diff --git a/internal/app/app.go b/internal/app/app.go
index 56615b9..9f3cf9d 100644
--- a/internal/app/app.go
+++ b/internal/app/app.go
@@ -370,7 +370,8 @@ func Run(opt Options) error {
 	bus.SetPendingStore(st)
 	pluginHost.OnCommands = bus.RegisterPluginCommands
 	// hostcaps：hostapi 闭包与进程内插件句柄共用的 owner 作用域能力（EXT-1 批注 1）。
-	caps := hostcaps{st: st, pipe: pipe, set: setSvc}
+	authzSlot := &projectAuthz{}
+	caps := hostcaps{st: st, pipe: pipe, set: setSvc, authz: authzSlot}
 	applyCompiled(skillsRoot, bus, caps)
 	mgr.OnUsage = func(owner string, tokens int) {
 		budget := int(setSvc.Effective(owner, "").GetNumber("llm.dailyTokenBudget", 0))
@@ -399,6 +400,8 @@ func Run(opt Options) error {
 	}
 
 	srv := server.New(st, mgr, reg, profSvc, setSvc, pluginHost)
+	// EXT-8：装载期注册的资源授权适配器注入读取入口（未注册=默认拒绝，行为不变）。
+	srv.SetProjectAuthorizer(authzSlot.Authorize)
 	srv.Workflows = wfReg
 	mgr.SetWorkflows(wfReg)
 	srv.Cards = cardSvc
diff --git a/internal/app/compiled.go b/internal/app/compiled.go
index c38a76e..9e75970 100644
--- a/internal/app/compiled.go
+++ b/internal/app/compiled.go
@@ -3,6 +3,7 @@ package app
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"log"
 	"os"
@@ -65,6 +66,11 @@ func (r compiledRegistry) AddCommand(spec json.RawMessage) error {
 	return r.bus.RegisterPluginCommands([]json.RawMessage{spec})
 }
 
+// RegisterResourceAuthorizer 声明式扩展无宿主进程内代码，不能提供回调（fail-closed）。
+func (r compiledRegistry) RegisterResourceAuthorizer(extension.ResourceAuthorizer) error {
+	return errors.New("extension: declarative plugins cannot register resource authorizers")
+}
+
 func (r compiledRegistry) Note(kind, name string, payload json.RawMessage) error {
 	log.Printf("extension: note %s %s (%d bytes)", kind, name, len(payload))
 	return nil
diff --git a/internal/app/hostcaps.go b/internal/app/hostcaps.go
index 99d00a7..8ef6857 100644
--- a/internal/app/hostcaps.go
+++ b/internal/app/hostcaps.go
@@ -1,8 +1,10 @@
 package app
 
 import (
+	"agent-system-backend/pkg/extension"
 	"context"
 	"fmt"
+	"sync"
 
 	"agent-system-backend/internal/ingest"
 	"agent-system-backend/internal/rag"
@@ -16,9 +18,37 @@ import (
 // 同一实现同时服务 hostapi.Server 的 Search/Complete 闭包与进程内
 // inprocHost（EXT-1 批注 1：复用现有 owner 作用域函数，不新造句柄）。
 type hostcaps struct {
-	st   *store.Store
-	pipe *rag.Pipeline
-	set  *settings.Service
+	st    *store.Store
+	pipe  *rag.Pipeline
+	set   *settings.Service
+	authz *projectAuthz // EXT-8 适配器槽（共享指针；首个注册者生效）
+}
+
+// projectAuthz EXT-8 资源授权适配器槽：进程内扩展注册，组合根装配进 Server。
+type projectAuthz struct {
+	mu     sync.Mutex
+	holder string // 持有者 pluginID（首个注册者生效）
+	fn     extension.ResourceAuthorizer
+}
+
+func (a *projectAuthz) set(pluginID string, fn extension.ResourceAuthorizer) {
+	a.mu.Lock()
+	defer a.mu.Unlock()
+	if a.fn != nil {
+		return // 首个注册者生效；后来者忽略（调用方经日志可查）
+	}
+	a.holder, a.fn = pluginID, fn
+}
+
+// Authorize owner×project 共享读取判定；未注册一律 false（默认拒绝）。
+func (a *projectAuthz) Authorize(owner string, projectID core.ID) (bool, error) {
+	a.mu.Lock()
+	fn := a.fn
+	a.mu.Unlock()
+	if fn == nil || owner == "" || projectID == "" {
+		return false, nil
+	}
+	return fn(owner, projectID)
 }
 
 // search owner 作用域混合检索；projectID/topK 为空/0 时用管线默认值。
diff --git a/internal/server/resource_authz_test.go b/internal/server/resource_authz_test.go
new file mode 100644
index 0000000..fae9e35
--- /dev/null
+++ b/internal/server/resource_authz_test.go
@@ -0,0 +1,124 @@
+package server
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"mime/multipart"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	core "agent-system-core"
+)
+
+// EXT-8 资源授权适配器（红测：基础设施已就位、读取入口尚未咨询）——
+// 默认拒绝保持现状；注册适配器后同项目成员可读共享资源、跨项目仍拒。
+func TestProjectResourceAuthorizerSharesReads(t *testing.T) {
+	srv, st := newAuthTestServer(t)
+	h := srv.Handler()
+
+	alice, err := st.CreateAPIKey("alice", "e2e")
+	if err != nil {
+		t.Fatal(err)
+	}
+	bob, err := st.CreateAPIKey("bob", "e2e")
+	if err != nil {
+		t.Fatal(err)
+	}
+	carol, err := st.CreateAPIKey("carol", "e2e")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// alice 建项目并上传一份工件（owner=alice）。
+	prj := struct{ Name string `json:"name"` }{Name: "EXT8 共享项目"}
+	req := httptest.NewRequest(http.MethodPost, "/api/projects", bytes.NewReader(marshal(t, prj)))
+	req.Header.Set("Authorization", "Bearer "+alice)
+	rec := httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("create project: %d %s", rec.Code, rec.Body.String())
+	}
+	pid := decodeField(t, rec.Body.Bytes(), "id")
+
+	var buf bytes.Buffer
+	mw := multipart.NewWriter(&buf)
+	fw, _ := mw.CreateFormFile("file", "共享说明.txt")
+	fw.Write([]byte("SHARED-CONTENT"))
+	mw.Close()
+	req = httptest.NewRequest(http.MethodPost, "/api/projects/"+pid+"/uploads", &buf)
+	req.Header.Set("Authorization", "Bearer "+alice)
+	req.Header.Set("Content-Type", mw.FormDataContentType())
+	rec = httptest.NewRecorder()
+	h.ServeHTTP(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("upload: %d %s", rec.Code, rec.Body.String())
+	}
+	aid := decodeField(t, rec.Body.Bytes(), "artifactId")
+
+	get := func(key, path string) *httptest.ResponseRecorder {
+		req := httptest.NewRequest(http.MethodGet, path, nil)
+		req.Header.Set("Authorization", "Bearer "+key)
+		rec := httptest.NewRecorder()
+		h.ServeHTTP(rec, req)
+		return rec
+	}
+
+	// 默认拒绝（未注册适配器）：bob 任何读取都是 NotFound，不泄露存在性。
+	for _, path := range []string{"/api/projects/" + pid, "/api/projects/" + pid + "/artifacts", "/api/artifacts/" + aid, "/api/artifacts/" + aid + "/content"} {
+		if rec := get(bob, path); rec.Code != http.StatusNotFound {
+			t.Fatalf("default-deny: %s = %d, want 404", path, rec.Code)
+		}
+	}
+
+	// 注册适配器：bob 对该项目有共享授权；carol 无。
+	srv.SetProjectAuthorizer(func(owner string, projectID core.ID) (bool, error) {
+		return owner == "bob" && string(projectID) == pid, nil
+	})
+
+	if rec := get(bob, "/api/projects/"+pid); rec.Code != http.StatusOK {
+		t.Fatalf("shared project read: %d %s", rec.Code, rec.Body.String())
+	}
+	if rec := get(bob, "/api/artifacts/"+aid); rec.Code != http.StatusOK {
+		t.Fatalf("shared artifact meta: %d %s", rec.Code, rec.Body.String())
+	}
+	rec = get(bob, "/api/artifacts/"+aid+"/content")
+	if rec.Code != http.StatusOK || rec.Body.String() != "SHARED-CONTENT" {
+		t.Fatalf("shared artifact content: %d %q", rec.Code, rec.Body.String())
+	}
+	rec = get(bob, "/api/projects/"+pid+"/artifacts")
+	if rec.Code != http.StatusOK || !bytes.Contains(rec.Body.Bytes(), []byte(aid)) {
+		t.Fatalf("shared artifact list: %d %s", rec.Code, rec.Body.String())
+	}
+
+	// 跨项目/未授权用户与错误路径仍拒（NotFound；错误回调 fail-closed）。
+	for _, path := range []string{"/api/projects/" + pid, "/api/artifacts/" + aid, "/api/artifacts/" + aid + "/content"} {
+		if rec := get(carol, path); rec.Code != http.StatusNotFound {
+			t.Fatalf("carol must stay denied: %s = %d", path, rec.Code)
+		}
+	}
+	srv.SetProjectAuthorizer(func(string, core.ID) (bool, error) { return false, io.ErrClosedPipe })
+	if rec := get(bob, "/api/projects/"+pid); rec.Code != http.StatusNotFound {
+		t.Fatalf("authorizer error must fail closed: %d", rec.Code)
+	}
+}
+
+func marshal(t *testing.T, v any) []byte {
+	t.Helper()
+	b, err := json.Marshal(v)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return b
+}
+
+func decodeField(t *testing.T, body []byte, field string) string {
+	t.Helper()
+	var m map[string]any
+	if err := json.Unmarshal(body, &m); err != nil {
+		t.Fatalf("decode %s: %v (%s)", field, err, body)
+	}
+	return fmt.Sprint(m[field])
+}
diff --git a/internal/server/server.go b/internal/server/server.go
index bf5c184..ad2bfde 100644
--- a/internal/server/server.go
+++ b/internal/server/server.go
@@ -57,6 +57,24 @@ type Server struct {
 	static      fs.FS
 	// Subscribe 注入 bus 订阅（事件在线转发；重放走 store 游标）。
 	Subscribe func(conversationID string) (<-chan core.StreamEvent, func())
+	// ProjectAuthz EXT-8 资源授权适配器（组合根注入；nil=未注册，读取入口
+	// owner 自有判定未命中即 NotFound——与未扩展基座行为一致）。
+	ProjectAuthz func(owner string, projectID core.ID) (bool, error)
+}
+
+// SetProjectAuthorizer 组合根在装载扩展后注入 EXT-8 适配器。
+func (s *Server) SetProjectAuthorizer(fn func(owner string, projectID core.ID) (bool, error)) {
+	s.ProjectAuthz = fn
+}
+
+// authorizeSharedProject 读取路径的共享判定：适配器未注册或拒绝/出错一律 false
+//（fail-closed；错误不区分，避免泄露存在性）。
+func (s *Server) authorizeSharedProject(owner string, projectID core.ID) bool {
+	if s.ProjectAuthz == nil {
+		return false
+	}
+	ok, err := s.ProjectAuthz(owner, projectID)
+	return err == nil && ok
 }
 
 func New(st *store.Store, mgr *runmgr.Manager, reg *tools.Registry, p *profiles.Service, s *settings.Service, ph *plugins.Host) *Server {
diff --git a/pkg/extension/extension.go b/pkg/extension/extension.go
index 835590c..642d47f 100644
--- a/pkg/extension/extension.go
+++ b/pkg/extension/extension.go
@@ -6,14 +6,22 @@ import (
 	"encoding/json"
 	"errors"
 	"sync"
+
+	core "agent-system-core"
 )
 
 // SurfaceVersion 是本包导出面的实验版本。变更导出符号必须同时更新 surface.txt。
-const SurfaceVersion = "2.0.0-experimental"
+// 2.1.0-experimental：EXT-8 新增 ResourceAuthorizer 与 Registry.RegisterResourceAuthorizer。
+const SurfaceVersion = "2.1.0-experimental"
 
 // ErrNotLinked 表示进程没有空白导入 link 包，Main 无法启动服务。
 var ErrNotLinked = errors.New("extension: runner not linked; blank-import agent-system-backend/pkg/extension/link")
 
+// ResourceAuthorizer 是 EXT-8 资源授权适配器：基座在 owner 自有资源判定未命中时，
+// 回调询问「owner 对 projectID 是否有共享读取授权」。只回答布尔，不接触基座内部
+// 状态；返回 error 视为拒绝（fail-closed）。仅作用于读取路径，写路径一律 owner 自有。
+type ResourceAuthorizer func(owner string, projectID core.ID) (bool, error)
+
 // Registry 是进程内扩展的注册口。实现在基座内部，对下游只暴露这些方法。
 type Registry interface {
 	AddSkill(name, markdown string) error
@@ -22,6 +30,9 @@ type Registry interface {
 	// 基座在分发时按请求 Owner 构造 Host 句柄调用 h。
 	AddCommandHandler(spec json.RawMessage, h Handler) error
 	Note(kind, name string, payload json.RawMessage) error
+	// RegisterResourceAuthorizer 注册 EXT-8 资源授权适配器（进程内扩展）；
+	// 首个注册者生效。声明式扩展不支持（回调需宿主进程内代码）。
+	RegisterResourceAuthorizer(authz ResourceAuthorizer) error
 }
 
 // InProc 是随下游二进制编译进来的扩展。
diff --git a/pkg/extension/surface.txt b/pkg/extension/surface.txt
index 834d0ed..c7f5658 100644
--- a/pkg/extension/surface.txt
+++ b/pkg/extension/surface.txt
@@ -26,7 +26,9 @@ Registry.AddCommand
 Registry.AddCommandHandler
 Registry.AddSkill
 Registry.Note
+Registry.RegisterResourceAuthorizer
 Request
 ResetCompiled
+ResourceAuthorizer
 SetRunner
 SurfaceVersion