HTTP 客户端（nil = http.DefaultClient）。
+	Client *http.Client
+	// PollInterval 轮询间隔（0 = DefaultPollInterval）。
+	PollInterval time.Duration
+	// OnState 可选状态回调（观测任务状态机迁移）。
+	OnState func(state string)
+
+	callID atomic.Int64
+}
+
+// NewExecutor 按 Agent Card 构造远端执行器。
+func NewExecutor(card AgentCard) *Executor {
+	return &Executor{BaseURL: card.URL}
+}
+
+// Name 实现 squad.Executor。
+func (e *Executor) Name() string { return "a2a" }
+
+// ---- A2A 1.0 报文形态（JSON-RPC 2.0） ----
+
+type rpcRequest struct {
+	JSONRPC string `json:"jsonrpc"`
+	ID      int64  `json:"id"`
+	Method  string `json:"method"`
+	Params  any    `json:"params"`
+}
+
+type rpcError struct {
+	Code    int    `json:"code"`
+	Message string `json:"message"`
+}
+
+type rpcResponse struct {
+	JSONRPC string          `json:"jsonrpc"`
+	ID      int64           `json:"id"`
+	Result  json.RawMessage `json:"result,omitempty"`
+	Error   *rpcError       `json:"error,omitempty"`
+}
+
+// Part 是消息/工件的部件（text | file | data）。
+type Part struct {
+	Kind string     `json:"kind"`
+	Text string     `json:"text,omitempty"`
+	File *FilePart  `json:"file,omitempty"`
+	Data *json.RawMessage `json:"data,omitempty"`
+}
+
+// FilePart 文件部件：bytes（base64）或 uri 二选一。
+type FilePart struct {
+	Name     string `json:"name"`
+	Bytes    string `json:"bytes,omitempty"`
+	URI      string `json:"uri,omitempty"`
+	MimeType string `json:"mimeType,omitempty"`
+}
+
+// Message 是一条 A2A 消息。
+type Message struct {
+	Kind      string `json:"kind"`
+	Role      string `json:"role"`
+	Parts     []Part `json:"parts"`
+	MessageID string `json:"messageId"`
+}
+
+// TaskStatus 任务状态。
+type TaskStatus struct {
+	State    string   `json:"state"`
+	Message  *Message `json:"message,omitempty"`
+	Timestamp string  `json:"timestamp,omitempty"`
+}
+
+// Artifact 任务工件。
+type Artifact struct {
+	ArtifactID string `json:"artifactId,omitempty"`
+	Name       string `json:"name,omitempty"`
+	Parts      []Part `json:"parts"`
+}
+
+// Task 是 A2A 任务（状态机载体）。
+type Task struct {
+	Kind      string     `json:"kind"`
+	ID        string     `json:"id"`
+	ContextID string     `json:"contextId,omitempty"`
+	Status    TaskStatus `json:"status"`
+	Artifacts []Artifact `json:"artifacts,omitempty"`
+}
+
+// Execute 实现 squad.Executor：发起任务并轮询到终态，映射 ExecResult。
+// 传输/协议错误返回 error（引擎按瞬态失败评估）；任务级失败
+// （failed/canceled/rejected/input-required）返回 Success=false 的结果
+// （fail-closed：跨进程人工输入不在本适配面内）。
+func (e *Executor) Execute(ctx context.Context, req squad.ExecRequest) (*squad.ExecResult, error) {
+	if strings.TrimSpace(e.BaseURL) == "" {
+		return nil, fmt.Errorf("a2a: executor 缺 BaseURL")
+	}
+	prompt := strings.TrimSpace(req.Prompt)
+	if prompt == "" {
+		prompt = strings.TrimSpace(req.Instructions)
+	}
+	msg := Message{
+		Kind: "message", Role: "user",
+		Parts:     []Part{{Kind: "text", Text: prompt}},
+		MessageID: fmt.Sprintf("msg-%d-%d", time.Now().UnixNano(), e.callID.Add(1)),
+	}
+	raw, err := e.call(ctx, "message/send", map[string]any{"message": msg})
+	if err != nil {
+		return nil, err
+	}
+	// 服务端可直接回 Message（无任务态）或 Task。
+	var probe struct {
+		Kind string `json:"kind"`
+	}
+	_ = json.Unmarshal(raw, &probe)
+	if probe.Kind == "message" {
+		var m Message
+		if err := json.Unmarshal(raw, &m); err != nil {
+			return nil, fmt.Errorf("a2a: message 结果解析失败: %w", err)
+		}
+		return e.resultFromParts(m.Parts, req.Targets), nil
+	}
+	var task Task
+	if err := json.Unmarshal(raw, &task); err != nil {
+		return nil, fmt.Errorf("a2a: task 结果解析失败: %w", err)
+	}
+	e.observe(task.Status.State)
+	if shouldStop(task.Status.State) {
+		return e.resultFromTask(task, req.Targets), nil
+	}
+	// 轮询任务状态机直至终态（ctx 取消传播）。
+	interval := e.PollInterval
+	if interval <= 0 {
+		interval = DefaultPollInterval
+	}
+	ticker := time.NewTicker(interval)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		case <-ticker.C:
+		}
+		raw, err := e.call(ctx, "tasks/get", map[string]any{"id": task.ID})
+		if err != nil {
+			return nil, err
+		}
+		var next Task
+		if err := json.Unmarshal(raw, &next); err != nil {
+			return nil, fmt.Errorf("a2a: tasks/get 解析失败: %w", err)
+		}
+		if next.Status.State != task.Status.State {
+			task = next
+			e.observe(task.Status.State)
+		} else {
+			task = next
+		}
+		if shouldStop(task.Status.State) {
+			return e.resultFromTask(task, req.Targets), nil
+		}
+	}
+}
+
+// call 发一次 JSON-RPC 调用并取 result。
+func (e *Executor) call(ctx context.Context, method string, params any) (json.RawMessage, error) {
+	client := e.Client
+	if client == nil {
+		client = http.DefaultClient
+	}
+	body, _ := json.Marshal(rpcRequest{
+		JSONRPC: "2.0", ID: e.callID.Add(1), Method: method, Params: params,
+	})
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, e.BaseURL, bytes.NewReader(body))
+	if err != nil {
+		return nil, err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("a2a: %s 传输失败: %w", method, err)
+	}
+	defer resp.Body.Close()
+	data, err := io.ReadAll(io.LimitReader(resp.Body, 8<<20))
+	if err != nil {
+		return nil, fmt.Errorf("a2a: %s 读取响应失败: %w", method, err)
+	}
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("a2a: %s 返回 HTTP %d", method, resp.StatusCode)
+	}
+	var env rpcResponse
+	if err := json.Unmarshal(data, &env); err != nil {
+		return nil, fmt.Errorf("a2a: %s 响应不是合法 JSON-RPC: %w", method, err)
+	}
+	if env.Error != nil {
+		return nil, fmt.Errorf("a2a: %s 协议错误 %d: %s", method, env.Error.Code, env.Error.Message)
+	}
+	return env.Result, nil
+}
+
+func (e *Executor) observe(state string) {
+	if e.OnState != nil {
+		e.OnState(state)
+	}
+}
+
+func isTerminal(state string) bool {
+	switch state {
+	case StateCompleted, StateFailed, StateCanceled, StateRejected:
+		return true
+	}
+	return false
+}
+
+// shouldStop 轮询停止条件：真终态，或 input-required（跨进程人工输入不在
+// 本适配面内，fail-closed 交引擎语义处理，不死等）。
+func shouldStop(state string) bool {
+	return isTerminal(state) || state == StateInputRequired
+}
+
+// resultFromTask 终态任务 → ExecResult。
+func (e *Executor) resultFromTask(task Task, targets []string) *squad.ExecResult {
+	switch task.Status.State {
+	case StateCompleted:
+		var parts []Part
+		for _, art := range task.Artifacts {
+			parts = append(parts, art.Parts...)
+		}
+		return e.resultFromParts(parts, targets)
+	case StateInputRequired:
+		return &squad.ExecResult{Success: false,
+			ErrorReason: "a2a: 远端要求人工输入（input-required）：" + statusText(task.Status)}
+	case StateCanceled:
+		return &squad.ExecResult{Success: false,
+			ErrorReason: "a2a: 远端任务被取消（canceled）：" + statusText(task.Status)}
+	case StateRejected:
+		return &squad.ExecResult{Success: false,
+			ErrorReason: "a2a: 远端拒绝任务（rejected）：" + statusText(task.Status)}
+	default: // failed 及未知终态一律 fail-closed
+		return &squad.ExecResult{Success: false,
+			ErrorReason: "a2a: 远端任务失败（" + task.Status.State + "）：" + statusText(task.Status)}
+	}
+}
+
+// resultFromParts 部件流 → patches：FilePart(bytes) 按名落 patch；
+// 文本部件拼接后写入全部声明目标（无文件工件时的交付物兜底，
+// 与其他后端「正文写目标文件」契约一致）。
+func (e *Executor) resultFromParts(parts []Part, targets []string) *squad.ExecResult {
+	patches := map[string][]byte{}
+	var text strings.Builder
+	for _, p := range parts {
+		switch p.Kind {
+		case "text":
+			if text.Len() > 0 {
+				text.WriteString("\n")
+			}
+			text.WriteString(p.Text)
+		case "file":
+			if p.File == nil || p.File.Name == "" {
+				continue
+			}
+			data, err := base64.StdEncoding.DecodeString(p.File.Bytes)
+			if err != nil {
+				continue // uri 形态与坏 base64 不落 patch（消费侧最小面）
+			}
+			patches[p.File.Name] = data
+		}
+	}
+	body := strings.TrimSpace(text.String())
+	if len(targets) == 0 {
+		targets = []string{"output.md"}
+	}
+	if body != "" {
+		for _, t := range targets {
+			if _, ok := patches[t]; !ok {
+				patches[t] = []byte(body + "\n")
+			}
+		}
+	}
+	if len(patches) == 0 {
+		return &squad.ExecResult{Success: false, ErrorReason: "a2a: 完成任务无任何工件"}
+	}
+	return &squad.ExecResult{Success: true, Patches: patches, Logs: body}
+}
+
+func statusText(st TaskStatus) string {
+	if st.Message == nil {
+		return ""
+	}
+	var b strings.Builder
+	for _, p := range st.Message.Parts {
+		if p.Kind == "text" {
+			b.WriteString(p.Text)
+		}
+	}
+	return b.String()
+}
diff --git a/adapters/a2a/go.mod b/adapters/a2a/go.mod
new file mode 100644
index 0000000..141ea0b
--- /dev/null
+++ b/adapters/a2a/go.mod
@@ -0,0 +1,11 @@
+module agent-squad/adapters/a2a
+
+go 1.27
+
+require agent-squad v0.0.0
+
+require error-code-system v0.0.0 // indirect
+
+replace agent-squad => ../..
+
+replace error-code-system => ../../deps/error-code-system