diff --git a/netx_api/topology_views_tree.py b/netx_api/topology_views_tree.py
index 2892573..d94c9a7 100644
--- a/netx_api/topology_views_tree.py
+++ b/netx_api/topology_views_tree.py
@@ -18,6 +18,7 @@ from .models import (
     TopoViewEdgeStyle,
     TopoViewNode,
     UmeInventoryNE,
+    UmeTopoNode,
 )
 from .topology_common import (
     PHYSICAL_VIEW_NAME,
@@ -28,6 +29,9 @@ from .topology_common import (
     _normalize_edge_status,
     _utcnow,
 )
+
+# Manual top-level「根」auto-spawns this unique L2 canvas (mirrors UME World / World).
+MANUAL_ROOT_MAP_NAME = "根图"
 from .topology_fabric import (
     _edge_out,
     _fabric_match_score,
@@ -261,6 +265,50 @@ def create_folder(db: Session, body: TopologyFolderCreate) -> TopologyFolderOut:
         parent = drill
         parent_kind = "region"
 
+    # Manual 根 (top-level nav): unique L2「根图」only — further creates remount under it.
+    if parent_kind == "region" and str(parent.parent_id or "") == str(root.id):
+        existing_l2 = (
+            db.query(TopoFolder)
+            .filter(TopoFolder.parent_id == parent.id, TopoFolder.kind == "region")
+            .order_by(TopoFolder.sort_order.asc(), TopoFolder.created_at.asc())
+            .all()
+        )
+        if existing_l2:
+            parent = existing_l2[0]
+            parent_kind = "region"
+        else:
+            # Legacy 根 without 根图 — heal then remount.
+            heal_now = _utcnow()
+            root_map = TopoFolder(
+                id=uuid4().hex,
+                parent_id=parent.id,
+                kind="region",
+                name=MANUAL_ROOT_MAP_NAME,
+                sort_order=0,
+                is_system=True,
+                created_at=heal_now,
+                updated_at=heal_now,
+            )
+            db.add(root_map)
+            db.flush()
+            db.add(
+                TopoView(
+                    id=uuid4().hex,
+                    folder_id=root_map.id,
+                    kind=VIEW_KIND_PHYSICAL,
+                    role="core",
+                    name=MANUAL_ROOT_MAP_NAME,
+                    remark="",
+                    sort_order=0,
+                    filter={},
+                    viewport={},
+                    created_at=heal_now,
+                    updated_at=heal_now,
+                )
+            )
+            db.flush()
+            parent = root_map
+            parent_kind = "region"
     now = _utcnow()
     row = TopoFolder(
         id=uuid4().hex,
@@ -274,26 +322,68 @@ def create_folder(db: Session, body: TopologyFolderCreate) -> TopologyFolderOut:
     )
     db.add(row)
     db.flush()
-    # Nested / any new region gets a blank physical canvas so the tree can open it.
-    phys = TopoView(
-        id=uuid4().hex,
-        folder_id=row.id,
-        kind=VIEW_KIND_PHYSICAL,
-        role="core",
-        name=name[:200] or "Topology",
-        remark="",
-        sort_order=0,
-        filter={},
-        viewport={},
-        created_at=now,
-        updated_at=now,
-    )
-    db.add(phys)
-    # Nested region: place a building icon on the parent's canvas (region === canvas).
-    if parent_kind == "region":
-        from .topology_region_canvas import place_child_region_on_parent_canvas
 
-        place_child_region_on_parent_canvas(db, parent, row)
+    if parent_kind == "root":
+        # 「根」nav container + auto unique「根图」canvas (UME World / World pattern).
+        root_map = TopoFolder(
+            id=uuid4().hex,
+            parent_id=row.id,
+            kind="region",
+            name=MANUAL_ROOT_MAP_NAME,
+            sort_order=0,
+            is_system=True,
+            created_at=now,
+            updated_at=now,
+        )
+        db.add(root_map)
+        db.flush()
+        db.add(
+            TopoView(
+                id=uuid4().hex,
+                folder_id=root_map.id,
+                kind=VIEW_KIND_PHYSICAL,
+                role="core",
+                name=MANUAL_ROOT_MAP_NAME,
+                remark="",
+                sort_order=0,
+                filter={},
+                viewport={},
+                created_at=now,
+                updated_at=now,
+            )
+        )
+    elif parent_kind == "region":
+        # Nested under 根图 / deeper canvas: region === canvas + icon on parent.
+        phys = TopoView(
+            id=uuid4().hex,
+            folder_id=row.id,
+            kind=VIEW_KIND_PHYSICAL,
+            role="core",
+            name=name[:200] or "Topology",
+            remark="",
+            sort_order=0,
+            filter={},
+            viewport={},
+            created_at=now,
+            updated_at=now,
+        )
+        db.add(phys)
+        db.flush()
+        parent_has_phys = (
+            db.query(TopoView.id)
+            .filter(TopoView.folder_id == parent.id, TopoView.kind == VIEW_KIND_PHYSICAL)
+            .first()
+            is not None
+        )
+        if parent_has_phys:
+            from .topology_region_canvas import place_child_region_on_parent_canvas
+
+            place_child_region_on_parent_canvas(db, parent, row)
+        else:
+            ensure_region_physical_view(db, parent.id, commit=False)
+            from .topology_region_canvas import place_child_region_on_parent_canvas
+
+            place_child_region_on_parent_canvas(db, parent, row)
     db.flush()
     reconcile_world_flat_view(db)
     db.commit()
@@ -338,28 +428,41 @@ def update_folder(db: Session, folder_id: str, body: TopologyFolderUpdate) -> To
 
 
 def delete_folder(db: Session, folder_id: str, *, force: bool = False) -> dict[str, Any]:
-    """Delete a region and cascade-delete its maps.
+    """Delete a region and cascade-delete nested regions + maps.
 
     ``force`` is accepted for API compatibility; cascade always runs.
+    System L2「根图」may be removed only as part of cascading from its parent「根」.
     """
     row = _get_folder_or_404(db, folder_id)
-    if str(row.kind or "") == "root" or bool(row.is_system):
+    if str(row.kind or "") == "root":
+        raise HTTPException(status_code=400, detail="cannot_delete_system_folder")
+    if bool(row.is_system):
         raise HTTPException(status_code=400, detail="cannot_delete_system_folder")
     _ = force
     from .topology_region_canvas import remove_region_canvas_placements
 
-    remove_region_canvas_placements(db, row.id)
-    views = db.query(TopoView).filter(TopoView.folder_id == row.id).all()
-    for v in views:
-        db.query(TopoViewEdgeStyle).filter(TopoViewEdgeStyle.view_id == v.id).delete(
-            synchronize_session=False
+    def _purge_folder(folder: TopoFolder) -> None:
+        kids = (
+            db.query(TopoFolder)
+            .filter(TopoFolder.parent_id == folder.id)
+            .all()
         )
-        db.query(TopoViewNode).filter(TopoViewNode.view_id == v.id).delete(
-            synchronize_session=False
-        )
-        db.delete(v)
-    db.flush()
-    db.delete(row)
+        for kid in kids:
+            _purge_folder(kid)
+        remove_region_canvas_placements(db, folder.id)
+        views = db.query(TopoView).filter(TopoView.folder_id == folder.id).all()
+        for v in views:
+            db.query(TopoViewEdgeStyle).filter(TopoViewEdgeStyle.view_id == v.id).delete(
+                synchronize_session=False
+            )
+            db.query(TopoViewNode).filter(TopoViewNode.view_id == v.id).delete(
+                synchronize_session=False
+            )
+            db.delete(v)
+        db.flush()
+        db.delete(folder)
+
+    _purge_folder(row)
     from .ume_topology_world import reconcile_world_flat_view
 
     reconcile_world_flat_view(db)
@@ -371,38 +474,61 @@ def get_topology_tree(db: Session) -> TopologyTreeOut:
     bootstrap_topology_tree(db)
     folders = db.query(TopoFolder).order_by(TopoFolder.sort_order.asc(), TopoFolder.name.asc()).all()
     views = db.query(TopoView).order_by(TopoView.sort_order.asc(), TopoView.name.asc()).all()
-    nc_map: dict[str, int] = {}
-    for vid, cnt in (
-        db.query(TopoViewNode.view_id, func.count(TopoViewNode.id))
-        .group_by(TopoViewNode.view_id)
-        .all()
-    ):
-        nc_map[str(vid)] = int(cnt or 0)
-    region_icon_map: dict[str, int] = {}
-    for vid, cnt in (
-        db.query(TopoViewNode.view_id, func.count(TopoViewNode.id))
-        .filter(TopoViewNode.fabric_node_id.like("region:%"))
-        .group_by(TopoViewNode.view_id)
-        .all()
-    ):
-        region_icon_map[str(vid)] = int(cnt or 0)
-
-    # UME canvases are virtual (no TopoViewNode membership) — count fabric MEs instead.
-    ume_ne_by_sbn: dict[str, int] = {}
-    ume_ne_by_folder: dict[str, int] = {}
-    ume_ne_total = 0
-    for fn in (
-        db.query(TopoFabricNode)
+    # Cheap directory counts — never hydrate 15k fabric rows (attrs JSON) on tree load.
+    # Full inventory scans belong only to the world flat map graph.
+    nc_map: dict[str, int] = {
+        str(vid): int(cnt or 0)
+        for vid, cnt in (
+            db.query(TopoViewNode.view_id, func.count(TopoViewNode.id))
+            .group_by(TopoViewNode.view_id)
+            .all()
+        )
+    }
+    region_icon_map: dict[str, int] = {
+        str(vid): int(cnt or 0)
+        for vid, cnt in (
+            db.query(TopoViewNode.view_id, func.count(TopoViewNode.id))
+            .filter(TopoViewNode.fabric_node_id.like("region:%"))
+            .group_by(TopoViewNode.view_id)
+            .all()
+        )
+    }
+    ume_ne_by_folder: dict[str, int] = {
+        str(fid): int(cnt or 0)
+        for fid, cnt in (
+            db.query(TopoFabricNode.region_folder_id, func.count(TopoFabricNode.id))
+            .filter(
+                TopoFabricNode.ume_ne_id.isnot(None),
+                TopoFabricNode.ume_ne_id != "",
+                TopoFabricNode.region_folder_id.isnot(None),
+                TopoFabricNode.region_folder_id != "",
+            )
+            .group_by(TopoFabricNode.region_folder_id)
+            .all()
+        )
+        if str(fid or "").strip()
+    }
+    # Direct ME counts by UME parent SBN (level-by-level; not full subtree rollup).
+    ume_ne_by_sbn: dict[str, int] = {
+        str(parent): int(cnt or 0)
+        for parent, cnt in (
+            db.query(UmeTopoNode.parent_node, func.count(UmeTopoNode.node_id))
+            .filter(
+                UmeTopoNode.node_type == "TOPO_NODE_ME",
+                UmeTopoNode.parent_node.isnot(None),
+                UmeTopoNode.parent_node != "",
+            )
+            .group_by(UmeTopoNode.parent_node)
+            .all()
+        )
+        if str(parent or "").strip()
+    }
+    ume_ne_total = int(
+        db.query(func.count(TopoFabricNode.id))
         .filter(TopoFabricNode.ume_ne_id.isnot(None), TopoFabricNode.ume_ne_id != "")
-        .all()
-    ):
-        ume_ne_total += 1
-        fid = str(fn.region_folder_id or "").strip()
-        if fid:
-            ume_ne_by_folder[fid] = ume_ne_by_folder.get(fid, 0) + 1
-        sid = str((fn.attrs or {}).get("ume_sbn_id") or "").strip()
-        if sid:
-            ume_ne_by_sbn[sid] = ume_ne_by_sbn.get(sid, 0) + 1
+        .scalar()
+        or 0
+    )
 
     def _view_node_count(v: TopoView) -> int:
         raw = int(nc_map.get(v.id, 0) or 0)
@@ -418,7 +544,7 @@ def get_topology_tree(db: Session) -> TopologyTreeOut:
             sid = str(filt.get("sbn_id") or "").strip()
             if sid:
                 return int(ume_ne_by_sbn.get(sid, 0))
-            # World drill root: all UME MEs.
+            # World drill root: directory hint only (open canvas for real graph).
             if str(filt.get("parent") or "") == "md":
                 return ume_ne_total
             if v.folder_id:
diff --git a/netx_api/ume_topology_apply.py b/netx_api/ume_topology_apply.py
index c7b8dc0..b8f8eab 100644
--- a/netx_api/ume_topology_apply.py
+++ b/netx_api/ume_topology_apply.py
@@ -68,7 +68,10 @@ def apply_ume_topology_to_fabric(db: Session) -> dict[str, Any]:
         .filter(UmeTopoNode.node_type == "TOPO_NODE_ME")
         .all()
     )
-    for tn in me_nodes:
+    # Advisory xact locks + nested savepoints accumulate; commit in batches or PG
+    # hits OutOfMemory / max_locks_per_transaction on ~15k MEs.
+    _NODE_BATCH = 250
+    for i, tn in enumerate(me_nodes, start=1):
         uid = str(tn.ume_ne_id or tn.node_id or "").strip()
         if not uid:
             continue
@@ -118,8 +121,12 @@ def apply_ume_topology_to_fabric(db: Session) -> dict[str, Any]:
             attrs["ume_sbn_id"] = str(tn.parent_node)[:128]
         fn.attrs = attrs
         fabric_by_ume[uid] = fn
+        if i % _NODE_BATCH == 0:
+            db.commit()
+            if i % 2000 == 0:
+                _log.info("ume topology apply nodes progress %s/%s", i, len(me_nodes))
 
-    db.flush()
+    db.commit()
 
     seen_edge_ids: set[str] = set()
     links = db.query(UmeTopoLink).all()
diff --git a/netx_api/ume_topology_world.py b/netx_api/ume_topology_world.py
index 26a51d4..bab29b1 100644
--- a/netx_api/ume_topology_world.py
+++ b/netx_api/ume_topology_world.py
@@ -123,16 +123,21 @@ def get_world_flat_view(db: Session) -> TopoView | None:
     return None
 
 
-def _folder_subtree_ids(db: Session, folder_id: str) -> set[str]:
-    all_folders = db.query(TopoFolder).all()
-    children: dict[str | None, list[str]] = {}
-    for f in all_folders:
-        children.setdefault(f.parent_id, []).append(f.id)
+def _folder_subtree_ids(
+    db: Session,
+    folder_id: str,
+    *,
+    children_map: dict[str | None, list[str]] | None = None,
+) -> set[str]:
+    if children_map is None:
+        children_map = {}
+        for fid, parent_id in db.query(TopoFolder.id, TopoFolder.parent_id).all():
+            children_map.setdefault(parent_id, []).append(fid)
     ids = {folder_id}
     stack = [folder_id]
     while stack:
         cur = stack.pop()
-        for cid in children.get(cur, []):
+        for cid in children_map.get(cur, []):
             if cid not in ids:
                 ids.add(cid)
                 stack.append(cid)
@@ -142,25 +147,28 @@ def _folder_subtree_ids(db: Session, folder_id: str) -> set[str]:
 def _child_region_has_nes(db: Session, child: TopoFolder) -> bool:
     """True when the child region subtree owns at least one fabric NE."""
     ids = _folder_subtree_ids(db, child.id)
-    n = (
-        db.query(TopoFabricNode)
+    if ids and (
+        db.query(TopoFabricNode.id)
         .filter(TopoFabricNode.region_folder_id.in_(list(ids)))
         .limit(1)
         .first()
-    )
-    if n is not None:
+        is not None
+    ):
         return True
+    # Cheap fallback: direct UME ME under this SBN (never scan all fabric attrs).
     ref = str(getattr(child, "external_ref", None) or "").strip()
     if ref and not ref.startswith("ume:"):
-        for fn in (
-            db.query(TopoFabricNode)
-            .filter(TopoFabricNode.ume_ne_id.isnot(None), TopoFabricNode.ume_ne_id != "")
-            .all()
+        if (
+            db.query(UmeTopoNode.node_id)
+            .filter(
+                UmeTopoNode.node_type == "TOPO_NODE_ME",
+                UmeTopoNode.parent_node == ref,
+            )
+            .limit(1)
+            .first()
+            is not None
         ):
-            if str((fn.attrs or {}).get("ume_sbn_id") or "") == ref:
-                return True
-            if str(fn.region_folder_id or "") == child.id:
-                return True
+            return True
     return False
 
 
@@ -180,7 +188,38 @@ def world_map_should_exist(db: Session) -> bool:
     )
     if not children:
         return False
-    return any(_child_region_has_nes(db, c) for c in children)
+    children_map: dict[str | None, list[str]] = {}
+    for fid, parent_id in db.query(TopoFolder.id, TopoFolder.parent_id).all():
+        children_map.setdefault(parent_id, []).append(fid)
+    all_ids: set[str] = set()
+    for c in children:
+        all_ids |= _folder_subtree_ids(db, c.id, children_map=children_map)
+    if all_ids and (
+        db.query(TopoFabricNode.id)
+        .filter(TopoFabricNode.region_folder_id.in_(list(all_ids)))
+        .limit(1)
+        .first()
+        is not None
+    ):
+        return True
+    refs = [
+        str(getattr(c, "external_ref", None) or "").strip()
+        for c in children
+        if str(getattr(c, "external_ref", None) or "").strip()
+        and not str(getattr(c, "external_ref", None) or "").startswith("ume:")
+    ]
+    if refs and (
+        db.query(UmeTopoNode.node_id)
+        .filter(
+            UmeTopoNode.node_type == "TOPO_NODE_ME",
+            UmeTopoNode.parent_node.in_(refs),
+        )
+        .limit(1)
+        .first()
+        is not None
+    ):
+        return True
+    return False
 
 
 def reconcile_world_flat_view(db: Session) -> TopoView | None:
diff --git a/netx_api/ume_topology_world_graph.py b/netx_api/ume_topology_world_graph.py
index 2954e7a..2f2e045 100644
--- a/netx_api/ume_topology_world_graph.py
+++ b/netx_api/ume_topology_world_graph.py
@@ -6,11 +6,13 @@ from collections import defaultdict
 from typing import Any
 
 from fastapi import HTTPException
+from sqlalchemy import func, or_
 from sqlalchemy.orm import Session
 
 from .models import TopoFabricEdge, TopoFabricNode, TopoFolder, TopoView, TopoViewNode, UmeTopoNode
 from .topology_common import (
     VIEW_GRAPH_EDGE_HARD_CAP,
+    VIEW_GRAPH_NODE_HARD_CAP,
     _EDGE_STATUS_MISSING,
     _EDGE_STATUS_MISSING_COMPAT,
     _normalize_edge_status,
@@ -29,7 +31,9 @@ from .ume_topology_world import (
     is_world_view,
 )
 
-WORLD_NODE_SOFT_CAP = 8000
+# Keep flat-world responses at the same browser-safe hard cap as other views.
+# (Previously 8000 — loading that into React Flow + API RAM starved the whole host.)
+WORLD_NODE_SOFT_CAP = VIEW_GRAPH_NODE_HARD_CAP
 
 
 def apply_persisted_view_positions(
@@ -122,20 +126,33 @@ def get_level_view_graph(
     if parent_key == "md" or is_world_view(view):
         # Root: SBN whose parent is not another SBN (+ rare direct MEs under MD).
         sbn_ids = {
-            str(n.node_id)
-            for n in db.query(UmeTopoNode).filter(UmeTopoNode.node_type == "TOPO_NODE_SBN").all()
-            if str(n.node_id or "").strip()
+            str(row[0])
+            for row in db.query(UmeTopoNode.node_id).filter(UmeTopoNode.node_type == "TOPO_NODE_SBN").all()
+            if str(row[0] or "").strip()
         }
         child_sbns = [
             n
             for n in db.query(UmeTopoNode).filter(UmeTopoNode.node_type == "TOPO_NODE_SBN").all()
             if str(n.parent_node or "").strip() not in sbn_ids
         ]
-        child_mes = [
-            n
-            for n in db.query(UmeTopoNode).filter(UmeTopoNode.node_type == "TOPO_NODE_ME").all()
-            if str(n.parent_node or "").strip() not in sbn_ids
-        ]
+        # Almost all MEs hang under an SBN; push the exclusion into SQL.
+        if sbn_ids:
+            child_mes = (
+                db.query(UmeTopoNode)
+                .filter(
+                    UmeTopoNode.node_type == "TOPO_NODE_ME",
+                    or_(
+                        UmeTopoNode.parent_node.is_(None),
+                        UmeTopoNode.parent_node == "",
+                        ~UmeTopoNode.parent_node.in_(list(sbn_ids)),
+                    ),
+                )
+                .all()
+            )
+        else:
+            child_mes = (
+                db.query(UmeTopoNode).filter(UmeTopoNode.node_type == "TOPO_NODE_ME").all()
+            )
         level_parent = ""  # MD virtual
     else:
         if not sbn_id and view.folder_id:
@@ -163,77 +180,100 @@ def get_level_view_graph(
             .all()
         )
 
-    # Folder / view lookup for region drill targets
-    folders_by_ref: dict[str, TopoFolder] = {
-        str(f.external_ref): f
-        for f in db.query(TopoFolder)
-        .filter(TopoFolder.external_ref.isnot(None), TopoFolder.external_ref != "")
-        .all()
-        if str(f.external_ref or "").strip() and not str(f.external_ref).startswith("ume:")
-    }
-    level_view_by_sbn: dict[str, TopoView] = {}
-    for v in db.query(TopoView).all():
-        vf = dict(v.filter or {})
-        if vf.get("ume_level") and str(vf.get("sbn_id") or "").strip():
-            level_view_by_sbn[str(vf["sbn_id"])] = v
-
-    # Descendants of each direct child SBN (for logical edge lift + counts)
-    all_sbns = {
-        str(n.node_id): n
-        for n in db.query(UmeTopoNode).filter(UmeTopoNode.node_type == "TOPO_NODE_SBN").all()
-        if str(n.node_id or "").strip()
-    }
-    sbn_children: dict[str, list[str]] = defaultdict(list)
-    for sid, node in all_sbns.items():
-        p = str(node.parent_node or "").strip()
-        if p:
-            sbn_children[p].append(sid)
-
-    def _descendants(root_sid: str) -> set[str]:
-        out = {root_sid}
-        stack = [root_sid]
-        while stack:
-            cur = stack.pop()
-            for cid in sbn_children.get(cur, []):
-                if cid not in out:
-                    out.add(cid)
-                    stack.append(cid)
-        return out
-
+    # --- Level-by-level: only THIS level's direct child SBNs + direct child MEs.
+    # Region badge counts roll up the whole SBN subtree (cheap: 114 SBNs + GROUP BY).
+    # Deep edge lifts still belong to deeper drills or the flat world map.
     child_sbn_ids = [str(s.node_id) for s in child_sbns if str(s.node_id or "").strip()]
-    region_desc: dict[str, set[str]] = {sid: _descendants(sid) for sid in child_sbn_ids}
+    child_sbn_id_set = set(child_sbn_ids)
 
-    # ME → which direct child region (if under a child SBN subtree)
-    me_to_region: dict[str, str] = {}
-    me_uid_to_topo: dict[str, UmeTopoNode] = {}
-    for tn in db.query(UmeTopoNode).filter(UmeTopoNode.node_type == "TOPO_NODE_ME").all():
-        uid = str(tn.ume_ne_id or tn.node_id or "").strip()
-        if not uid:
-            continue
-        me_uid_to_topo[uid] = tn
-        parent = str(tn.parent_node or "").strip()
+    folders_by_ref: dict[str, TopoFolder] = {}
+    if child_sbn_id_set:
+        for f in (
+            db.query(TopoFolder)
+            .filter(TopoFolder.external_ref.in_(list(child_sbn_id_set)))
+            .all()
+        ):
+            ref = str(f.external_ref or "").strip()
+            if ref:
+                folders_by_ref[ref] = f
+
+    level_view_id_by_sbn: dict[str, str] = {}
+    if child_sbn_id_set:
+        for vid, filt in db.query(TopoView.id, TopoView.filter).all():
+            vf = dict(filt or {})
+            sid = str(vf.get("sbn_id") or "").strip()
+            if vf.get("ume_level") and sid in child_sbn_id_set:
+                level_view_id_by_sbn[sid] = str(vid)
+
+    # Subtree ME counts for each direct child region (badge), without hydrating all MEs.
+    region_me_counts: dict[str, int] = {sid: 0 for sid in child_sbn_ids}
+    if child_sbn_id_set:
+        sbn_parent: dict[str, str] = {
+            str(nid): str(parent or "").strip()
+            for nid, parent in db.query(UmeTopoNode.node_id, UmeTopoNode.parent_node)
+            .filter(UmeTopoNode.node_type == "TOPO_NODE_SBN")
+            .all()
+            if str(nid or "").strip()
+        }
+        sbn_children: dict[str, list[str]] = defaultdict(list)
+        for sid, parent in sbn_parent.items():
+            if parent:
+                sbn_children[parent].append(sid)
+
+        def _descendants(root_sid: str) -> set[str]:
+            out = {root_sid}
+            stack = [root_sid]
+            while stack:
+                cur = stack.pop()
+                for cid in sbn_children.get(cur, []):
+                    if cid not in out:
+                        out.add(cid)
+                        stack.append(cid)
+            return out
+
+        region_desc: dict[str, set[str]] = {sid: _descendants(sid) for sid in child_sbn_ids}
+        me_by_parent: dict[str, int] = {
+            str(parent): int(cnt or 0)
+            for parent, cnt in (
+                db.query(UmeTopoNode.parent_node, func.count())
+                .filter(
+                    UmeTopoNode.node_type == "TOPO_NODE_ME",
+                    UmeTopoNode.parent_node.isnot(None),
+                    UmeTopoNode.parent_node != "",
+                )
+                .group_by(UmeTopoNode.parent_node)
+                .all()
+            )
+            if str(parent or "").strip()
+        }
         for rid, desc in region_desc.items():
-            if parent in desc:
-                me_to_region[uid] = rid
-                break
+            region_me_counts[rid] = sum(me_by_parent.get(p, 0) for p in desc)
 
-    fabric_by_ume: dict[str, TopoFabricNode] = {
-        str(n.ume_ne_id): n
-        for n in db.query(TopoFabricNode).filter(TopoFabricNode.ume_ne_id.isnot(None)).all()
-        if str(n.ume_ne_id or "").strip()
-    }
+    direct_me_uids = [
+        uid
+        for uid in (str(tn.ume_ne_id or tn.node_id or "").strip() for tn in child_mes)
+        if uid
+    ]
+    fabric_by_ume: dict[str, TopoFabricNode] = {}
+    if direct_me_uids:
+        for n in (
+            db.query(TopoFabricNode)
+            .filter(TopoFabricNode.ume_ne_id.in_(direct_me_uids))
+            .all()
+        ):
+            uid = str(n.ume_ne_id or "").strip()
+            if uid:
+                fabric_by_ume[uid] = n
 
     nodes_out: list[ViewNodeOut] = []
-    # Region nodes
-    region_node_ids: dict[str, str] = {}  # sbn_id -> fabric_node_id used in graph
+    region_node_ids: dict[str, str] = {}
     for sbn in child_sbns:
         sid = str(sbn.node_id or "").strip()
         if not sid:
             continue
         folder = folders_by_ref.get(sid)
-        child_view = level_view_by_sbn.get(sid)
-        # Count MEs under this region tree
-        n_me = sum(1 for uid, rid in me_to_region.items() if rid == sid)
+        child_view_id = level_view_id_by_sbn.get(sid, "")
+        n_me = int(region_me_counts.get(sid, 0))
         nid = f"region:{sid}"
         region_node_ids[sid] = nid
         label = (sbn.user_label or (folder.name if folder else sid) or sid)[:256]
@@ -254,14 +294,13 @@ def get_level_view_graph(
                 device_type="region",
                 kind="region",
                 folder_id=folder.id if folder else "",
-                view_id=child_view.id if child_view else "",
+                view_id=child_view_id,
                 node_count=n_me,
             )
         )
 
-    # Direct ME nodes (local coords)
     direct_me_fids: set[str] = set()
-    me_fid_by_uid: dict[str, str] = {}
+    me_uid_to_fid: dict[str, str] = {}
     for tn in child_mes:
         uid = str(tn.ume_ne_id or tn.node_id or "").strip()
         if not uid:
@@ -270,7 +309,7 @@ def get_level_view_graph(
         if fn is None:
             continue
         direct_me_fids.add(fn.id)
-        me_fid_by_uid[uid] = fn.id
+        me_uid_to_fid[uid] = fn.id
         lx = float(tn.x_pos) if tn.x_pos is not None else float(fn.attrs or {}).get("ume_local_x") or 0.0
         ly = float(tn.y_pos) if tn.y_pos is not None else float(fn.attrs or {}).get("ume_local_y") or 0.0
         nodes_out.append(
@@ -290,42 +329,35 @@ def get_level_view_graph(
             )
         )
 
-    # Edges: physical among direct MEs; logical lifts across regions
     st = str(status or "active").strip().lower() or "active"
     st_norm = _normalize_edge_status(st)
-    eq = db.query(TopoFabricEdge).filter(TopoFabricEdge.layer == "physical")
-    if st_norm == _EDGE_STATUS_MISSING:
-        eq = eq.filter(TopoFabricEdge.status.in_(list(_EDGE_STATUS_MISSING_COMPAT)))
-    else:
-        eq = eq.filter(TopoFabricEdge.status == st_norm)
-
-    # Map fabric id → ume ne id
-    fid_to_uid = {fn.id: uid for uid, fn in fabric_by_ume.items()}
-
-    def _endpoint_on_canvas(fid: str) -> str | None:
-        """Return canvas node id for a fabric endpoint, or None if outside this level."""
-        if fid in direct_me_fids:
-            return fid
-        uid = fid_to_uid.get(fid, "")
-        rid = me_to_region.get(uid, "")
-        if rid and rid in region_node_ids:
-            return region_node_ids[rid]
-        return None
+    status_filter = (
+        list(_EDGE_STATUS_MISSING_COMPAT)
+        if st_norm == _EDGE_STATUS_MISSING
+        else [st_norm]
+    )
 
     physical: list[ViewEdgeOut] = []
-    logical_count: dict[tuple[str, str], int] = defaultdict(int)
-    for e in eq.limit(VIEW_GRAPH_EDGE_HARD_CAP * 20).all():
-        a = _endpoint_on_canvas(e.a_node_id)
-        b = _endpoint_on_canvas(e.b_node_id)
-        if not a or not b or a == b:
-            continue
-        # Both direct MEs → physical
-        if a in direct_me_fids and b in direct_me_fids:
+    if direct_me_fids:
+        direct_list = list(direct_me_fids)
+        for e in (
+            db.query(TopoFabricEdge)
+            .filter(
+                TopoFabricEdge.layer == "physical",
+                TopoFabricEdge.status.in_(status_filter),
+                TopoFabricEdge.a_node_id.in_(direct_list),
+                TopoFabricEdge.b_node_id.in_(direct_list),
+            )
+            .limit(VIEW_GRAPH_EDGE_HARD_CAP + 1)
+            .all()
+        ):
+            if e.a_node_id == e.b_node_id:
+                continue
             physical.append(
                 ViewEdgeOut(
                     id=e.id,
-                    a_node_id=a,
-                    b_node_id=b,
+                    a_node_id=e.a_node_id,
+                    b_node_id=e.b_node_id,
                     a_port=e.a_port or "",
                     b_port=e.b_port or "",
                     source=e.source or "lldp",
@@ -334,9 +366,58 @@ def get_level_view_graph(
                     discovered_at=e.discovered_at,
                 )
             )
-        else:
-            key = (a, b) if a < b else (b, a)
-            logical_count[key] += 1
+
+    # Logical lifts only among MEs that hang *directly* under this level's child regions
+    # (one hop). Deeper nesting is loaded when the user drills into that region.
+    logical_count: dict[tuple[str, str], int] = defaultdict(int)
+    if region_node_ids and child_sbn_id_set:
+        me_uid_to_region: dict[str, str] = {}
+        for ume_ne_id, node_id, parent_node in (
+            db.query(UmeTopoNode.ume_ne_id, UmeTopoNode.node_id, UmeTopoNode.parent_node)
+            .filter(
+                UmeTopoNode.node_type == "TOPO_NODE_ME",
+                UmeTopoNode.parent_node.in_(list(child_sbn_id_set)),
+            )
+            .all()
+        ):
+            uid = str(ume_ne_id or node_id or "").strip()
+            parent = str(parent_node or "").strip()
+            if uid and parent in region_node_ids:
+                me_uid_to_region[uid] = parent
+
+        if me_uid_to_region:
+            fid_to_canvas: dict[str, str] = {}
+            for fid, uid in (
+                db.query(TopoFabricNode.id, TopoFabricNode.ume_ne_id)
+                .filter(TopoFabricNode.ume_ne_id.in_(list(me_uid_to_region.keys())))
+                .all()
+            ):
+                rid = me_uid_to_region.get(str(uid or "").strip(), "")
+                if rid:
+                    fid_to_canvas[str(fid)] = region_node_ids[rid]
+            for fid in direct_me_fids:
+                fid_to_canvas[fid] = fid
+
+            fids = list(fid_to_canvas.keys())
+            if fids:
+                for a_id, b_id in (
+                    db.query(TopoFabricEdge.a_node_id, TopoFabricEdge.b_node_id)
+                    .filter(
+                        TopoFabricEdge.layer == "physical",
+                        TopoFabricEdge.status.in_(status_filter),
+                        TopoFabricEdge.a_node_id.in_(fids),
+                        TopoFabricEdge.b_node_id.in_(fids),
+                    )
+                    .all()
+                ):
+                    a = fid_to_canvas.get(str(a_id))
+                    b = fid_to_canvas.get(str(b_id))
+                    if not a or not b or a == b:
+                        continue
+                    if a in direct_me_fids and b in direct_me_fids:
+                        continue
+                    key = (a, b) if a < b else (b, a)
+                    logical_count[key] += 1
 
     edges_out = physical[:VIEW_GRAPH_EDGE_HARD_CAP]
     truncated = len(physical) > VIEW_GRAPH_EDGE_HARD_CAP
@@ -354,7 +435,6 @@ def get_level_view_graph(
             )
         )
 
-    # Manual nested regions (新建子区域) on this UME canvas.
     from .topology_region_canvas import child_region_nodes_for_view
 
     seen_folder = {str(n.folder_id or "") for n in nodes_out if n.kind == "region"}
@@ -413,18 +493,24 @@ def get_flat_view_graph(
             min_y = float(bbox["min_y"]) - pad_y
             max_y = float(bbox["max_y"]) + pad_y
 
-    extent = (
-        db.query(TopoFabricNode)
+    extent_row = (
+        db.query(
+            func.min(TopoFabricNode.world_x),
+            func.max(TopoFabricNode.world_x),
+            func.min(TopoFabricNode.world_y),
+            func.max(TopoFabricNode.world_y),
+            func.count(TopoFabricNode.id),
+        )
         .filter(TopoFabricNode.world_x.isnot(None), TopoFabricNode.world_y.isnot(None))
-        .all()
+        .one()
     )
-    if not extent:
+    if not int(extent_row[4] or 0):
         return TopologyViewGraphOut(view=_view_out(view), nodes=[], edges=[])
 
-    full_min_x = min(float(n.world_x) for n in extent)
-    full_max_x = max(float(n.world_x) for n in extent)
-    full_min_y = min(float(n.world_y) for n in extent)
-    full_max_y = max(float(n.world_y) for n in extent)
+    full_min_x = float(extent_row[0])
+    full_max_x = float(extent_row[1])
+    full_min_y = float(extent_row[2])
+    full_max_y = float(extent_row[3])
 
     if min_x is None or max_x is None or min_y is None or max_y is None:
         min_x, max_x, min_y, max_y = full_min_x, full_max_x, full_min_y, full_max_y
@@ -441,14 +527,17 @@ def get_flat_view_graph(
         q = q.filter(TopoFabricNode.region_folder_id.in_(list(region_folder_ids)))
     if sbn_id.strip():
         sid = sbn_id.strip()
+        # Attr JSON filter is rare; keep Python filter but only after a bounded fetch.
+        candidates = q.order_by(TopoFabricNode.id.asc()).limit(WORLD_NODE_SOFT_CAP * 5).all()
         nodes = [
             n
-            for n in q.all()
+            for n in candidates
             if str((n.attrs or {}).get("ume_sbn_id") or "") == sid
             or str(n.region_folder_id or "") == sid
         ]
     else:
-        nodes = q.all()
+        # Cap in SQL so we never hydrate 15k ORM rows for a single browser canvas.
+        nodes = q.order_by(TopoFabricNode.id.asc()).limit(WORLD_NODE_SOFT_CAP + 1).all()
 
     truncated = False
     reason = ""
diff --git a/tests/test_topology.py b/tests/test_topology.py
index d57d151..bb6eb79 100644
--- a/tests/test_topology.py
+++ b/tests/test_topology.py
@@ -319,9 +319,17 @@ class FabricTopologyTests(unittest.TestCase):
         self.assertEqual(action, "skipped_self_loop")
 
     def _region(self, name: str = "Test-Region") -> str:
-        return svc.create_folder(
+        """Return the unique L2「根图」canvas id under a new top-level「根」."""
+        top = svc.create_folder(
             self.db, TopologyFolderCreate(name=name, kind="region")
-        ).id
+        )
+        child = (
+            self.db.query(TopoFolder)
+            .filter(TopoFolder.parent_id == top.id, TopoFolder.kind == "region")
+            .order_by(TopoFolder.sort_order.asc(), TopoFolder.created_at.asc())
+            .first()
+        )
+        return child.id if child is not None else top.id
 
     def test_view_crud_and_positions(self) -> None:
         suffix = uuid4().hex[:8]
@@ -394,93 +402,96 @@ class FabricTopologyTests(unittest.TestCase):
         region = svc.create_folder(
             self.db, TopologyFolderCreate(name="East", kind="region")
         )
-        # Creating a region does not auto-create a map — user/MCP adds views.
+        # Top-level「根」is nav-only; unique L2「根图」holds the canvas.
         tree1 = svc.get_topology_tree(self.db)
         assert tree1.root is not None
         east0 = next(c for c in tree1.root.children if c.id == region.id)
         self.assertEqual(east0.views, [])
+        self.assertEqual(len(east0.children), 1)
+        root_map = east0.children[0]
+        self.assertEqual(root_map.name, "根图")
+        self.assertEqual(len(root_map.views), 1)
+        self.assertEqual(root_map.views[0].name, "根图")
 
         view = svc.create_view(
             self.db,
             TopologyViewCreate(
                 name="East-Custom",
-                folder_id=region.id,
+                folder_id=root_map.id,
                 kind="custom",
             ),
         )
-        self.assertEqual(view.folder_id, region.id)
+        self.assertEqual(view.folder_id, root_map.id)
         self.assertEqual(view.kind, "custom")
         self.assertIn("membership", view.filter)
 
         tree2 = svc.get_topology_tree(self.db)
         assert tree2.root is not None
         east = next(c for c in tree2.root.children if c.id == region.id)
-        self.assertTrue(any(v.id == view.id for v in east.views))
-        self.assertEqual(len(east.views), 1)
-        self.assertTrue(all(not getattr(v, "children", None) for v in east.views))
+        rm = east.children[0]
+        self.assertTrue(any(v.id == view.id for v in rm.views))
+        self.assertEqual(len(rm.views), 2)
+        self.assertTrue(all(not getattr(v, "children", None) for v in rm.views))
 
     def test_site_physical_and_custom_flat(self) -> None:
-        region = svc.create_folder(
+        top = svc.create_folder(
             self.db, TopologyFolderCreate(name="Site-R", kind="region")
         )
-        phys = svc.create_view(
-            self.db,
-            TopologyViewCreate(
-                name="Physical",
-                folder_id=region.id,
-                kind="physical",
-            ),
-        )
-        tree = svc.get_topology_tree(self.db)
-        assert tree.root is not None
-        reg = next(c for c in tree.root.children if c.id == region.id)
-        physicals = [v for v in reg.views if v.kind == "physical"]
-        self.assertEqual(len(physicals), 1)
-        self.assertEqual(physicals[0].id, phys.id)
+        tree0 = svc.get_topology_tree(self.db)
+        assert tree0.root is not None
+        nav = next(c for c in tree0.root.children if c.id == top.id)
+        root_map = nav.children[0]
+        self.assertEqual(root_map.name, "根图")
+        auto_phys = root_map.views[0]
+        self.assertEqual(auto_phys.kind, "physical")
 
         custom = svc.create_view(
             self.db,
             TopologyViewCreate(
                 name="Custom-A",
-                folder_id=region.id,
+                folder_id=root_map.id,
                 kind="custom",
             ),
         )
         tree2 = svc.get_topology_tree(self.db)
         assert tree2.root is not None
-        reg2 = next(c for c in tree2.root.children if c.id == region.id)
+        reg2 = next(c for c in tree2.root.children if c.id == top.id).children[0]
         ids = {v.id for v in reg2.views}
-        self.assertIn(phys.id, ids)
+        self.assertIn(auto_phys.id, ids)
         self.assertIn(custom.id, ids)
         # physical first
         self.assertEqual(reg2.views[0].kind, "physical")
 
         with self.assertRaises(Exception):
-            svc.delete_view(self.db, phys.id)
+            svc.delete_view(self.db, auto_phys.id)
         svc.delete_view(self.db, custom.id)
         # force-delete physical does not recreate another map
-        svc.delete_view(self.db, phys.id, force=True)
+        svc.delete_view(self.db, auto_phys.id, force=True)
         tree3 = svc.get_topology_tree(self.db)
         assert tree3.root is not None
-        reg3 = next(c for c in tree3.root.children if c.id == region.id)
+        reg3 = next(c for c in tree3.root.children if c.id == top.id).children[0]
         self.assertEqual(sum(1 for v in reg3.views if v.kind == "physical"), 0)
 
     def test_delete_region_cascades_views(self) -> None:
         region = svc.create_folder(
             self.db, TopologyFolderCreate(name="Del-Region", kind="region")
         )
+        tree0 = svc.get_topology_tree(self.db)
+        assert tree0.root is not None
+        nav = next(c for c in tree0.root.children if c.id == region.id)
+        root_map = nav.children[0]
         custom = svc.create_view(
             self.db,
             TopologyViewCreate(
                 name="Custom-Del",
-                folder_id=region.id,
+                folder_id=root_map.id,
                 kind="custom",
             ),
         )
         tree = svc.get_topology_tree(self.db)
         assert tree.root is not None
         reg = next(c for c in tree.root.children if c.id == region.id)
-        self.assertTrue(any(v.id == custom.id for v in reg.views))
+        self.assertTrue(any(v.id == custom.id for v in reg.children[0].views))
 
         out = svc.delete_folder(self.db, region.id)
         self.assertTrue(out.get("deleted"))
@@ -489,13 +500,20 @@ class FabricTopologyTests(unittest.TestCase):
         self.assertFalse(any(c.id == region.id for c in tree2.root.children))
         self.assertIsNone(self.db.get(TopoView, custom.id))
         self.assertEqual(
-            self.db.query(TopoView).filter(TopoView.folder_id == region.id).count(),
+            self.db.query(TopoView).filter(TopoView.folder_id == root_map.id).count(),
             0,
         )
 
     def test_nested_region_places_icon_on_parent_canvas(self) -> None:
+        # Top-level「根」is nav-only; canvas work happens under unique「根图」.
+        container = svc.create_folder(
+            self.db, TopologyFolderCreate(name="Site-Group", kind="region")
+        )
         parent = svc.create_folder(
-            self.db, TopologyFolderCreate(name="Parent-Canvas", kind="region")
+            self.db,
+            TopologyFolderCreate(
+                name="Parent-Canvas", kind="region", parent_id=container.id
+            ),
         )
         child = svc.create_folder(
             self.db,
@@ -503,7 +521,13 @@ class FabricTopologyTests(unittest.TestCase):
         )
         tree = svc.get_topology_tree(self.db)
         assert tree.root is not None
-        p = next(c for c in tree.root.children if c.id == parent.id)
+        group = next(c for c in tree.root.children if c.id == container.id)
+        self.assertEqual(group.views, [])
+        self.assertEqual(len(group.children), 1)
+        root_map = group.children[0]
+        self.assertEqual(root_map.name, "根图")
+        # Creating under the nav「根」remounts onto「根图」.
+        p = next(c for c in root_map.children if c.id == parent.id)
         self.assertTrue(p.views)
         graph = svc.get_view_graph(self.db, p.views[0].id)
         regions = [n for n in graph.nodes if n.kind == "region"]
@@ -540,6 +564,50 @@ class FabricTopologyTests(unittest.TestCase):
         graph2 = svc.get_view_graph(self.db, p.views[0].id)
         self.assertFalse(any(n.kind == "region" for n in graph2.nodes))
 
+    def test_top_level_stays_nav_when_adding_child(self) -> None:
+        """Creating under「根」remounts onto unique「根图」; top stays nav-only."""
+        top = svc.create_folder(
+            self.db, TopologyFolderCreate(name="East-Nav", kind="region")
+        )
+        child = svc.create_folder(
+            self.db,
+            TopologyFolderCreate(name="Site-A", kind="region", parent_id=top.id),
+        )
+        tree = svc.get_topology_tree(self.db)
+        assert tree.root is not None
+        east = next(c for c in tree.root.children if c.id == top.id)
+        self.assertEqual(east.views, [])
+        self.assertEqual(len(east.children), 1)
+        root_map = east.children[0]
+        self.assertEqual(root_map.name, "根图")
+        self.assertEqual(len(root_map.views), 1)
+        site = next(c for c in root_map.children if c.id == child.id)
+        self.assertEqual(len(site.views), 1)
+        self.assertEqual(site.views[0].name, "Site-A")
+        self.assertNotEqual(site.views[0].name, "Physical topology")
+
+    def test_root_auto_spawns_unique_root_map(self) -> None:
+        top = svc.create_folder(
+            self.db, TopologyFolderCreate(name="West", kind="region")
+        )
+        # Second create under the same「根」must remount under existing「根图」.
+        a = svc.create_folder(
+            self.db,
+            TopologyFolderCreate(name="A", kind="region", parent_id=top.id),
+        )
+        b = svc.create_folder(
+            self.db,
+            TopologyFolderCreate(name="B", kind="region", parent_id=top.id),
+        )
+        tree = svc.get_topology_tree(self.db)
+        assert tree.root is not None
+        west = next(c for c in tree.root.children if c.id == top.id)
+        self.assertEqual(len(west.children), 1)
+        root_map = west.children[0]
+        self.assertEqual(root_map.name, "根图")
+        child_ids = {c.id for c in root_map.children}
+        self.assertEqual(child_ids, {a.id, b.id})
+
     def test_classify_role_region_and_slices(self) -> None:
         from netx_api import topology_classify as clf
         from netx_api.topology_schemas import (
diff --git a/web/src/i18n/en.ts b/web/src/i18n/en.ts
index 0cb646c..454b7eb 100644
--- a/web/src/i18n/en.ts
+++ b/web/src/i18n/en.ts
@@ -1394,7 +1394,11 @@ const en = {
     maps: "Maps",
     tree: "Topology tree",
     treeLoading: "Loading tree…",
-    treeHint: "Regions hold maps you create; open a map to edit the canvas.",
+    graphLoading: "Loading topology…",
+    graphRefreshing: "Refreshing…",
+    canvasEmpty: "No NEs on this map yet",
+    canvasEmptyHint: "Use Add NE, or pick a region that already has devices.",
+    treeHint: "Top level is a Root (nav only); its unique Root Map is the canvas. Open the root map or a sub-region to edit devices.",
     treeSearch: "Search NEs across maps",
     treeSearchPh: "Name / IP",
     treeSearchEmpty: "No matching NEs",
@@ -1402,47 +1406,47 @@ const en = {
     treeSearchNotOnMap: "This NE is not placed on any topology map yet",
     treeSearchViewCount: "{{count}} map(s)",
     treeSearchTruncated: "Showing first 30 of {{total}}",
-    rootName: "Regions",
-    selectRegion: "Select a region",
+    rootName: "Roots",
+    selectRegion: "Select a root or region",
     openMap: "Open map",
-    openRegion: "Open region",
+    openRegion: "Open",
     kindPhysical: "Physical",
     kindCustom: "Custom",
     regionNodeHint: "{{count}}P",
     layerNodeHint: "{{count}} NE(s)",
     layerNodeEmpty: "Click to create & open",
-    rootCanvasHint: "Pick a region from the left tree.",
-    regionCanvasHint: "Open a map to edit devices, or create a custom map.",
-    regionBrowseHint: "Region folder: maps you add. Click to open.",
+    rootCanvasHint: "Pick a root from the left tree.",
+    regionCanvasHint: "Open the root map to edit devices; create sub-regions on that canvas.",
+    regionBrowseHint: "Root folder: unique root map below. Click to open.",
     browserTitle: "Topology folder",
     browserRegionSub: "{{count}} map(s)",
-    browserRegionsSub: "{{count}} region(s)",
-    browserEmptyMaps: "No maps in this region yet.",
+    browserRegionsSub: "{{count}} item(s)",
+    browserEmptyMaps: "No root map under this root yet.",
     addNe: "Add NE",
-    backUp: "Back to region",
-    newRegion: "New region",
-    newRegionName: "New region",
-    newRegionPrompt: "Region name",
+    backUp: "Back",
+    newRegion: "New root",
+    newRegionName: "New root",
+    newRegionPrompt: "Root name",
     newSubRegion: "New sub-region",
     newSubRegionName: "New sub-region",
     newSubRegionPrompt: "Sub-region name",
     subRegionNotOnFlat: "The flat world map has no regions. Create sub-regions on World or a lower-level canvas.",
     worldMapNoDirectNes: "Cannot add NEs on the world map — add them on a sub-region canvas.",
-    subRegionNeedParent: "Open a region canvas first, then create a sub-region.",
-    regionCreated: "Region created",
-    regionDeleted: "Region deleted",
-    deleteRegion: "Delete region",
-    deleteRegionConfirm: "Delete region \"{{name}}\"? Its maps will also be deleted.",
-    renameRegion: "Rename region",
-    renameRegionPrompt: "Region name",
-    regionRenamed: "Region renamed",
-    collapseRegion: "Collapse region",
-    expandRegion: "Expand region",
+    subRegionNeedParent: "Open a root map or region canvas first, then create a sub-region.",
+    regionCreated: "Created",
+    regionDeleted: "Deleted",
+    deleteRegion: "Delete",
+    deleteRegionConfirm: "Delete \"{{name}}\"? Its maps will also be deleted.",
+    renameRegion: "Rename",
+    renameRegionPrompt: "Name",
+    regionRenamed: "Renamed",
+    collapseRegion: "Collapse",
+    expandRegion: "Expand",
     newCustom: "Custom map",
     newCustomName: "Custom topology",
     newCustomPrompt: "Custom map name",
-    folderHint: "Regions group maps. After creating a region, add a physical or custom map yourself.",
-    folderHintShort: "Region folder",
+    folderHint: "Creating a root auto-creates its unique root map. Add sub-regions on that canvas.",
+    folderHintShort: "Root folder",
     outsidePeers: "{{count}} outside peer(s) linked but not on this map",
     projectNeighbors: "Project neighbors",
     projectedNeighbors: "Projected {{count}} neighbor(s) onto the map",
@@ -1467,7 +1471,7 @@ const en = {
     renamed: "Topology map renamed",
     deleteMap: "Delete map",
     deleteMapConfirm: "Delete map \"{{name}}\"? Nodes and edges will be removed.",
-    emptyMaps: "No regions yet. Create a region first.",
+    emptyMaps: "No roots yet. Create a root first.",
     palette: "NE library",
     paletteHint: "Select multiple to add in batch, or drag one onto the canvas",
     paletteDragHint: "Drag onto canvas to add",
diff --git a/web/src/i18n/zh.ts b/web/src/i18n/zh.ts
index 3afd460..2498d2c 100644
--- a/web/src/i18n/zh.ts
+++ b/web/src/i18n/zh.ts
@@ -1385,7 +1385,11 @@ const zh = {
     maps: "拓扑图",
     tree: "拓扑树",
     treeLoading: "加载拓扑树…",
-    treeHint: "区域下为画布列表；点图打开设备画布（区域本身不自动建图）。",
+    graphLoading: "正在加载拓扑图…",
+    graphRefreshing: "刷新中…",
+    canvasEmpty: "这张图上还没有网元",
+    canvasEmptyHint: "可用「添加网元」上图，或从左侧换到有设备的区域。",
+    treeHint: "顶级为「根」（导航）；其下唯一「根图」为画布。点根图或子区域打开设备画布。",
     treeSearch: "全拓扑搜索网元",
     treeSearchPh: "名称 / IP",
     treeSearchEmpty: "没有匹配的网元",
@@ -1393,47 +1397,47 @@ const zh = {
     treeSearchNotOnMap: "该网元尚未出现在任何拓扑图上",
     treeSearchViewCount: "{{count}} 张图",
     treeSearchTruncated: "仅显示前 30 条（共 {{total}}）",
-    rootName: "区域",
-    selectRegion: "请选择区域",
+    rootName: "根",
+    selectRegion: "请选择根或区域",
     openMap: "打开本图",
-    openRegion: "打开区域",
+    openRegion: "打开",
     kindPhysical: "物理拓扑",
     kindCustom: "自定义图",
     regionNodeHint: "{{count}}P",
     layerNodeHint: "{{count}} 个网元",
     layerNodeEmpty: "点击创建并打开",
-    rootCanvasHint: "从左侧选择区域进入目录。",
-    regionCanvasHint: "点击图打开设备画布，或新建自定义图。",
-    regionBrowseHint: "区域目录：自行添加的画布。点击打开。",
+    rootCanvasHint: "从左侧选择根进入目录。",
+    regionCanvasHint: "点击根图打开设备画布；可在根图上新建子区域。",
+    regionBrowseHint: "根目录：下方为唯一根图。点击打开。",
     browserTitle: "拓扑目录",
     browserRegionSub: "共 {{count}} 张拓扑图",
-    browserRegionsSub: "共 {{count}} 个区域",
-    browserEmptyMaps: "此区域还没有拓扑图。",
+    browserRegionsSub: "共 {{count}} 个",
+    browserEmptyMaps: "此根下还没有根图。",
     addNe: "添加网元",
-    backUp: "返回区域",
-    newRegion: "新建区域",
-    newRegionName: "新区域",
-    newRegionPrompt: "区域名称",
+    backUp: "返回",
+    newRegion: "新建根",
+    newRegionName: "新根",
+    newRegionPrompt: "根名称",
     newSubRegion: "新建子区域",
     newSubRegionName: "新子区域",
     newSubRegionPrompt: "子区域名称",
     subRegionNotOnFlat: "完整世界地图不支持子区域，请在 World 或下级区域画布上创建。",
     worldMapNoDirectNes: "世界地图不能直接添加网元，请到某个子区域画布上添加。",
-    subRegionNeedParent: "请先打开一个区域画布，再新建子区域。",
-    regionCreated: "区域已创建",
-    regionDeleted: "区域已删除",
-    deleteRegion: "删除区域",
-    deleteRegionConfirm: "删除区域「{{name}}」？其下画布将一并删除。",
-    renameRegion: "重命名区域",
-    renameRegionPrompt: "区域名称",
-    regionRenamed: "区域已重命名",
-    collapseRegion: "折叠区域",
-    expandRegion: "展开区域",
+    subRegionNeedParent: "请先打开根图或区域画布，再新建子区域。",
+    regionCreated: "已创建",
+    regionDeleted: "已删除",
+    deleteRegion: "删除",
+    deleteRegionConfirm: "删除「{{name}}」？其下画布将一并删除。",
+    renameRegion: "重命名",
+    renameRegionPrompt: "名称",
+    regionRenamed: "已重命名",
+    collapseRegion: "折叠",
+    expandRegion: "展开",
     newCustom: "自定义图",
     newCustomName: "自定义拓扑",
     newCustomPrompt: "自定义拓扑图名称",
-    folderHint: "区域用于分组。新建区域后请自行添加物理拓扑或自定义图。",
-    folderHintShort: "区域目录",
+    folderHint: "新建根时自动创建唯一「根图」。子区域请在根图画布上创建。",
+    folderHintShort: "根目录",
     outsidePeers: "图外对端 {{count}} 个（有链路未上图）",
     projectNeighbors: "投影邻居上图",
     projectedNeighbors: "已投影 {{count}} 个邻居上图",
@@ -1457,7 +1461,7 @@ const zh = {
     renamed: "拓扑图已重命名",
     deleteMap: "删除图",
     deleteMapConfirm: "删除拓扑图「{{name}}」？节点与链路会一并删除。",
-    emptyMaps: "还没有区域，先点「新建区域」。",
+    emptyMaps: "还没有根，先点「新建根」。",
     palette: "网元库",
     paletteHint: "勾选后批量添加；也可拖到画布添加单台",
     paletteDragHint: "拖到画布添加",
diff --git a/web/src/index.css b/web/src/index.css
index 24d84ef..4ed9365 100644
--- a/web/src/index.css
+++ b/web/src/index.css
@@ -1,4 +1,4 @@
-* {
+* {
   box-sizing: border-box;
 }
 
@@ -7003,12 +7003,121 @@ pre {
   color: var(--nm-muted, #5b6b7c);
 }
 
+.topo-canvas__status {
+  gap: 12px;
+  justify-items: center;
+  text-align: center;
+}
+
+.topo-canvas__status p {
+  margin: 0;
+  font-size: 13px;
+}
+
+.topo-loading-spinner {
+  display: inline-block;
+  width: 18px;
+  height: 18px;
+  border: 2px solid rgba(148, 163, 184, 0.28);
+  border-top-color: #60a5fa;
+  border-radius: 50%;
+  animation: topo-spin 0.7s linear infinite;
+}
+
+.topo-loading-spinner--lg {
+  width: 36px;
+  height: 36px;
+  border-width: 3px;
+}
+
+@keyframes topo-spin {
+  to {
+    transform: rotate(360deg);
+  }
+}
+
+.topo-canvas__overlay {
+  position: absolute;
+  inset: 0;
+  z-index: 15;
+  display: grid;
+  place-content: center;
+  justify-items: center;
+  gap: 8px;
+  padding: 24px;
+  text-align: center;
+  pointer-events: none;
+}
+
+.topo-canvas__overlay--loading {
+  background: rgba(11, 18, 32, 0.55);
+  backdrop-filter: blur(2px);
+  pointer-events: auto;
+}
+
+.topo-canvas__overlay--empty {
+  background: transparent;
+  pointer-events: none;
+}
+
+.topo-canvas__overlay-title {
+  margin: 0;
+  font-size: 15px;
+  font-weight: 600;
+  color: #e2e8f0;
+}
+
+.topo-canvas__overlay--empty .topo-canvas__overlay-title {
+  color: #94a3b8;
+}
+
+.topo-canvas__overlay-hint {
+  margin: 0;
+  max-width: 320px;
+  font-size: 12px;
+  line-height: 1.45;
+  color: #94a3b8;
+}
+
+.topo-canvas__refresh {
+  position: absolute;
+  top: 12px;
+  left: 50%;
+  z-index: 21;
+  display: inline-flex;
+  align-items: center;
+  gap: 8px;
+  transform: translateX(-50%);
+  padding: 6px 12px;
+  border-radius: 999px;
+  border: 1px solid rgba(148, 163, 184, 0.28);
+  background: rgba(15, 23, 42, 0.92);
+  color: #cbd5e1;
+  font-size: 12px;
+  box-shadow: 0 8px 20px rgba(0, 0, 0, 0.28);
+  pointer-events: none;
+}
+
+.topo-browser__empty--loading {
+  gap: 12px;
+}
+
+.topo-browser__empty--loading p {
+  margin: 0;
+}
+
 .topo-sidebar .panel__hint {
   margin: 0;
   font-size: 12px;
   color: var(--nm-muted);
 }
 
+.topo-tree-status {
+  display: inline-flex;
+  align-items: center;
+  gap: 8px;
+}
+
 .topo-sidebar .input {
   width: 100%;
   height: 32px;
diff --git a/web/src/pages/TopologyPage.tsx b/web/src/pages/TopologyPage.tsx
index 8060fda..1e24e12 100644
--- a/web/src/pages/TopologyPage.tsx
+++ b/web/src/pages/TopologyPage.tsx
@@ -40,7 +40,6 @@ import {
   createFabricManualEdge,
   createTopologyFolder,
   createTopologyPlaceholder,
-  createTopologyView,
   deleteFabricEdges,
   purgePlaceholderFabricNodes,
   deleteTopologyFolder,
@@ -81,7 +80,6 @@ import type {
   TopologyViewEdgeItem,
   TopologyViewGraph,
   TopologyViewNodeItem,
-  TopologyViewKind,
   TopologyViewRole,
 } from "../types";
 import { alignNodes, layoutGraph, type LayoutKind } from "./topology/layoutGraph";
@@ -182,14 +180,18 @@ function isWorldFlatViewName(name: string | undefined | null): boolean {
 }
 
 /**
- * Region row IS the canvas (SBN / manual region / nested sub-region / World drill).
- * UME World container is nav-only (hex browse for L2 + world map).
+ * Region row IS the canvas for nested / UME SBN / World drill.
+ * Top-level under Network root (and UME World container) are hex-nav only — same as UME World.
  */
 function isRegionCanvasFolder(
   folder: TopologyTreeFolderItem | null | undefined,
+  rootId?: string,
 ): boolean {
   if (!folder) return false;
   if (isUmeWorldContainer(folder)) return false;
+  const rid = String(rootId || "").trim();
+  const parent = String(folder.parent_id || "").trim();
+  if (rid && parent === rid) return false;
   return true;
 }
 
@@ -1183,6 +1185,8 @@ export function TopologyPage() {
   const treeQuery = useQuery({
     queryKey: queryKeys.topologyTree,
     queryFn: fetchTopologyTree,
+    staleTime: liveSync ? 0 : 30_000,
+    refetchOnWindowFocus: liveSync,
     refetchInterval: liveSync ? 5000 : false,
     refetchIntervalInBackground: false,
   });
@@ -1202,6 +1206,8 @@ export function TopologyPage() {
     queryKey: queryKeys.topologyGraph(mapId),
     queryFn: () => fetchTopologyGraph(mapId),
     enabled: Boolean(mapId),
+    staleTime: liveSync ? 0 : 30_000,
+    refetchOnWindowFocus: liveSync,
     refetchInterval: liveSync && mapId ? 3000 : false,
     refetchIntervalInBackground: false,
   });
@@ -1284,6 +1290,8 @@ export function TopologyPage() {
     }
   }, [mapId, selectedFolderId, treeRoot, regions]);
 
+  const rootFolderId = String(treeRoot?.id || "").trim();
+
   const canvasMode = Boolean(mapId);
 
   const activeRegion = useMemo(() => {
@@ -1299,22 +1307,26 @@ export function TopologyPage() {
   const browseEntries = useMemo(
     (): TopologyTreeViewItem[] => {
       // Region === canvas: no map subdirectory listing.
-      // UME World container: hex shows L2 + flat modules (handled separately).
-      if (!activeRegion || isRegionCanvasFolder(activeRegion) || isUmeWorldContainer(activeRegion)) {
+      // UME World / top-level containers: hex shows modules (handled separately).
+      if (
+        !activeRegion ||
+        isRegionCanvasFolder(activeRegion, rootFolderId) ||
+        isUmeWorldContainer(activeRegion)
+      ) {
         return [];
       }
       return activeRegion.views || [];
     },
-    [activeRegion],
+    [activeRegion, rootFolderId],
   );
 
   const hexBrowseRegion = useMemo(() => {
-    // Root hex, or UME World container hex (L2 + world map modules).
+    // Root hex, or nav container hex (UME World / top-level manual).
     if (!activeRegion) return null;
     if (isUmeWorldContainer(activeRegion)) return activeRegion;
-    if (isRegionCanvasFolder(activeRegion)) return null;
+    if (isRegionCanvasFolder(activeRegion, rootFolderId)) return null;
     return activeRegion;
-  }, [activeRegion]);
+  }, [activeRegion, rootFolderId]);
 
   const umeWorldHexModules = useMemo(() => {
     if (!activeRegion || !isUmeWorldContainer(activeRegion)) return null;
@@ -1425,7 +1437,7 @@ export function TopologyPage() {
       expandFolderPath(folderId);
       const folder = findFolderInTree(regions, folderId);
       // Region === canvas: open its primary map (no map subdirectory / hex list).
-      if (isRegionCanvasFolder(folder)) {
+      if (isRegionCanvasFolder(folder, String(treeRoot?.id || ""))) {
         setWorldFocusFolderId("");
         const view = primaryViewOfFolder(folder);
         if (view) {
@@ -1449,6 +1461,7 @@ export function TopologyPage() {
       regions,
       primaryViewOfFolder,
       expandFolderPath,
+      treeRoot?.id,
     ],
   );
 
@@ -1494,16 +1507,22 @@ export function TopologyPage() {
         return;
       }
     }
-    // Leaving other region canvases → root hex.
-    if (isRegionCanvasFolder(folder) || isUmeWorldNavFolder(folder)) {
-      setSelectedFolderId("");
+    // Leaving other region canvases → parent nav container, else root hex.
+    if (isRegionCanvasFolder(folder, String(treeRoot?.id || "")) || isUmeWorldNavFolder(folder)) {
+      const parentId = String(folder?.parent_id || "").trim();
+      const parent = parentId ? findFolderInTree(regions, parentId) : null;
+      if (parent && !isRegionCanvasFolder(parent, String(treeRoot?.id || ""))) {
+        setSelectedFolderId(parent.id);
+      } else {
+        setSelectedFolderId("");
+      }
     }
     setWorldFocusFolderId("");
     setMapId("");
     clearDirty();
     setNodes([]);
     setEdges([]);
-  }, [confirmDiscardIfDirty, clearDirty, setNodes, setEdges, regions, selectedFolderId]);
+  }, [confirmDiscardIfDirty, clearDirty, setNodes, setEdges, regions, selectedFolderId, treeRoot?.id]);
 
   // Deep link from classify search: /topology?view=&ne=
   useEffect(() => {
@@ -1756,10 +1775,9 @@ export function TopologyPage() {
           });
         }
       } else {
+        // Top-level = nav container (UME World pattern): stay on hex browse, do not open canvas.
         setSelectedFolderId(folder.id);
-        const view = hit?.views?.[0];
-        if (view) setMapId(view.id);
-        else setMapId("");
+        setMapId("");
       }
       showOk(t("topology.regionCreated"));
     },
@@ -1787,21 +1805,6 @@ export function TopologyPage() {
     [renameRegionMut, t],
   );
 
-  const createMapMut = useMutation({
-    mutationFn: (input: { folder_id: string; kind: TopologyViewKind; name: string }) =>
-      createTopologyView(input),
-    onSuccess: async (row) => {
-      await queryClient.invalidateQueries({ queryKey: queryKeys.topologyTree });
-      await queryClient.invalidateQueries({ queryKey: queryKeys.topologyMaps });
-      clearDirty();
-      if (row.folder_id) setSelectedFolderId(row.folder_id);
-      setMapId(row.id);
-      showOk(t("topology.newMap"));
-      window.setTimeout(() => promptRenameMap(row.id, row.name), 0);
-    },
-    onError: (err) => showError(String(err)),
-  });
-
   const deleteMapMut = useMutation({
     mutationFn: (id: string) => deleteTopologyMap(id),
     onSuccess: async (_out, id) => {
@@ -1859,19 +1862,6 @@ export function TopologyPage() {
     setCtxMenu(null);
   }, [activeView?.name, selectedFolderId, worldViewId, mapId, regions, createRegionMut, t, showError]);
 
-  const promptNewCustom = useCallback(
-    (folderId: string) => {
-      const name = window.prompt(t("topology.newCustomPrompt"), t("topology.newCustomName"));
-      if (!name?.trim()) return;
-      createMapMut.mutate({
-        folder_id: folderId,
-        kind: "custom",
-        name: name.trim(),
-      });
-    },
-    [createMapMut, t],
-  );
-
   const renderWorldNavFolder = useCallback(
     (folder: TopologyTreeFolderItem, depth: number): ReactNode => {
       const kids = folder.children || [];
@@ -1881,7 +1871,7 @@ export function TopologyPage() {
       const umeNav = isUmeWorldNavFolder(folder);
       // Region === canvas: hide physical/custom view rows; only child regions.
       // UME World container: only「完整世界地图」as a sibling view.
-      const canvasRegion = isRegionCanvasFolder(folder);
+      const canvasRegion = isRegionCanvasFolder(folder, String(treeRoot?.id || ""));
       const visibleViews = canvasRegion
         ? []
         : containerFolder
@@ -2120,6 +2110,7 @@ export function TopologyPage() {
       deleteFolderMut,
       deleteMapMut,
       t,
+      treeRoot?.id,
     ],
   );
 
@@ -3492,6 +3483,15 @@ export function TopologyPage() {
   const outsidePeers = graphQuery.data?.outside_peers || [];
   const graphTruncated = Boolean(graphQuery.data?.truncated);
   const truncateReason = String(graphQuery.data?.truncate_reason || "").trim();
+  const canvasGraphLoading = Boolean(mapId) && (graphQuery.isPending || !graphQuery.data);
+  const canvasGraphEmpty =
+    Boolean(mapId) &&
+    graphQuery.isSuccess &&
+    !graphQuery.isFetching &&
+    (graphQuery.data?.nodes?.length ?? 0) === 0 &&
+    nodes.length === 0;
+  const canvasGraphRefreshing =
+    Boolean(mapId) && liveSync && graphQuery.isFetching && Boolean(graphQuery.data) && !canvasGraphLoading;
   const truncateBannerText = useMemo(() => {
     if (!graphTruncated) return "";
     // World map soft-caps viewport nodes; the banner is noise there.
@@ -3716,7 +3716,16 @@ export function TopologyPage() {
                 ) : null}
               </div>
               {!treeRoot ? (
-                <p className="panel__hint">{treeQuery.isLoading ? t("topology.treeLoading") : t("topology.emptyMaps")}</p>
+                <p className="panel__hint topo-tree-status" role="status">
+                  {treeQuery.isLoading ? (
+                    <>
+                      <span className="topo-loading-spinner" aria-hidden="true" />
+                      {t("topology.treeLoading")}
+                    </>
+                  ) : (
+                    t("topology.emptyMaps")
+                  )}
+                </p>
               ) : regions.length === 0 ? (
                 <p className="panel__hint">{t("topology.emptyMaps")}</p>
               ) : (
@@ -3760,7 +3769,7 @@ export function TopologyPage() {
                   <>
                     <span className="topo-breadcrumb__sep">/</span>
                     {activeView &&
-                    isRegionCanvasFolder(activeRegion) &&
+                    isRegionCanvasFolder(activeRegion, rootFolderId) &&
                     primaryViewOfFolder(activeRegion)?.id === activeView.id ? (
                       <span className="topo-breadcrumb__current">
                         {regionDisplayName(activeRegion)}
@@ -3780,7 +3789,7 @@ export function TopologyPage() {
                 {activeView &&
                 !(
                   activeRegion &&
-                  isRegionCanvasFolder(activeRegion) &&
+                  isRegionCanvasFolder(activeRegion, rootFolderId) &&
                   primaryViewOfFolder(activeRegion)?.id === activeView.id
                 ) ? (
                   <>
@@ -4069,7 +4078,12 @@ export function TopologyPage() {
               </button>
             </div>
             {!hexBrowseRegion ? (
-              regions.length === 0 ? (
+              treeQuery.isLoading ? (
+                <div className="topo-browser__empty topo-browser__empty--loading" role="status">
+                  <span className="topo-loading-spinner" aria-hidden="true" />
+                  <p>{t("topology.treeLoading")}</p>
+                </div>
+              ) : regions.length === 0 ? (
                 <div className="topo-browser__empty">
                   <span className="topo-browser__empty-icon" aria-hidden="true">
                     <RegionGlyph size={36} />
@@ -4207,22 +4221,36 @@ export function TopologyPage() {
                   </button>
                 ) : null}
               </div>
-            ) : browseEntries.length === 0 ? (
-              <div className="topo-browser__grid topo-browser__grid--regions">
-                <button
-                  type="button"
-                  className="topo-region-hex topo-region-hex--add"
-                  onClick={() => promptNewCustom(hexBrowseRegion.id)}
-                  title={t("topology.newCustom")}
-                >
-                  <span className="topo-region-hex__plus" aria-hidden="true">
-                    +
-                  </span>
-                  <span className="topo-region-hex__name">{t("topology.newCustom")}</span>
-                </button>
-              </div>
             ) : (
               <div className="topo-browser__grid topo-browser__grid--regions">
+                {(hexBrowseRegion.children || []).map((region, idx) => (
+                  <button
+                    key={region.id}
+                    type="button"
+                    className={`topo-region-hex topo-region-hex--tone-${idx % 5}${
+                      selectedFolderId === region.id ? " is-selected" : ""
+                    }${hotBrowseKey === `region:${region.id}` ? " is-hot" : ""}`}
+                    onMouseEnter={() => setHotBrowseKey(`region:${region.id}`)}
+                    onMouseLeave={() =>
+                      setHotBrowseKey((k) => (k === `region:${region.id}` ? "" : k))
+                    }
+                    onClick={() => goRegion(region.id)}
+                    title={t("topology.openRegion")}
+                  >
+                    <span className="topo-region-hex__icon" aria-hidden="true">
+                      <RegionGlyph size={22} />
+                    </span>
+                    <span className="topo-region-hex__title">
+                      <span className="topo-region-hex__name">{regionDisplayName(region)}</span>
+                      <span className="topo-region-hex__meta">
+                        {t("topology.regionNodeHint").replace(
+                          "{{count}}",
+                          String(region.views?.length || region.children?.length || 0),
+                        )}
+                      </span>
+                    </span>
+                  </button>
+                ))}
                 {browseEntries.map((v, idx) => {
                   const isPhysical = String(v.kind) === "physical";
                   const tone = isPhysical ? "physical" : String((idx + 1) % 5);
@@ -4237,7 +4265,7 @@ export function TopologyPage() {
                       onMouseLeave={() =>
                         setHotBrowseKey((k) => (k === `view:${v.id}` ? "" : k))
                       }
-                      onClick={() => goCanvas(v.id, activeRegion.id)}
+                      onClick={() => goCanvas(v.id, hexBrowseRegion.id)}
                       title={t("topology.openMap")}
                     >
                       <span className="topo-region-hex__icon" aria-hidden="true">
@@ -4250,17 +4278,23 @@ export function TopologyPage() {
                     </button>
                   );
                 })}
-                <button
-                  type="button"
-                  className="topo-region-hex topo-region-hex--add"
-                  onClick={() => promptNewCustom(hexBrowseRegion.id)}
-                  title={t("topology.newCustom")}
-                >
-                  <span className="topo-region-hex__plus" aria-hidden="true">
-                    +
-                  </span>
-                  <span className="topo-region-hex__name">{t("topology.newCustom")}</span>
-                </button>
+                {/* Top-level「根」is nav-only with unique「根图」— no extra L2 / custom map. */}
+                {String(hexBrowseRegion.parent_id || "") !== rootFolderId ? (
+                  <button
+                    type="button"
+                    className="topo-region-hex topo-region-hex--add"
+                    onClick={() => {
+                      setSelectedFolderId(hexBrowseRegion.id);
+                      promptNewSubRegion();
+                    }}
+                    title={t("topology.newSubRegion")}
+                  >
+                    <span className="topo-region-hex__plus" aria-hidden="true">
+                      +
+                    </span>
+                    <span className="topo-region-hex__name">{t("topology.newSubRegion")}</span>
+                  </button>
+                ) : null}
               </div>
             )}
           </div>
@@ -4905,8 +4939,29 @@ export function TopologyPage() {
                 </ReactFlow>
               </TopoDisplayContext.Provider>
             ) : (
-              <div className="topo-canvas__empty">{t("topology.treeLoading")}</div>
+              <div className="topo-canvas__empty topo-canvas__status" role="status">
+                <span className="topo-loading-spinner" aria-hidden="true" />
+                <p>{t("topology.treeLoading")}</p>
+              </div>
             )}
+            {treeRoot && canvasGraphLoading ? (
+              <div className="topo-canvas__overlay topo-canvas__overlay--loading" role="status">
+                <span className="topo-loading-spinner topo-loading-spinner--lg" aria-hidden="true" />
+                <p className="topo-canvas__overlay-title">{t("topology.graphLoading")}</p>
+              </div>
+            ) : null}
+            {treeRoot && canvasGraphEmpty ? (
+              <div className="topo-canvas__overlay topo-canvas__overlay--empty" role="status">
+                <p className="topo-canvas__overlay-title">{t("topology.canvasEmpty")}</p>
+                <p className="topo-canvas__overlay-hint">{t("topology.canvasEmptyHint")}</p>
+              </div>
+            ) : null}
+            {treeRoot && canvasGraphRefreshing ? (
+              <div className="topo-canvas__refresh" role="status" aria-live="polite">
+                <span className="topo-loading-spinner" aria-hidden="true" />
+                {t("topology.graphRefreshing")}
+              </div>
+            ) : null}
           </div>
         )}
       </main>