diff --git a/internal/server/handlers.go b/internal/server/handlers.go
index 79069c3b..b11de1a9 100644
--- a/internal/server/handlers.go
+++ b/internal/server/handlers.go
@@ -1067,6 +1067,7 @@ type upsertChatSessionRequest struct {
 }
 
 // handleUpsertChatSession 注册或更新会话元数据（立项/成员加入时同步）。
+// 默认归属认证用户本人；项目管理员可为其他成员代注册（防水平越权）。
 func (s *Server) handleUpsertChatSession(w http.ResponseWriter, r *http.Request) {
 	if s.ctxMgr == nil {
 		writeSafeError(w, r, http.StatusServiceUnavailable, "context manager not initialized")
@@ -1086,9 +1087,32 @@ func (s *Server) handleUpsertChatSession(w http.ResponseWriter, r *http.Request)
 		writeSafeError(w, r, http.StatusBadRequest, "missing session_id")
 		return
 	}
-	req.UserID = user.ID
 
-	summary, err := s.ctxMgr.EnsureChatSessionOwned(r.Context(), req.SessionID, req.UserID, req.ProjectID, req.Title)
+	ownerID := user.ID
+	if req.UserID > 0 && req.UserID != user.ID {
+		if req.ProjectID <= 0 {
+			writeJSONResponse(w, http.StatusBadRequest, map[string]string{
+				"error_code": "ERR_INVALID_PARAM",
+				"message":    "代注册他人会话时必须指定 project_id",
+			})
+			return
+		}
+		can, err := s.authzSvc.CanManageProjectMembers(r.Context(), req.ProjectID, user.ID, user.RoleID)
+		if err != nil {
+			writeSafeError(w, r, http.StatusInternalServerError, err.Error())
+			return
+		}
+		if !can {
+			writeJSONResponse(w, http.StatusForbidden, map[string]string{
+				"error_code": "ERR_FORBIDDEN",
+				"message":    "无权为其他用户注册项目会话",
+			})
+			return
+		}
+		ownerID = req.UserID
+	}
+
+	summary, err := s.ctxMgr.EnsureChatSessionOwned(r.Context(), req.SessionID, ownerID, req.ProjectID, req.Title)
 	if err != nil {
 		if errors.Is(err, ctxmgr.ErrSessionOwnerMismatch) {
 			writeJSONResponse(w, http.StatusForbidden, map[string]string{
diff --git a/internal/server/project_members_handlers.go b/internal/server/project_members_handlers.go
index e20328ba..a3eed9de 100644
--- a/internal/server/project_members_handlers.go
+++ b/internal/server/project_members_handlers.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"log"
 	"net/http"
 	"strconv"
@@ -128,9 +129,27 @@ func (s *Server) handleAddProjectMember(w http.ResponseWriter, r *http.Request,
 		writeDutySyncError(w)
 		return
 	}
+	s.ensureMemberChatSession(r.Context(), projectID, req.UserID)
 	writeJSONResponse(w, http.StatusCreated, map[string]bool{"success": true})
 }
 
+// ensureMemberChatSession 为项目成员补齐私有会话（sess-p{id}-u{uid}），失败仅记日志。
+func (s *Server) ensureMemberChatSession(ctx context.Context, projectID, memberUserID int64) {
+	if s == nil || s.ctxMgr == nil || projectID <= 0 || memberUserID <= 0 {
+		return
+	}
+	title := ""
+	if s.pwSvc != nil {
+		if proj, err := s.pwSvc.GetProject(ctx, projectID, 0); err == nil && proj != nil {
+			title = proj.Name
+		}
+	}
+	sessionID := fmt.Sprintf("sess-p%d-u%d", projectID, memberUserID)
+	if _, err := s.ctxMgr.EnsureChatSessionOwned(ctx, sessionID, memberUserID, projectID, title); err != nil {
+		log.Printf("[members] ensure chat session for project=%d user=%d failed: %v", projectID, memberUserID, err)
+	}
+}
+
 func (s *Server) handleUpdateProjectMember(w http.ResponseWriter, r *http.Request, user *auth.UserAccount, projectID int64) {
 	if !s.requireProjectMemberManage(w, r, user, projectID) {
 		return