Wire EXT-1 into downstream example; bump backend/documents gitlinks

Why: EXT-1 基座侧已落子仓（backend：处理器+owner 作用域句柄最小集；documents：申请卡提案），
下游示例随公开面更新示范 rdm.ping，Dev 记录两子仓指针。
Evidence: examples/downstream-rdm 注册 rdm.ping 处理器（读工件元数据+写审计）并补 fake registry/host 测试；
go.mod 按 compat-policy §4 追加 agent-system-core require+replace；cd examples/downstream-rdm && go test ./... 通过。
Impact: 仅示例与 gitlink；基座行为见 backend 提交。
Refs: modules/documents a47754b；modules/backend（feature/ext-1-inproc-handler）；任务卡 .task/feature-ext-1-inproc-handler.md。

examples/downstream-rdm/go.mod

@@ -2,6 +2,14 @@ module example.com/agent-system-plugin-rdm
 
 go 1.27
 
-require agent-system-backend v0.0.0
+require (
+	agent-system-backend v0.0.0
+	agent-system-core v0.0.0
+)
 
+// 声明式路径（仅 pkg/extension 根包）只需下面两条 replace。
+// 空白导入 pkg/extension/link 拉起完整后端时，须复制基座 go.mod 的
+// 全部 8 条 deps replace——见 README 与 extension-compat-policy §4。
 replace agent-system-backend => ../../modules/backend
+
+replace agent-system-core => ../../modules/backend/deps/agent-system-core

examples/downstream-rdm/plugin.go

@@ -1,12 +1,50 @@
 package rdm
 
-import "agent-system-backend/pkg/extension"
+import (
+	"context"
+	"encoding/json"
+
+	"agent-system-backend/pkg/extension"
+)
 
 func init() {
 	extension.RegisterCompiled(extension.InProc{
-		ID: "rdm",
-		Register: func(reg extension.Registry) error {
-			return reg.AddSkill("rdm-note", "# 研发记忆\n\n下游切片技能，不修改基座。\n")
-		},
+		ID:       "rdm",
+		Register: register,
 	})
 }
+
+// register 登记下游扩展：技能 + 进程内命令处理器（EXT-1 最小集示范）。
+func register(reg extension.Registry) error {
+	if err := reg.AddSkill("rdm-note", "# 研发记忆\n\n下游切片技能，不修改基座。\n"); err != nil {
+		return err
+	}
+	return reg.AddCommandHandler(json.RawMessage(`{
+		"id": "rdm.ping",
+		"title": "连通性自检",
+		"description": "读工件元数据 + 写审计，验证 EXT-1 owner 作用域宿主句柄",
+		"paramsSchema": {"type": "object", "properties": {"artifactId": {"type": "string"}}}
+	}`), rdmPing)
+}
+
+// rdmPing 经 owner 作用域宿主句柄：可选读工件元数据 → 写审计 → 返回回执。
+// 处理器自身不持有任何 owner 凭证，一切能力经 h 取用。
+func rdmPing(ctx context.Context, h extension.Host, req extension.Request) (any, error) {
+	artifact := ""
+	if id, _ := req.Params["artifactId"].(string); id != "" {
+		a, err := h.ArtifactGet(id)
+		if err != nil {
+			return nil, err
+		}
+		artifact = a.Name
+	}
+	if err := h.Audit("rdm.ping", req.ID, "{}"); err != nil {
+		return nil, err
+	}
+	return map[string]any{
+		"pong":     true,
+		"owner":    h.Owner(),
+		"plugin":   h.PluginID(),
+		"artifact": artifact,
+	}, nil
+}

examples/downstream-rdm/plugin_test.go

@@ -1,9 +1,13 @@
 package rdm
 
 import (
+	"context"
+	"encoding/json"
+	"errors"
 	"testing"
 
 	"agent-system-backend/pkg/extension"
+	core "agent-system-core"
 )
 
 func TestCompiledSkillRegistration(t *testing.T) {
@@ -17,3 +21,83 @@ func TestCompiledSkillRegistration(t *testing.T) {
 		t.Fatal("surface version required")
 	}
 }
+
+// fakeRegistry 记录 register() 的登记动作，不拉起基座。
+type fakeRegistry struct {
+	skills   []string
+	commands []string
+	handlers int
+}
+
+func (f *fakeRegistry) AddSkill(name, markdown string) error {
+	f.skills = append(f.skills, name)
+	return nil
+}
+func (f *fakeRegistry) AddCommand(spec json.RawMessage) error { return nil }
+func (f *fakeRegistry) AddCommandHandler(spec json.RawMessage, h extension.Handler) error {
+	var s struct {
+		ID string `json:"id"`
+	}
+	if err := json.Unmarshal(spec, &s); err != nil {
+		return err
+	}
+	if h == nil {
+		return errors.New("nil handler")
+	}
+	f.commands = append(f.commands, s.ID)
+	f.handlers++
+	return nil
+}
+func (f *fakeRegistry) Note(kind, name string, payload json.RawMessage) error { return nil }
+
+func TestRegisterBindsPingHandler(t *testing.T) {
+	reg := &fakeRegistry{}
+	if err := register(reg); err != nil {
+		t.Fatal(err)
+	}
+	if len(reg.skills) != 1 || reg.skills[0] != "rdm-note" {
+		t.Fatalf("skills: %+v", reg.skills)
+	}
+	if len(reg.commands) != 1 || reg.commands[0] != "rdm.ping" || reg.handlers != 1 {
+		t.Fatalf("commands: %+v handlers=%d", reg.commands, reg.handlers)
+	}
+}
+
+// fakeHost 是下游测试里的最小句柄替身：只实现 rdm.ping 用到的能力。
+type fakeHost struct{ owner string }
+
+func (f fakeHost) PluginID() string { return "rdm" }
+func (f fakeHost) Owner() string    { return f.owner }
+func (f fakeHost) KVPut(key, value string) error { return nil }
+func (f fakeHost) KVGet(key string) (string, bool, error) { return "", false, nil }
+func (f fakeHost) Audit(action, target, evidence string) error { return nil }
+func (f fakeHost) Complete(ctx context.Context, prompt string) (string, error) {
+	return "", nil
+}
+func (f fakeHost) KnowledgeSearch(ctx context.Context, projectID core.ID, text string, topK int) ([]core.RetrievalHit, error) {
+	return nil, nil
+}
+func (f fakeHost) KnowledgeWrite(ctx context.Context, docs []core.KnowledgeDoc, embed bool) error {
+	return nil
+}
+func (f fakeHost) TaskCreate(kind, title, conversationID string) (string, error) {
+	return "task_1", nil
+}
+func (f fakeHost) TaskUpdate(taskID, status string, progress int, errText string) error { return nil }
+func (f fakeHost) ArtifactGet(artifactID string) (core.Artifact, error) {
+	return core.Artifact{}, errors.New("not found")
+}
+func (f fakeHost) ArtifactContent(artifactID string) ([]byte, error) { return nil, nil }
+
+func TestRdmPingHandler(t *testing.T) {
+	out, err := rdmPing(context.Background(), fakeHost{owner: "alice"}, extension.Request{
+		ID: "rdm.ping", Owner: "alice", Params: map[string]any{},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	m, _ := out.(map[string]any)
+	if m["pong"] != true || m["owner"] != "alice" || m["plugin"] != "rdm" {
+		t.Fatalf("payload: %+v", out)
+	}
+}